Merge pull request #1405 from fjl/lean-trie

core, trie: new trie

30 files changed, 1515 insertions, 1059 deletions

diff --git a/build/update-license.go b/build/update-license.go
index e28005cbd..04f52a13c 100644
--- a/build/update-license.go
+++ b/build/update-license.go
@@ -46,9 +46,10 @@ var (
 	skipPrefixes = []string{
 		// boring stuff
 		"Godeps/", "tests/files/", "build/",
-		// don't relicense vendored packages
+		// don't relicense vendored sources
 		"crypto/sha3/", "crypto/ecies/", "logger/glog/",
 		"crypto/curve.go",
+		"trie/arc.go",
 	}
 
 	// paths with this prefix are licensed as GPL. all other files are LGPL.
diff --git a/core/block_processor.go b/core/block_processor.go
index 238b2db95..40590bdc5 100644
--- a/core/block_processor.go
+++ b/core/block_processor.go
@@ -100,10 +100,8 @@ func (self *BlockProcessor) ApplyTransaction(gp GasPool, statedb *state.StateDB,
 	}
 
 	// Update the state with pending changes
-	statedb.SyncIntermediate()
-
 	usedGas.Add(usedGas, gas)
-	receipt := types.NewReceipt(statedb.Root().Bytes(), usedGas)
+	receipt := types.NewReceipt(statedb.IntermediateRoot().Bytes(), usedGas)
 	receipt.TxHash = tx.Hash()
 	receipt.GasUsed = new(big.Int).Set(gas)
 	if MessageCreatesContract(tx) {
@@ -265,16 +263,16 @@ func (sm *BlockProcessor) processWithParent(block, parent *types.Block) (logs st
 	// Accumulate static rewards; block reward, uncle's and uncle inclusion.
 	AccumulateRewards(state, header, uncles)
 
-	// Commit state objects/accounts to a temporary trie (does not save)
-	// used to calculate the state root.
-	state.SyncObjects()
-	if header.Root != state.Root() {
-		err = fmt.Errorf("invalid merkle root. received=%x got=%x", header.Root, state.Root())
-		return
+	// Commit state objects/accounts to a database batch and calculate
+	// the state root. The database is not modified if the root
+	// doesn't match.
+	root, batch := state.CommitBatch()
+	if header.Root != root {
+		return nil, nil, fmt.Errorf("invalid merkle root: header=%x computed=%x", header.Root, root)
 	}
 
-	// Sync the current block's state to the database
-	state.Sync()
+	// Execute the database writes.
+	batch.Write()
 
 	return state.Logs(), receipts, nil
 }
diff --git a/core/chain_makers.go b/core/chain_makers.go
index 70233438d..3af9b0b89 100644
--- a/core/chain_makers.go
+++ b/core/chain_makers.go
@@ -17,6 +17,7 @@
 package core
 
 import (
+	"fmt"
 	"math/big"
 
 	"github.com/ethereum/go-ethereum/common"
@@ -94,9 +95,9 @@ func (b *BlockGen) AddTx(tx *types.Transaction) {
 	if err != nil {
 		panic(err)
 	}
-	b.statedb.SyncIntermediate()
+	root := b.statedb.IntermediateRoot()
 	b.header.GasUsed.Add(b.header.GasUsed, gas)
-	receipt := types.NewReceipt(b.statedb.Root().Bytes(), b.header.GasUsed)
+	receipt := types.NewReceipt(root.Bytes(), b.header.GasUsed)
 	logs := b.statedb.GetLogs(tx.Hash())
 	receipt.SetLogs(logs)
 	receipt.Bloom = types.CreateBloom(types.Receipts{receipt})
@@ -163,8 +164,11 @@ func GenerateChain(parent *types.Block, db ethdb.Database, n int, gen func(int,
 			gen(i, b)
 		}
 		AccumulateRewards(statedb, h, b.uncles)
-		statedb.SyncIntermediate()
-		h.Root = statedb.Root()
+		root, err := statedb.Commit()
+		if err != nil {
+			panic(fmt.Sprintf("state write error: %v", err))
+		}
+		h.Root = root
 		return types.NewBlock(h, b.txs, b.uncles, b.receipts)
 	}
 	for i := 0; i < n; i++ {
@@ -184,7 +188,7 @@ func makeHeader(parent *types.Block, state *state.StateDB) *types.Header {
 		time = new(big.Int).Add(parent.Time(), big.NewInt(10)) // block time is fixed at 10 seconds
 	}
 	return &types.Header{
-		Root:       state.Root(),
+		Root:       state.IntermediateRoot(),
 		ParentHash: parent.Hash(),
 		Coinbase:   parent.Coinbase(),
 		Difficulty: CalcDifficulty(time.Uint64(), new(big.Int).Sub(time, big.NewInt(10)).Uint64(), parent.Number(), parent.Difficulty()),
diff --git a/core/chain_manager.go b/core/chain_manager.go
index 383fce70c..55ef3fcad 100644
--- a/core/chain_manager.go
+++ b/core/chain_manager.go
@@ -840,8 +840,8 @@ out:
 }
 
 func blockErr(block *types.Block, err error) {
-	h := block.Header()
-	glog.V(logger.Error).Infof("Bad block #%v (%x)\n", h.Number, h.Hash().Bytes())
-	glog.V(logger.Error).Infoln(err)
-	glog.V(logger.Debug).Infoln(verifyNonces)
+	if glog.V(logger.Error) {
+		glog.Errorf("Bad block #%v (%s)\n", block.Number(), block.Hash().Hex())
+		glog.Errorf("    %v", err)
+	}
 }
diff --git a/core/genesis.go b/core/genesis.go
index b2346da65..bf97da2e2 100644
--- a/core/genesis.go
+++ b/core/genesis.go
@@ -69,7 +69,7 @@ func WriteGenesisBlock(chainDb ethdb.Database, reader io.Reader) (*types.Block,
 			statedb.SetState(address, common.HexToHash(key), common.HexToHash(value))
 		}
 	}
-	statedb.SyncObjects()
+	root, stateBatch := statedb.CommitBatch()
 
 	difficulty := common.String2Big(genesis.Difficulty)
 	block := types.NewBlock(&types.Header{
@@ -81,7 +81,7 @@ func WriteGenesisBlock(chainDb ethdb.Database, reader io.Reader) (*types.Block,
 		Difficulty: difficulty,
 		MixDigest:  common.HexToHash(genesis.Mixhash),
 		Coinbase:   common.HexToAddress(genesis.Coinbase),
-		Root:       statedb.Root(),
+		Root:       root,
 	}, nil, nil, nil)
 
 	if block := GetBlock(chainDb, block.Hash()); block != nil {
@@ -92,8 +92,10 @@ func WriteGenesisBlock(chainDb ethdb.Database, reader io.Reader) (*types.Block,
 		}
 		return block, nil
 	}
-	statedb.Sync()
 
+	if err := stateBatch.Write(); err != nil {
+		return nil, fmt.Errorf("cannot write state: %v", err)
+	}
 	if err := WriteTd(chainDb, block.Hash(), difficulty); err != nil {
 		return nil, err
 	}
@@ -115,12 +117,14 @@ func GenesisBlockForTesting(db ethdb.Database, addr common.Address, balance *big
 	statedb := state.New(common.Hash{}, db)
 	obj := statedb.GetOrNewStateObject(addr)
 	obj.SetBalance(balance)
-	statedb.SyncObjects()
-	statedb.Sync()
+	root, err := statedb.Commit()
+	if err != nil {
+		panic(fmt.Sprintf("cannot write state: %v", err))
+	}
 	block := types.NewBlock(&types.Header{
 		Difficulty: params.GenesisDifficulty,
 		GasLimit:   params.GenesisGasLimit,
-		Root:       statedb.Root(),
+		Root:       root,
 	}, nil, nil, nil)
 	return block
 }
diff --git a/core/state/state_object.go b/core/state/state_object.go
index 353f2357b..40af9ed9c 100644
--- a/core/state/state_object.go
+++ b/core/state/state_object.go
@@ -90,15 +90,13 @@ type StateObject struct {
 
 func NewStateObject(address common.Address, db ethdb.Database) *StateObject {
 	object := &StateObject{db: db, address: address, balance: new(big.Int), gasPool: new(big.Int), dirty: true}
-	object.trie = trie.NewSecure((common.Hash{}).Bytes(), db)
+	object.trie, _ = trie.NewSecure(common.Hash{}, db)
 	object.storage = make(Storage)
 	object.gasPool = new(big.Int)
-
 	return object
 }
 
 func NewStateObjectFromBytes(address common.Address, data []byte, db ethdb.Database) *StateObject {
-	// TODO clean me up
 	var extobject struct {
 		Nonce    uint64
 		Balance  *big.Int
@@ -107,7 +105,13 @@ func NewStateObjectFromBytes(address common.Address, data []byte, db ethdb.Datab
 	}
 	err := rlp.Decode(bytes.NewReader(data), &extobject)
 	if err != nil {
-		fmt.Println(err)
+		glog.Errorf("can't decode state object %x: %v", address, err)
+		return nil
+	}
+	trie, err := trie.NewSecure(extobject.Root, db)
+	if err != nil {
+		// TODO: bubble this up or panic
+		glog.Errorf("can't create account trie with root %x: %v", extobject.Root[:], err)
 		return nil
 	}
 
@@ -115,11 +119,10 @@ func NewStateObjectFromBytes(address common.Address, data []byte, db ethdb.Datab
 	object.nonce = extobject.Nonce
 	object.balance = extobject.Balance
 	object.codeHash = extobject.CodeHash
-	object.trie = trie.NewSecure(extobject.Root[:], db)
+	object.trie = trie
 	object.storage = make(map[string]common.Hash)
 	object.gasPool = new(big.Int)
 	object.code, _ = db.Get(extobject.CodeHash)
-
 	return object
 }
 
@@ -215,6 +218,7 @@ func (c *StateObject) ReturnGas(gas, price *big.Int) {}
 
 func (self *StateObject) SetGasLimit(gasLimit *big.Int) {
 	self.gasPool = new(big.Int).Set(gasLimit)
+	self.dirty = true
 
 	if glog.V(logger.Core) {
 		glog.Infof("%x: gas (+ %v)", self.Address(), self.gasPool)
@@ -225,19 +229,14 @@ func (self *StateObject) SubGas(gas, price *big.Int) error {
 	if self.gasPool.Cmp(gas) < 0 {
 		return GasLimitError(self.gasPool, gas)
 	}
-
 	self.gasPool.Sub(self.gasPool, gas)
-
-	rGas := new(big.Int).Set(gas)
-	rGas.Mul(rGas, price)
-
 	self.dirty = true
-
 	return nil
 }
 
 func (self *StateObject) AddGas(gas, price *big.Int) {
 	self.gasPool.Add(self.gasPool, gas)
+	self.dirty = true
 }
 
 func (self *StateObject) Copy() *StateObject {
diff --git a/core/state/state_test.go b/core/state/state_test.go
index 60836738e..b5a7f4081 100644
--- a/core/state/state_test.go
+++ b/core/state/state_test.go
@@ -89,8 +89,7 @@ func TestNull(t *testing.T) {
 	//value := common.FromHex("0x823140710bf13990e4500136726d8b55")
 	var value common.Hash
 	state.SetState(address, common.Hash{}, value)
-	state.SyncIntermediate()
-	state.Sync()
+	state.Commit()
 	value = state.GetState(address, common.Hash{})
 	if !common.EmptyHash(value) {
 		t.Errorf("expected empty hash. got %x", value)
diff --git a/core/state/statedb.go b/core/state/statedb.go
index 24f97e32a..4233c763b 100644
--- a/core/state/statedb.go
+++ b/core/state/statedb.go
@@ -35,7 +35,6 @@ import (
 type StateDB struct {
 	db   ethdb.Database
 	trie *trie.SecureTrie
-	root common.Hash
 
 	stateObjects map[string]*StateObject
 
@@ -49,12 +48,19 @@ type StateDB struct {
 
 // Create a new state from a given trie
 func New(root common.Hash, db ethdb.Database) *StateDB {
-	trie := trie.NewSecure(root[:], db)
-	return &StateDB{root: root, db: db, trie: trie, stateObjects: make(map[string]*StateObject), refund: new(big.Int), logs: make(map[common.Hash]Logs)}
-}
-
-func (self *StateDB) PrintRoot() {
-	self.trie.Trie.PrintRoot()
+	tr, err := trie.NewSecure(root, db)
+	if err != nil {
+		// TODO: bubble this up
+		tr, _ = trie.NewSecure(common.Hash{}, db)
+		glog.Errorf("can't create state trie with root %x: %v", root[:], err)
+	}
+	return &StateDB{
+		db:           db,
+		trie:         tr,
+		stateObjects: make(map[string]*StateObject),
+		refund:       new(big.Int),
+		logs:         make(map[common.Hash]Logs),
+	}
 }
 
 func (self *StateDB) StartRecord(thash, bhash common.Hash, ti int) {
@@ -196,7 +202,6 @@ func (self *StateDB) UpdateStateObject(stateObject *StateObject) {
 	if len(stateObject.CodeHash()) > 0 {
 		self.db.Put(stateObject.CodeHash(), stateObject.code)
 	}
-
 	addr := stateObject.Address()
 	self.trie.Update(addr[:], stateObject.RlpEncode())
 }
@@ -207,6 +212,7 @@ func (self *StateDB) DeleteStateObject(stateObject *StateObject) {
 
 	addr := stateObject.Address()
 	self.trie.Delete(addr[:])
+	//delete(self.stateObjects, addr.Str())
 }
 
 // Retrieve a state object given my the address. Nil if not found
@@ -303,65 +309,67 @@ func (self *StateDB) Set(state *StateDB) {
 	self.logSize = state.logSize
 }
 
-func (s *StateDB) Root() common.Hash {
-	return common.BytesToHash(s.trie.Root())
-}
-
-// Syncs the trie and all siblings
-func (s *StateDB) Sync() {
-	// Sync all nested states
+// IntermediateRoot computes the current root hash of the state trie.
+// It is called in between transactions to get the root hash that
+// goes into transaction receipts.
+func (s *StateDB) IntermediateRoot() common.Hash {
+	s.refund = new(big.Int)
 	for _, stateObject := range s.stateObjects {
-		stateObject.trie.Commit()
-	}
-
-	s.trie.Commit()
-
-	s.Empty()
-}
-
-func (self *StateDB) Empty() {
-	self.stateObjects = make(map[string]*StateObject)
-	self.refund = new(big.Int)
-}
-
-func (self *StateDB) Refunds() *big.Int {
-	return self.refund
-}
-
-// SyncIntermediate updates the intermediate state and all mid steps
-func (self *StateDB) SyncIntermediate() {
-	self.refund = new(big.Int)
-
-	for _, stateObject := range self.stateObjects {
 		if stateObject.dirty {
 			if stateObject.remove {
-				self.DeleteStateObject(stateObject)
+				s.DeleteStateObject(stateObject)
 			} else {
 				stateObject.Update()
-
-				self.UpdateStateObject(stateObject)
+				s.UpdateStateObject(stateObject)
 			}
 			stateObject.dirty = false
 		}
 	}
+	return s.trie.Hash()
 }
 
-// SyncObjects syncs the changed objects to the trie
-func (self *StateDB) SyncObjects() {
-	self.trie = trie.NewSecure(self.root[:], self.db)
+// Commit commits all state changes to the database.
+func (s *StateDB) Commit() (root common.Hash, err error) {
+	return s.commit(s.db)
+}
 
-	self.refund = new(big.Int)
+// CommitBatch commits all state changes to a write batch but does not
+// execute the batch. It is used to validate state changes against
+// the root hash stored in a block.
+func (s *StateDB) CommitBatch() (root common.Hash, batch ethdb.Batch) {
+	batch = s.db.NewBatch()
+	root, _ = s.commit(batch)
+	return root, batch
+}
 
-	for _, stateObject := range self.stateObjects {
+func (s *StateDB) commit(db trie.DatabaseWriter) (common.Hash, error) {
+	s.refund = new(big.Int)
+
+	for _, stateObject := range s.stateObjects {
 		if stateObject.remove {
-			self.DeleteStateObject(stateObject)
+			// If the object has been removed, don't bother syncing it
+			// and just mark it for deletion in the trie.
+			s.DeleteStateObject(stateObject)
 		} else {
+			// Write any storage changes in the state object to its trie.
 			stateObject.Update()
-
-			self.UpdateStateObject(stateObject)
+			// Commit the trie of the object to the batch.
+			// This updates the trie root internally, so
+			// getting the root hash of the storage trie
+			// through UpdateStateObject is fast.
+			if _, err := stateObject.trie.CommitTo(db); err != nil {
+				return common.Hash{}, err
+			}
+			// Update the object in the account trie.
+			s.UpdateStateObject(stateObject)
 		}
 		stateObject.dirty = false
 	}
+	return s.trie.CommitTo(db)
+}
+
+func (self *StateDB) Refunds() *big.Int {
+	return self.refund
 }
 
 // Debug stuff
diff --git a/core/types/derive_sha.go b/core/types/derive_sha.go
index 478edb0e8..00c42c5bc 100644
--- a/core/types/derive_sha.go
+++ b/core/types/derive_sha.go
@@ -17,8 +17,9 @@
 package types
 
 import (
+	"bytes"
+
 	"github.com/ethereum/go-ethereum/common"
-	"github.com/ethereum/go-ethereum/ethdb"
 	"github.com/ethereum/go-ethereum/rlp"
 	"github.com/ethereum/go-ethereum/trie"
 )
@@ -29,12 +30,12 @@ type DerivableList interface {
 }
 
 func DeriveSha(list DerivableList) common.Hash {
-	db, _ := ethdb.NewMemDatabase()
-	trie := trie.New(nil, db)
+	keybuf := new(bytes.Buffer)
+	trie := new(trie.Trie)
 	for i := 0; i < list.Len(); i++ {
-		key, _ := rlp.EncodeToBytes(uint(i))
-		trie.Update(key, list.GetRlp(i))
+		keybuf.Reset()
+		rlp.Encode(keybuf, uint(i))
+		trie.Update(keybuf.Bytes(), list.GetRlp(i))
 	}
-
-	return common.BytesToHash(trie.Root())
+	return trie.Hash()
 }
diff --git a/miner/worker.go b/miner/worker.go
index 22d0b9b6e..098f42a72 100644
--- a/miner/worker.go
+++ b/miner/worker.go
@@ -266,7 +266,6 @@ func (self *worker) wait() {
 			block := result.Block
 			work := result.Work
 
-			work.state.Sync()
 			if self.fullValidation {
 				if _, err := self.chain.InsertChain(types.Blocks{block}); err != nil {
 					glog.V(logger.Error).Infoln("mining err", err)
@@ -274,6 +273,7 @@ func (self *worker) wait() {
 				}
 				go self.mux.Post(core.NewMinedBlockEvent{block})
 			} else {
+				work.state.Commit()
 				parent := self.chain.GetBlock(block.ParentHash())
 				if parent == nil {
 					glog.V(logger.Error).Infoln("Invalid block found during mining")
@@ -528,8 +528,7 @@ func (self *worker) commitNewWork() {
 	if atomic.LoadInt32(&self.mining) == 1 {
 		// commit state root after all state transitions.
 		core.AccumulateRewards(work.state, header, uncles)
-		work.state.SyncObjects()
-		header.Root = work.state.Root()
+		header.Root = work.state.IntermediateRoot()
 	}
 
 	// create the new block whose nonce will be mined.
diff --git a/tests/block_test_util.go b/tests/block_test_util.go
index 3ca00bae8..33577cf55 100644
--- a/tests/block_test_util.go
+++ b/tests/block_test_util.go
@@ -253,13 +253,13 @@ func (t *BlockTest) InsertPreState(ethereum *eth.Ethereum) (*state.StateDB, erro
 			statedb.SetState(common.HexToAddress(addrString), common.HexToHash(k), common.HexToHash(v))
 		}
 	}
-	// sync objects to trie
-	statedb.SyncObjects()
-	// sync trie to disk
-	statedb.Sync()
 
-	if !bytes.Equal(t.Genesis.Root().Bytes(), statedb.Root().Bytes()) {
-		return nil, fmt.Errorf("computed state root does not match genesis block %x %x", t.Genesis.Root().Bytes()[:4], statedb.Root().Bytes()[:4])
+	root, err := statedb.Commit()
+	if err != nil {
+		return nil, fmt.Errorf("error writing state: %v", err)
+	}
+	if t.Genesis.Root() != root {
+		return nil, fmt.Errorf("computed state root does not match genesis block: genesis=%x computed=%x", t.Genesis.Root().Bytes()[:4], root.Bytes()[:4])
 	}
 	return statedb, nil
 }
diff --git a/tests/state_test_util.go b/tests/state_test_util.go
index 95ecdd0a8..3d8dfca31 100644
--- a/tests/state_test_util.go
+++ b/tests/state_test_util.go
@@ -201,9 +201,9 @@ func runStateTest(test VmTest) error {
 		}
 	}
 
-	statedb.Sync()
-	if common.HexToHash(test.PostStateRoot) != statedb.Root() {
-		return fmt.Errorf("Post state root error. Expected %s, got %x", test.PostStateRoot, statedb.Root())
+	root, _ := statedb.Commit()
+	if common.HexToHash(test.PostStateRoot) != root {
+		return fmt.Errorf("Post state root error. Expected %s, got %x", test.PostStateRoot, root)
 	}
 
 	// check logs
@@ -247,7 +247,7 @@ func RunState(statedb *state.StateDB, env, tx map[string]string) ([]byte, state.
 	if core.IsNonceErr(err) || core.IsInvalidTxErr(err) || state.IsGasLimitErr(err) {
 		statedb.Set(snapshot)
 	}
-	statedb.SyncObjects()
+	statedb.Commit()
 
 	return ret, vmenv.state.Logs(), vmenv.Gas, err
 }
diff --git a/trie/arc.go b/trie/arc.go
new file mode 100644
index 000000000..9da012e16
--- /dev/null
+++ b/trie/arc.go
@@ -0,0 +1,194 @@
+// Copyright (c) 2015 Hans Alexander Gugel <alexander.gugel@gmail.com>
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// This file contains a modified version of package arc from
+// https://github.com/alexanderGugel/arc
+//
+// It implements the ARC (Adaptive Replacement Cache) algorithm as detailed in
+// https://www.usenix.org/legacy/event/fast03/tech/full_papers/megiddo/megiddo.pdf
+
+package trie
+
+import (
+	"container/list"
+	"sync"
+)
+
+type arc struct {
+	p     int
+	c     int
+	t1    *list.List
+	b1    *list.List
+	t2    *list.List
+	b2    *list.List
+	cache map[string]*entry
+	mutex sync.Mutex
+}
+
+type entry struct {
+	key   hashNode
+	value node
+	ll    *list.List
+	el    *list.Element
+}
+
+// newARC returns a new Adaptive Replacement Cache with the
+// given capacity.
+func newARC(c int) *arc {
+	return &arc{
+		c:     c,
+		t1:    list.New(),
+		b1:    list.New(),
+		t2:    list.New(),
+		b2:    list.New(),
+		cache: make(map[string]*entry, c),
+	}
+}
+
+// Put inserts a new key-value pair into the cache.
+// This optimizes future access to this entry (side effect).
+func (a *arc) Put(key hashNode, value node) bool {
+	a.mutex.Lock()
+	defer a.mutex.Unlock()
+	ent, ok := a.cache[string(key)]
+	if ok != true {
+		ent = &entry{key: key, value: value}
+		a.req(ent)
+		a.cache[string(key)] = ent
+	} else {
+		ent.value = value
+		a.req(ent)
+	}
+	return ok
+}
+
+// Get retrieves a previously via Set inserted entry.
+// This optimizes future access to this entry (side effect).
+func (a *arc) Get(key hashNode) (value node, ok bool) {
+	a.mutex.Lock()
+	defer a.mutex.Unlock()
+	ent, ok := a.cache[string(key)]
+	if ok {
+		a.req(ent)
+		return ent.value, ent.value != nil
+	}
+	return nil, false
+}
+
+func (a *arc) req(ent *entry) {
+	if ent.ll == a.t1 || ent.ll == a.t2 {
+		// Case I
+		ent.setMRU(a.t2)
+	} else if ent.ll == a.b1 {
+		// Case II
+		// Cache Miss in t1 and t2
+
+		// Adaptation
+		var d int
+		if a.b1.Len() >= a.b2.Len() {
+			d = 1
+		} else {
+			d = a.b2.Len() / a.b1.Len()
+		}
+		a.p = a.p + d
+		if a.p > a.c {
+			a.p = a.c
+		}
+
+		a.replace(ent)
+		ent.setMRU(a.t2)
+	} else if ent.ll == a.b2 {
+		// Case III
+		// Cache Miss in t1 and t2
+
+		// Adaptation
+		var d int
+		if a.b2.Len() >= a.b1.Len() {
+			d = 1
+		} else {
+			d = a.b1.Len() / a.b2.Len()
+		}
+		a.p = a.p - d
+		if a.p < 0 {
+			a.p = 0
+		}
+
+		a.replace(ent)
+		ent.setMRU(a.t2)
+	} else if ent.ll == nil {
+		// Case IV
+
+		if a.t1.Len()+a.b1.Len() == a.c {
+			// Case A
+			if a.t1.Len() < a.c {
+				a.delLRU(a.b1)
+				a.replace(ent)
+			} else {
+				a.delLRU(a.t1)
+			}
+		} else if a.t1.Len()+a.b1.Len() < a.c {
+			// Case B
+			if a.t1.Len()+a.t2.Len()+a.b1.Len()+a.b2.Len() >= a.c {
+				if a.t1.Len()+a.t2.Len()+a.b1.Len()+a.b2.Len() == 2*a.c {
+					a.delLRU(a.b2)
+				}
+				a.replace(ent)
+			}
+		}
+
+		ent.setMRU(a.t1)
+	}
+}
+
+func (a *arc) delLRU(list *list.List) {
+	lru := list.Back()
+	list.Remove(lru)
+	delete(a.cache, string(lru.Value.(*entry).key))
+}
+
+func (a *arc) replace(ent *entry) {
+	if a.t1.Len() > 0 && ((a.t1.Len() > a.p) || (ent.ll == a.b2 && a.t1.Len() == a.p)) {
+		lru := a.t1.Back().Value.(*entry)
+		lru.value = nil
+		lru.setMRU(a.b1)
+	} else {
+		lru := a.t2.Back().Value.(*entry)
+		lru.value = nil
+		lru.setMRU(a.b2)
+	}
+}
+
+func (e *entry) setLRU(list *list.List) {
+	e.detach()
+	e.ll = list
+	e.el = e.ll.PushBack(e)
+}
+
+func (e *entry) setMRU(list *list.List) {
+	e.detach()
+	e.ll = list
+	e.el = e.ll.PushFront(e)
+}
+
+func (e *entry) detach() {
+	if e.ll != nil {
+		e.ll.Remove(e.el)
+	}
+}
diff --git a/trie/cache.go b/trie/cache.go
deleted file mode 100644
index e475fc861..000000000
--- a/trie/cache.go
+++ /dev/null
@@ -1,78 +0,0 @@
-// Copyright 2014 The go-ethereum Authors
-// This file is part of the go-ethereum library.
-//
-// The go-ethereum library is free software: you can redistribute it and/or modify
-// it under the terms of the GNU Lesser General Public License as published by
-// the Free Software Foundation, either version 3 of the License, or
-// (at your option) any later version.
-//
-// The go-ethereum library is distributed in the hope that it will be useful,
-// but WITHOUT ANY WARRANTY; without even the implied warranty of
-// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
-// GNU Lesser General Public License for more details.
-//
-// You should have received a copy of the GNU Lesser General Public License
-// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
-
-package trie
-
-import (
-	"github.com/ethereum/go-ethereum/ethdb"
-	"github.com/ethereum/go-ethereum/logger/glog"
-	"github.com/syndtr/goleveldb/leveldb"
-)
-
-type Backend interface {
-	Get([]byte) ([]byte, error)
-	Put([]byte, []byte) error
-}
-
-type Cache struct {
-	batch   *leveldb.Batch
-	store   map[string][]byte
-	backend Backend
-}
-
-func NewCache(backend Backend) *Cache {
-	return &Cache{new(leveldb.Batch), make(map[string][]byte), backend}
-}
-
-func (self *Cache) Get(key []byte) []byte {
-	data := self.store[string(key)]
-	if data == nil {
-		data, _ = self.backend.Get(key)
-	}
-
-	return data
-}
-
-func (self *Cache) Put(key []byte, data []byte) {
-	self.batch.Put(key, data)
-	self.store[string(key)] = data
-}
-
-// Flush flushes the trie to the backing layer. If this is a leveldb instance
-// we'll use a batched write, otherwise we'll use regular put.
-func (self *Cache) Flush() {
-	if db, ok := self.backend.(*ethdb.LDBDatabase); ok {
-		if err := db.LDB().Write(self.batch, nil); err != nil {
-			glog.Fatal("db write err:", err)
-		}
-	} else {
-		for k, v := range self.store {
-			self.backend.Put([]byte(k), v)
-		}
-	}
-}
-
-func (self *Cache) Copy() *Cache {
-	cache := NewCache(self.backend)
-	for k, v := range self.store {
-		cache.store[k] = v
-	}
-	return cache
-}
-
-func (self *Cache) Reset() {
-	//self.store = make(map[string][]byte)
-}
diff --git a/trie/encoding.go b/trie/encoding.go
index 9c862d78f..3c172b843 100644
--- a/trie/encoding.go
+++ b/trie/encoding.go
@@ -16,34 +16,36 @@
 
 package trie
 
-func CompactEncode(hexSlice []byte) []byte {
-	terminator := 0
+func compactEncode(hexSlice []byte) []byte {
+	terminator := byte(0)
 	if hexSlice[len(hexSlice)-1] == 16 {
 		terminator = 1
-	}
-
-	if terminator == 1 {
 		hexSlice = hexSlice[:len(hexSlice)-1]
 	}
-
-	oddlen := len(hexSlice) % 2
-	flags := byte(2*terminator + oddlen)
-	if oddlen != 0 {
-		hexSlice = append([]byte{flags}, hexSlice...)
-	} else {
-		hexSlice = append([]byte{flags, 0}, hexSlice...)
+	var (
+		odd    = byte(len(hexSlice) % 2)
+		buflen = len(hexSlice)/2 + 1
+		bi, hi = 0, 0    // indices
+		hs     = byte(0) // shift: flips between 0 and 4
+	)
+	if odd == 0 {
+		bi = 1
+		hs = 4
 	}
-
-	l := len(hexSlice) / 2
-	var buf = make([]byte, l)
-	for i := 0; i < l; i++ {
-		buf[i] = 16*hexSlice[2*i] + hexSlice[2*i+1]
+	buf := make([]byte, buflen)
+	buf[0] = terminator<<5 | byte(odd)<<4
+	for bi < len(buf) && hi < len(hexSlice) {
+		buf[bi] |= hexSlice[hi] << hs
+		if hs == 0 {
+			bi++
+		}
+		hi, hs = hi+1, hs^(1<<2)
 	}
 	return buf
 }
 
-func CompactDecode(str []byte) []byte {
-	base := CompactHexDecode(str)
+func compactDecode(str []byte) []byte {
+	base := compactHexDecode(str)
 	base = base[:len(base)-1]
 	if base[0] >= 2 {
 		base = append(base, 16)
@@ -53,11 +55,10 @@ func CompactDecode(str []byte) []byte {
 	} else {
 		base = base[2:]
 	}
-
 	return base
 }
 
-func CompactHexDecode(str []byte) []byte {
+func compactHexDecode(str []byte) []byte {
 	l := len(str)*2 + 1
 	var nibbles = make([]byte, l)
 	for i, b := range str {
@@ -68,7 +69,7 @@ func CompactHexDecode(str []byte) []byte {
 	return nibbles
 }
 
-func DecodeCompact(key []byte) []byte {
+func decodeCompact(key []byte) []byte {
 	l := len(key) / 2
 	var res = make([]byte, l)
 	for i := 0; i < l; i++ {
@@ -77,3 +78,30 @@ func DecodeCompact(key []byte) []byte {
 	}
 	return res
 }
+
+// prefixLen returns the length of the common prefix of a and b.
+func prefixLen(a, b []byte) int {
+	var i, length = 0, len(a)
+	if len(b) < length {
+		length = len(b)
+	}
+	for ; i < length; i++ {
+		if a[i] != b[i] {
+			break
+		}
+	}
+	return i
+}
+
+func hasTerm(s []byte) bool {
+	return s[len(s)-1] == 16
+}
+
+func remTerm(s []byte) []byte {
+	if hasTerm(s) {
+		b := make([]byte, len(s)-1)
+		copy(b, s)
+		return b
+	}
+	return s
+}
diff --git a/trie/encoding_test.go b/trie/encoding_test.go
index e49b57ef0..061d48d58 100644
--- a/trie/encoding_test.go
+++ b/trie/encoding_test.go
@@ -23,7 +23,7 @@ import (
 	checker "gopkg.in/check.v1"
 )
 
-func Test(t *testing.T) { checker.TestingT(t) }
+func TestEncoding(t *testing.T) { checker.TestingT(t) }
 
 type TrieEncodingSuite struct{}
 
@@ -32,64 +32,64 @@ var _ = checker.Suite(&TrieEncodingSuite{})
 func (s *TrieEncodingSuite) TestCompactEncode(c *checker.C) {
 	// even compact encode
 	test1 := []byte{1, 2, 3, 4, 5}
-	res1 := CompactEncode(test1)
+	res1 := compactEncode(test1)
 	c.Assert(res1, checker.DeepEquals, []byte("\x11\x23\x45"))
 
 	// odd compact encode
 	test2 := []byte{0, 1, 2, 3, 4, 5}
-	res2 := CompactEncode(test2)
+	res2 := compactEncode(test2)
 	c.Assert(res2, checker.DeepEquals, []byte("\x00\x01\x23\x45"))
 
 	//odd terminated compact encode
 	test3 := []byte{0, 15, 1, 12, 11, 8 /*term*/, 16}
-	res3 := CompactEncode(test3)
+	res3 := compactEncode(test3)
 	c.Assert(res3, checker.DeepEquals, []byte("\x20\x0f\x1c\xb8"))
 
 	// even terminated compact encode
 	test4 := []byte{15, 1, 12, 11, 8 /*term*/, 16}
-	res4 := CompactEncode(test4)
+	res4 := compactEncode(test4)
 	c.Assert(res4, checker.DeepEquals, []byte("\x3f\x1c\xb8"))
 }
 
 func (s *TrieEncodingSuite) TestCompactHexDecode(c *checker.C) {
 	exp := []byte{7, 6, 6, 5, 7, 2, 6, 2, 16}
-	res := CompactHexDecode([]byte("verb"))
+	res := compactHexDecode([]byte("verb"))
 	c.Assert(res, checker.DeepEquals, exp)
 }
 
 func (s *TrieEncodingSuite) TestCompactDecode(c *checker.C) {
 	// odd compact decode
 	exp := []byte{1, 2, 3, 4, 5}
-	res := CompactDecode([]byte("\x11\x23\x45"))
+	res := compactDecode([]byte("\x11\x23\x45"))
 	c.Assert(res, checker.DeepEquals, exp)
 
 	// even compact decode
 	exp = []byte{0, 1, 2, 3, 4, 5}
-	res = CompactDecode([]byte("\x00\x01\x23\x45"))
+	res = compactDecode([]byte("\x00\x01\x23\x45"))
 	c.Assert(res, checker.DeepEquals, exp)
 
 	// even terminated compact decode
 	exp = []byte{0, 15, 1, 12, 11, 8 /*term*/, 16}
-	res = CompactDecode([]byte("\x20\x0f\x1c\xb8"))
+	res = compactDecode([]byte("\x20\x0f\x1c\xb8"))
 	c.Assert(res, checker.DeepEquals, exp)
 
 	// even terminated compact decode
 	exp = []byte{15, 1, 12, 11, 8 /*term*/, 16}
-	res = CompactDecode([]byte("\x3f\x1c\xb8"))
+	res = compactDecode([]byte("\x3f\x1c\xb8"))
 	c.Assert(res, checker.DeepEquals, exp)
 }
 
 func (s *TrieEncodingSuite) TestDecodeCompact(c *checker.C) {
 	exp, _ := hex.DecodeString("012345")
-	res := DecodeCompact([]byte{0, 1, 2, 3, 4, 5})
+	res := decodeCompact([]byte{0, 1, 2, 3, 4, 5})
 	c.Assert(res, checker.DeepEquals, exp)
 
 	exp, _ = hex.DecodeString("012345")
-	res = DecodeCompact([]byte{0, 1, 2, 3, 4, 5, 16})
+	res = decodeCompact([]byte{0, 1, 2, 3, 4, 5, 16})
 	c.Assert(res, checker.DeepEquals, exp)
 
 	exp, _ = hex.DecodeString("abcdef")
-	res = DecodeCompact([]byte{10, 11, 12, 13, 14, 15})
+	res = decodeCompact([]byte{10, 11, 12, 13, 14, 15})
 	c.Assert(res, checker.DeepEquals, exp)
 }
 
@@ -97,29 +97,27 @@ func BenchmarkCompactEncode(b *testing.B) {
 
 	testBytes := []byte{0, 15, 1, 12, 11, 8 /*term*/, 16}
 	for i := 0; i < b.N; i++ {
-		CompactEncode(testBytes)
+		compactEncode(testBytes)
 	}
 }
 
 func BenchmarkCompactDecode(b *testing.B) {
 	testBytes := []byte{0, 15, 1, 12, 11, 8 /*term*/, 16}
 	for i := 0; i < b.N; i++ {
-		CompactDecode(testBytes)
+		compactDecode(testBytes)
 	}
 }
 
 func BenchmarkCompactHexDecode(b *testing.B) {
 	testBytes := []byte{7, 6, 6, 5, 7, 2, 6, 2, 16}
 	for i := 0; i < b.N; i++ {
-		CompactHexDecode(testBytes)
+		compactHexDecode(testBytes)
 	}
-
 }
 
 func BenchmarkDecodeCompact(b *testing.B) {
 	testBytes := []byte{7, 6, 6, 5, 7, 2, 6, 2, 16}
 	for i := 0; i < b.N; i++ {
-		DecodeCompact(testBytes)
+		decodeCompact(testBytes)
 	}
-
 }
diff --git a/trie/fullnode.go b/trie/fullnode.go
deleted file mode 100644
index 8ff019ec4..000000000
--- a/trie/fullnode.go
+++ /dev/null
@@ -1,94 +0,0 @@
-// Copyright 2014 The go-ethereum Authors
-// This file is part of the go-ethereum library.
-//
-// The go-ethereum library is free software: you can redistribute it and/or modify
-// it under the terms of the GNU Lesser General Public License as published by
-// the Free Software Foundation, either version 3 of the License, or
-// (at your option) any later version.
-//
-// The go-ethereum library is distributed in the hope that it will be useful,
-// but WITHOUT ANY WARRANTY; without even the implied warranty of
-// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
-// GNU Lesser General Public License for more details.
-//
-// You should have received a copy of the GNU Lesser General Public License
-// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
-
-package trie
-
-type FullNode struct {
-	trie  *Trie
-	nodes [17]Node
-	dirty bool
-}
-
-func NewFullNode(t *Trie) *FullNode {
-	return &FullNode{trie: t}
-}
-
-func (self *FullNode) Dirty() bool { return self.dirty }
-func (self *FullNode) Value() Node {
-	self.nodes[16] = self.trie.trans(self.nodes[16])
-	return self.nodes[16]
-}
-func (self *FullNode) Branches() []Node {
-	return self.nodes[:16]
-}
-
-func (self *FullNode) Copy(t *Trie) Node {
-	nnode := NewFullNode(t)
-	for i, node := range self.nodes {
-		if node != nil {
-			nnode.nodes[i] = node
-		}
-	}
-	nnode.dirty = true
-
-	return nnode
-}
-
-// Returns the length of non-nil nodes
-func (self *FullNode) Len() (amount int) {
-	for _, node := range self.nodes {
-		if node != nil {
-			amount++
-		}
-	}
-
-	return
-}
-
-func (self *FullNode) Hash() interface{} {
-	return self.trie.store(self)
-}
-
-func (self *FullNode) RlpData() interface{} {
-	t := make([]interface{}, 17)
-	for i, node := range self.nodes {
-		if node != nil {
-			t[i] = node.Hash()
-		} else {
-			t[i] = ""
-		}
-	}
-
-	return t
-}
-
-func (self *FullNode) set(k byte, value Node) {
-	self.nodes[int(k)] = value
-	self.dirty = true
-}
-
-func (self *FullNode) branch(i byte) Node {
-	if self.nodes[int(i)] != nil {
-		self.nodes[int(i)] = self.trie.trans(self.nodes[int(i)])
-
-		return self.nodes[int(i)]
-	}
-	return nil
-}
-
-func (self *FullNode) setDirty(dirty bool) {
-	self.dirty = dirty
-}
diff --git a/trie/hashnode.go b/trie/hashnode.go
deleted file mode 100644
index d4a0bc7ec..000000000
--- a/trie/hashnode.go
+++ /dev/null
@@ -1,46 +0,0 @@
-// Copyright 2014 The go-ethereum Authors
-// This file is part of the go-ethereum library.
-//
-// The go-ethereum library is free software: you can redistribute it and/or modify
-// it under the terms of the GNU Lesser General Public License as published by
-// the Free Software Foundation, either version 3 of the License, or
-// (at your option) any later version.
-//
-// The go-ethereum library is distributed in the hope that it will be useful,
-// but WITHOUT ANY WARRANTY; without even the implied warranty of
-// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
-// GNU Lesser General Public License for more details.
-//
-// You should have received a copy of the GNU Lesser General Public License
-// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
-
-package trie
-
-import "github.com/ethereum/go-ethereum/common"
-
-type HashNode struct {
-	key   []byte
-	trie  *Trie
-	dirty bool
-}
-
-func NewHash(key []byte, trie *Trie) *HashNode {
-	return &HashNode{key, trie, false}
-}
-
-func (self *HashNode) RlpData() interface{} {
-	return self.key
-}
-
-func (self *HashNode) Hash() interface{} {
-	return self.key
-}
-
-func (self *HashNode) setDirty(dirty bool) {
-	self.dirty = dirty
-}
-
-// These methods will never be called but we have to satisfy Node interface
-func (self *HashNode) Value() Node       { return nil }
-func (self *HashNode) Dirty() bool       { return true }
-func (self *HashNode) Copy(t *Trie) Node { return NewHash(common.CopyBytes(self.key), t) }
diff --git a/trie/iterator.go b/trie/iterator.go
index 9c4c7fbe5..38555fe08 100644
--- a/trie/iterator.go
+++ b/trie/iterator.go
@@ -16,9 +16,7 @@
 
 package trie
 
-import (
-	"bytes"
-)
+import "bytes"
 
 type Iterator struct {
 	trie *Trie
@@ -32,32 +30,29 @@ func NewIterator(trie *Trie) *Iterator {
 }
 
 func (self *Iterator) Next() bool {
-	self.trie.mu.Lock()
-	defer self.trie.mu.Unlock()
-
 	isIterStart := false
 	if self.Key == nil {
 		isIterStart = true
 		self.Key = make([]byte, 32)
 	}
 
-	key := RemTerm(CompactHexDecode(self.Key))
+	key := remTerm(compactHexDecode(self.Key))
 	k := self.next(self.trie.root, key, isIterStart)
 
-	self.Key = []byte(DecodeCompact(k))
+	self.Key = []byte(decodeCompact(k))
 
 	return len(k) > 0
 }
 
-func (self *Iterator) next(node Node, key []byte, isIterStart bool) []byte {
+func (self *Iterator) next(node interface{}, key []byte, isIterStart bool) []byte {
 	if node == nil {
 		return nil
 	}
 
 	switch node := node.(type) {
-	case *FullNode:
+	case fullNode:
 		if len(key) > 0 {
-			k := self.next(node.branch(key[0]), key[1:], isIterStart)
+			k := self.next(node[key[0]], key[1:], isIterStart)
 			if k != nil {
 				return append([]byte{key[0]}, k...)
 			}
@@ -69,31 +64,31 @@ func (self *Iterator) next(node Node, key []byte, isIterStart bool) []byte {
 		}
 
 		for i := r; i < 16; i++ {
-			k := self.key(node.branch(byte(i)))
+			k := self.key(node[i])
 			if k != nil {
 				return append([]byte{i}, k...)
 			}
 		}
 
-	case *ShortNode:
-		k := RemTerm(node.Key())
-		if vnode, ok := node.Value().(*ValueNode); ok {
+	case shortNode:
+		k := remTerm(node.Key)
+		if vnode, ok := node.Val.(valueNode); ok {
 			switch bytes.Compare([]byte(k), key) {
 			case 0:
 				if isIterStart {
-					self.Value = vnode.Val()
+					self.Value = vnode
 					return k
 				}
 			case 1:
-				self.Value = vnode.Val()
+				self.Value = vnode
 				return k
 			}
 		} else {
-			cnode := node.Value()
+			cnode := node.Val
 
 			var ret []byte
 			skey := key[len(k):]
-			if BeginsWith(key, k) {
+			if bytes.HasPrefix(key, k) {
 				ret = self.next(cnode, skey, isIterStart)
 			} else if bytes.Compare(k, key[:len(k)]) > 0 {
 				return self.key(node)
@@ -103,37 +98,36 @@ func (self *Iterator) next(node Node, key []byte, isIterStart bool) []byte {
 				return append(k, ret...)
 			}
 		}
-	}
 
+	case hashNode:
+		return self.next(self.trie.resolveHash(node), key, isIterStart)
+	}
 	return nil
 }
 
-func (self *Iterator) key(node Node) []byte {
+func (self *Iterator) key(node interface{}) []byte {
 	switch node := node.(type) {
-	case *ShortNode:
+	case shortNode:
 		// Leaf node
-		if vnode, ok := node.Value().(*ValueNode); ok {
-			k := RemTerm(node.Key())
-			self.Value = vnode.Val()
-
+		k := remTerm(node.Key)
+		if vnode, ok := node.Val.(valueNode); ok {
+			self.Value = vnode
 			return k
-		} else {
-			k := RemTerm(node.Key())
-			return append(k, self.key(node.Value())...)
 		}
-	case *FullNode:
-		if node.Value() != nil {
-			self.Value = node.Value().(*ValueNode).Val()
-
+		return append(k, self.key(node.Val)...)
+	case fullNode:
+		if node[16] != nil {
+			self.Value = node[16].(valueNode)
 			return []byte{16}
 		}
-
 		for i := 0; i < 16; i++ {
-			k := self.key(node.branch(byte(i)))
+			k := self.key(node[i])
 			if k != nil {
 				return append([]byte{byte(i)}, k...)
 			}
 		}
+	case hashNode:
+		return self.key(self.trie.resolveHash(node))
 	}
 
 	return nil
diff --git a/trie/iterator_test.go b/trie/iterator_test.go
index 148f9adf9..fdc60b412 100644
--- a/trie/iterator_test.go
+++ b/trie/iterator_test.go
@@ -19,7 +19,7 @@ package trie
 import "testing"
 
 func TestIterator(t *testing.T) {
-	trie := NewEmpty()
+	trie := newEmpty()
 	vals := []struct{ k, v string }{
 		{"do", "verb"},
 		{"ether", "wookiedoo"},
@@ -32,11 +32,11 @@ func TestIterator(t *testing.T) {
 	v := make(map[string]bool)
 	for _, val := range vals {
 		v[val.k] = false
-		trie.UpdateString(val.k, val.v)
+		trie.Update([]byte(val.k), []byte(val.v))
 	}
 	trie.Commit()
 
-	it := trie.Iterator()
+	it := NewIterator(trie)
 	for it.Next() {
 		v[string(it.Key)] = true
 	}
diff --git a/trie/node.go b/trie/node.go
index 9d49029de..0bfa21dc4 100644
--- a/trie/node.go
+++ b/trie/node.go
@@ -16,46 +16,172 @@
 
 package trie
 
-import "fmt"
+import (
+	"fmt"
+	"io"
+	"strings"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/rlp"
+)
 
 var indices = []string{"0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "a", "b", "c", "d", "e", "f", "[17]"}
 
-type Node interface {
-	Value() Node
-	Copy(*Trie) Node // All nodes, for now, return them self
-	Dirty() bool
+type node interface {
 	fstring(string) string
-	Hash() interface{}
-	RlpData() interface{}
-	setDirty(dirty bool)
 }
 
-// Value node
-func (self *ValueNode) String() string            { return self.fstring("") }
-func (self *FullNode) String() string             { return self.fstring("") }
-func (self *ShortNode) String() string            { return self.fstring("") }
-func (self *ValueNode) fstring(ind string) string { return fmt.Sprintf("%x ", self.data) }
+type (
+	fullNode  [17]node
+	shortNode struct {
+		Key []byte
+		Val node
+	}
+	hashNode  []byte
+	valueNode []byte
+)
 
-//func (self *HashNode) fstring(ind string) string  { return fmt.Sprintf("< %x > ", self.key) }
-func (self *HashNode) fstring(ind string) string {
-	return fmt.Sprintf("%v", self.trie.trans(self))
-}
+// Pretty printing.
+func (n fullNode) String() string  { return n.fstring("") }
+func (n shortNode) String() string { return n.fstring("") }
+func (n hashNode) String() string  { return n.fstring("") }
+func (n valueNode) String() string { return n.fstring("") }
 
-// Full node
-func (self *FullNode) fstring(ind string) string {
+func (n fullNode) fstring(ind string) string {
 	resp := fmt.Sprintf("[\n%s  ", ind)
-	for i, node := range self.nodes {
+	for i, node := range n {
 		if node == nil {
 			resp += fmt.Sprintf("%s: <nil> ", indices[i])
 		} else {
 			resp += fmt.Sprintf("%s: %v", indices[i], node.fstring(ind+"  "))
 		}
 	}
-
 	return resp + fmt.Sprintf("\n%s] ", ind)
 }
+func (n shortNode) fstring(ind string) string {
+	return fmt.Sprintf("{%x: %v} ", n.Key, n.Val.fstring(ind+"  "))
+}
+func (n hashNode) fstring(ind string) string {
+	return fmt.Sprintf("<%x> ", []byte(n))
+}
+func (n valueNode) fstring(ind string) string {
+	return fmt.Sprintf("%x ", []byte(n))
+}
+
+func mustDecodeNode(dbkey, buf []byte) node {
+	n, err := decodeNode(buf)
+	if err != nil {
+		panic(fmt.Sprintf("node %x: %v", dbkey, err))
+	}
+	return n
+}
+
+// decodeNode parses the RLP encoding of a trie node.
+func decodeNode(buf []byte) (node, error) {
+	if len(buf) == 0 {
+		return nil, io.ErrUnexpectedEOF
+	}
+	elems, _, err := rlp.SplitList(buf)
+	if err != nil {
+		return nil, fmt.Errorf("decode error: %v", err)
+	}
+	switch c, _ := rlp.CountValues(elems); c {
+	case 2:
+		n, err := decodeShort(elems)
+		return n, wrapError(err, "short")
+	case 17:
+		n, err := decodeFull(elems)
+		return n, wrapError(err, "full")
+	default:
+		return nil, fmt.Errorf("invalid number of list elements: %v", c)
+	}
+}
+
+func decodeShort(buf []byte) (node, error) {
+	kbuf, rest, err := rlp.SplitString(buf)
+	if err != nil {
+		return nil, err
+	}
+	key := compactDecode(kbuf)
+	if key[len(key)-1] == 16 {
+		// value node
+		val, _, err := rlp.SplitString(rest)
+		if err != nil {
+			return nil, fmt.Errorf("invalid value node: %v", err)
+		}
+		return shortNode{key, valueNode(val)}, nil
+	}
+	r, _, err := decodeRef(rest)
+	if err != nil {
+		return nil, wrapError(err, "val")
+	}
+	return shortNode{key, r}, nil
+}
+
+func decodeFull(buf []byte) (fullNode, error) {
+	var n fullNode
+	for i := 0; i < 16; i++ {
+		cld, rest, err := decodeRef(buf)
+		if err != nil {
+			return n, wrapError(err, fmt.Sprintf("[%d]", i))
+		}
+		n[i], buf = cld, rest
+	}
+	val, _, err := rlp.SplitString(buf)
+	if err != nil {
+		return n, err
+	}
+	if len(val) > 0 {
+		n[16] = valueNode(val)
+	}
+	return n, nil
+}
+
+const hashLen = len(common.Hash{})
+
+func decodeRef(buf []byte) (node, []byte, error) {
+	kind, val, rest, err := rlp.Split(buf)
+	if err != nil {
+		return nil, buf, err
+	}
+	switch {
+	case kind == rlp.List:
+		// 'embedded' node reference. The encoding must be smaller
+		// than a hash in order to be valid.
+		if size := len(buf) - len(rest); size > hashLen {
+			err := fmt.Errorf("oversized embedded node (size is %d bytes, want size < %d)", size, hashLen)
+			return nil, buf, err
+		}
+		n, err := decodeNode(buf)
+		return n, rest, err
+	case kind == rlp.String && len(val) == 0:
+		// empty node
+		return nil, rest, nil
+	case kind == rlp.String && len(val) == 32:
+		return hashNode(val), rest, nil
+	default:
+		return nil, nil, fmt.Errorf("invalid RLP string size %d (want 0 or 32)", len(val))
+	}
+}
+
+// wraps a decoding error with information about the path to the
+// invalid child node (for debugging encoding issues).
+type decodeError struct {
+	what  error
+	stack []string
+}
+
+func wrapError(err error, ctx string) error {
+	if err == nil {
+		return nil
+	}
+	if decErr, ok := err.(*decodeError); ok {
+		decErr.stack = append(decErr.stack, ctx)
+		return decErr
+	}
+	return &decodeError{err, []string{ctx}}
+}
 
-// Short node
-func (self *ShortNode) fstring(ind string) string {
-	return fmt.Sprintf("[ %x: %v ] ", self.key, self.value.fstring(ind+"  "))
+func (err *decodeError) Error() string {
+	return fmt.Sprintf("%v (decode path: %s)", err.what, strings.Join(err.stack, "<-"))
 }
diff --git a/trie/proof.go b/trie/proof.go
new file mode 100644
index 000000000..a705c49db
--- /dev/null
+++ b/trie/proof.go
@@ -0,0 +1,122 @@
+package trie
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/crypto/sha3"
+	"github.com/ethereum/go-ethereum/rlp"
+)
+
+// Prove constructs a merkle proof for key. The result contains all
+// encoded nodes on the path to the value at key. The value itself is
+// also included in the last node and can be retrieved by verifying
+// the proof.
+//
+// The returned proof is nil if the trie does not contain a value for key.
+// For existing keys, the proof will have at least one element.
+func (t *Trie) Prove(key []byte) []rlp.RawValue {
+	// Collect all nodes on the path to key.
+	key = compactHexDecode(key)
+	nodes := []node{}
+	tn := t.root
+	for len(key) > 0 {
+		switch n := tn.(type) {
+		case shortNode:
+			if len(key) < len(n.Key) || !bytes.Equal(n.Key, key[:len(n.Key)]) {
+				// The trie doesn't contain the key.
+				return nil
+			}
+			tn = n.Val
+			key = key[len(n.Key):]
+			nodes = append(nodes, n)
+		case fullNode:
+			tn = n[key[0]]
+			key = key[1:]
+			nodes = append(nodes, n)
+		case nil:
+			return nil
+		case hashNode:
+			tn = t.resolveHash(n)
+		default:
+			panic(fmt.Sprintf("%T: invalid node: %v", tn, tn))
+		}
+	}
+	if t.hasher == nil {
+		t.hasher = newHasher()
+	}
+	proof := make([]rlp.RawValue, 0, len(nodes))
+	for i, n := range nodes {
+		// Don't bother checking for errors here since hasher panics
+		// if encoding doesn't work and we're not writing to any database.
+		n, _ = t.hasher.replaceChildren(n, nil)
+		hn, _ := t.hasher.store(n, nil, false)
+		if _, ok := hn.(hashNode); ok || i == 0 {
+			// If the node's database encoding is a hash (or is the
+			// root node), it becomes a proof element.
+			enc, _ := rlp.EncodeToBytes(n)
+			proof = append(proof, enc)
+		}
+	}
+	return proof
+}
+
+// VerifyProof checks merkle proofs. The given proof must contain the
+// value for key in a trie with the given root hash. VerifyProof
+// returns an error if the proof contains invalid trie nodes or the
+// wrong value.
+func VerifyProof(rootHash common.Hash, key []byte, proof []rlp.RawValue) (value []byte, err error) {
+	key = compactHexDecode(key)
+	sha := sha3.NewKeccak256()
+	wantHash := rootHash.Bytes()
+	for i, buf := range proof {
+		sha.Reset()
+		sha.Write(buf)
+		if !bytes.Equal(sha.Sum(nil), wantHash) {
+			return nil, fmt.Errorf("bad proof node %d: hash mismatch", i)
+		}
+		n, err := decodeNode(buf)
+		if err != nil {
+			return nil, fmt.Errorf("bad proof node %d: %v", i, err)
+		}
+		keyrest, cld := get(n, key)
+		switch cld := cld.(type) {
+		case nil:
+			return nil, fmt.Errorf("key mismatch at proof node %d", i)
+		case hashNode:
+			key = keyrest
+			wantHash = cld
+		case valueNode:
+			if i != len(proof)-1 {
+				return nil, errors.New("additional nodes at end of proof")
+			}
+			return cld, nil
+		}
+	}
+	return nil, errors.New("unexpected end of proof")
+}
+
+func get(tn node, key []byte) ([]byte, node) {
+	for len(key) > 0 {
+		switch n := tn.(type) {
+		case shortNode:
+			if len(key) < len(n.Key) || !bytes.Equal(n.Key, key[:len(n.Key)]) {
+				return nil, nil
+			}
+			tn = n.Val
+			key = key[len(n.Key):]
+		case fullNode:
+			tn = n[key[0]]
+			key = key[1:]
+		case hashNode:
+			return key, n
+		case nil:
+			return key, nil
+		default:
+			panic(fmt.Sprintf("%T: invalid node: %v", tn, tn))
+		}
+	}
+	return nil, tn.(valueNode)
+}
diff --git a/trie/proof_test.go b/trie/proof_test.go
new file mode 100644
index 000000000..6b5bef05c
--- /dev/null
+++ b/trie/proof_test.go
@@ -0,0 +1,139 @@
+package trie
+
+import (
+	"bytes"
+	crand "crypto/rand"
+	mrand "math/rand"
+	"testing"
+	"time"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/rlp"
+)
+
+func init() {
+	mrand.Seed(time.Now().Unix())
+}
+
+func TestProof(t *testing.T) {
+	trie, vals := randomTrie(500)
+	root := trie.Hash()
+	for _, kv := range vals {
+		proof := trie.Prove(kv.k)
+		if proof == nil {
+			t.Fatalf("missing key %x while constructing proof", kv.k)
+		}
+		val, err := VerifyProof(root, kv.k, proof)
+		if err != nil {
+			t.Fatalf("VerifyProof error for key %x: %v\nraw proof: %x", kv.k, err, proof)
+		}
+		if !bytes.Equal(val, kv.v) {
+			t.Fatalf("VerifyProof returned wrong value for key %x: got %x, want %x", kv.k, val, kv.v)
+		}
+	}
+}
+
+func TestOneElementProof(t *testing.T) {
+	trie := new(Trie)
+	updateString(trie, "k", "v")
+	proof := trie.Prove([]byte("k"))
+	if proof == nil {
+		t.Fatal("nil proof")
+	}
+	if len(proof) != 1 {
+		t.Error("proof should have one element")
+	}
+	val, err := VerifyProof(trie.Hash(), []byte("k"), proof)
+	if err != nil {
+		t.Fatalf("VerifyProof error: %v\nraw proof: %x", err, proof)
+	}
+	if !bytes.Equal(val, []byte("v")) {
+		t.Fatalf("VerifyProof returned wrong value: got %x, want 'k'", val)
+	}
+}
+
+func TestVerifyBadProof(t *testing.T) {
+	trie, vals := randomTrie(800)
+	root := trie.Hash()
+	for _, kv := range vals {
+		proof := trie.Prove(kv.k)
+		if proof == nil {
+			t.Fatal("nil proof")
+		}
+		mutateByte(proof[mrand.Intn(len(proof))])
+		if _, err := VerifyProof(root, kv.k, proof); err == nil {
+			t.Fatalf("expected proof to fail for key %x", kv.k)
+		}
+	}
+}
+
+// mutateByte changes one byte in b.
+func mutateByte(b []byte) {
+	for r := mrand.Intn(len(b)); ; {
+		new := byte(mrand.Intn(255))
+		if new != b[r] {
+			b[r] = new
+			break
+		}
+	}
+}
+
+func BenchmarkProve(b *testing.B) {
+	trie, vals := randomTrie(100)
+	var keys []string
+	for k := range vals {
+		keys = append(keys, k)
+	}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		kv := vals[keys[i%len(keys)]]
+		if trie.Prove(kv.k) == nil {
+			b.Fatalf("nil proof for %x", kv.k)
+		}
+	}
+}
+
+func BenchmarkVerifyProof(b *testing.B) {
+	trie, vals := randomTrie(100)
+	root := trie.Hash()
+	var keys []string
+	var proofs [][]rlp.RawValue
+	for k := range vals {
+		keys = append(keys, k)
+		proofs = append(proofs, trie.Prove([]byte(k)))
+	}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		im := i % len(keys)
+		if _, err := VerifyProof(root, []byte(keys[im]), proofs[im]); err != nil {
+			b.Fatalf("key %x: error", keys[im], err)
+		}
+	}
+}
+
+func randomTrie(n int) (*Trie, map[string]*kv) {
+	trie := new(Trie)
+	vals := make(map[string]*kv)
+	for i := byte(0); i < 100; i++ {
+		value := &kv{common.LeftPadBytes([]byte{i}, 32), []byte{i}, false}
+		value2 := &kv{common.LeftPadBytes([]byte{i + 10}, 32), []byte{i}, false}
+		trie.Update(value.k, value.v)
+		trie.Update(value2.k, value2.v)
+		vals[string(value.k)] = value
+		vals[string(value2.k)] = value2
+	}
+	for i := 0; i < n; i++ {
+		value := &kv{randBytes(32), randBytes(20), false}
+		trie.Update(value.k, value.v)
+		vals[string(value.k)] = value
+	}
+	return trie, vals
+}
+
+func randBytes(n int) []byte {
+	r := make([]byte, n)
+	crand.Read(r)
+	return r
+}
diff --git a/trie/secure_trie.go b/trie/secure_trie.go
index 47c7542bb..47d1934d0 100644
--- a/trie/secure_trie.go
+++ b/trie/secure_trie.go
@@ -16,46 +16,93 @@
 
 package trie
 
-import "github.com/ethereum/go-ethereum/crypto"
+import (
+	"hash"
 
-var keyPrefix = []byte("secure-key-")
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/crypto/sha3"
+)
 
+var secureKeyPrefix = []byte("secure-key-")
+
+// SecureTrie wraps a trie with key hashing. In a secure trie, all
+// access operations hash the key using keccak256. This prevents
+// calling code from creating long chains of nodes that
+// increase the access time.
+//
+// Contrary to a regular trie, a SecureTrie can only be created with
+// New and must have an attached database. The database also stores
+// the preimage of each key.
+//
+// SecureTrie is not safe for concurrent use.
 type SecureTrie struct {
 	*Trie
-}
 
-func NewSecure(root []byte, backend Backend) *SecureTrie {
-	return &SecureTrie{New(root, backend)}
+	hash       hash.Hash
+	secKeyBuf  []byte
+	hashKeyBuf []byte
 }
 
-func (self *SecureTrie) Update(key, value []byte) Node {
-	shaKey := crypto.Sha3(key)
-	self.Trie.cache.Put(append(keyPrefix, shaKey...), key)
-
-	return self.Trie.Update(shaKey, value)
-}
-func (self *SecureTrie) UpdateString(key, value string) Node {
-	return self.Update([]byte(key), []byte(value))
+// NewSecure creates a trie with an existing root node from db.
+//
+// If root is the zero hash or the sha3 hash of an empty string, the
+// trie is initially empty. Otherwise, New will panics if db is nil
+// and returns ErrMissingRoot if the root node cannpt be found.
+// Accessing the trie loads nodes from db on demand.
+func NewSecure(root common.Hash, db Database) (*SecureTrie, error) {
+	if db == nil {
+		panic("NewSecure called with nil database")
+	}
+	trie, err := New(root, db)
+	if err != nil {
+		return nil, err
+	}
+	return &SecureTrie{Trie: trie}, nil
 }
 
-func (self *SecureTrie) Get(key []byte) []byte {
-	return self.Trie.Get(crypto.Sha3(key))
+// Get returns the value for key stored in the trie.
+// The value bytes must not be modified by the caller.
+func (t *SecureTrie) Get(key []byte) []byte {
+	return t.Trie.Get(t.hashKey(key))
 }
-func (self *SecureTrie) GetString(key string) []byte {
-	return self.Get([]byte(key))
+
+// Update associates key with value in the trie. Subsequent calls to
+// Get will return value. If value has length zero, any existing value
+// is deleted from the trie and calls to Get will return nil.
+//
+// The value bytes must not be modified by the caller while they are
+// stored in the trie.
+func (t *SecureTrie) Update(key, value []byte) {
+	hk := t.hashKey(key)
+	t.Trie.Update(hk, value)
+	t.Trie.db.Put(t.secKey(hk), key)
 }
 
-func (self *SecureTrie) Delete(key []byte) Node {
-	return self.Trie.Delete(crypto.Sha3(key))
+// Delete removes any existing value for key from the trie.
+func (t *SecureTrie) Delete(key []byte) {
+	t.Trie.Delete(t.hashKey(key))
 }
-func (self *SecureTrie) DeleteString(key string) Node {
-	return self.Delete([]byte(key))
+
+// GetKey returns the sha3 preimage of a hashed key that was
+// previously used to store a value.
+func (t *SecureTrie) GetKey(shaKey []byte) []byte {
+	key, _ := t.Trie.db.Get(t.secKey(shaKey))
+	return key
 }
 
-func (self *SecureTrie) Copy() *SecureTrie {
-	return &SecureTrie{self.Trie.Copy()}
+func (t *SecureTrie) secKey(key []byte) []byte {
+	t.secKeyBuf = append(t.secKeyBuf[:0], secureKeyPrefix...)
+	t.secKeyBuf = append(t.secKeyBuf, key...)
+	return t.secKeyBuf
 }
 
-func (self *SecureTrie) GetKey(shaKey []byte) []byte {
-	return self.Trie.cache.Get(append(keyPrefix, shaKey...))
+func (t *SecureTrie) hashKey(key []byte) []byte {
+	if t.hash == nil {
+		t.hash = sha3.NewKeccak256()
+		t.hashKeyBuf = make([]byte, 32)
+	}
+	t.hash.Reset()
+	t.hash.Write(key)
+	t.hashKeyBuf = t.hash.Sum(t.hashKeyBuf[:0])
+	return t.hashKeyBuf
 }
diff --git a/trie/secure_trie_test.go b/trie/secure_trie_test.go
new file mode 100644
index 000000000..13c6cd02e
--- /dev/null
+++ b/trie/secure_trie_test.go
@@ -0,0 +1,74 @@
+// Copyright 2015 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package trie
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/crypto"
+	"github.com/ethereum/go-ethereum/ethdb"
+)
+
+func newEmptySecure() *SecureTrie {
+	db, _ := ethdb.NewMemDatabase()
+	trie, _ := NewSecure(common.Hash{}, db)
+	return trie
+}
+
+func TestSecureDelete(t *testing.T) {
+	trie := newEmptySecure()
+	vals := []struct{ k, v string }{
+		{"do", "verb"},
+		{"ether", "wookiedoo"},
+		{"horse", "stallion"},
+		{"shaman", "horse"},
+		{"doge", "coin"},
+		{"ether", ""},
+		{"dog", "puppy"},
+		{"shaman", ""},
+	}
+	for _, val := range vals {
+		if val.v != "" {
+			trie.Update([]byte(val.k), []byte(val.v))
+		} else {
+			trie.Delete([]byte(val.k))
+		}
+	}
+	hash := trie.Hash()
+	exp := common.HexToHash("29b235a58c3c25ab83010c327d5932bcf05324b7d6b1185e650798034783ca9d")
+	if hash != exp {
+		t.Errorf("expected %x got %x", exp, hash)
+	}
+}
+
+func TestSecureGetKey(t *testing.T) {
+	trie := newEmptySecure()
+	trie.Update([]byte("foo"), []byte("bar"))
+
+	key := []byte("foo")
+	value := []byte("bar")
+	seckey := crypto.Sha3(key)
+
+	if !bytes.Equal(trie.Get(key), value) {
+		t.Errorf("Get did not return bar")
+	}
+	if k := trie.GetKey(seckey); !bytes.Equal(k, key) {
+		t.Errorf("GetKey returned %q, want %q", k, key)
+	}
+}
diff --git a/trie/shortnode.go b/trie/shortnode.go
deleted file mode 100644
index 569d5f109..000000000
--- a/trie/shortnode.go
+++ /dev/null
@@ -1,57 +0,0 @@
-// Copyright 2014 The go-ethereum Authors
-// This file is part of the go-ethereum library.
-//
-// The go-ethereum library is free software: you can redistribute it and/or modify
-// it under the terms of the GNU Lesser General Public License as published by
-// the Free Software Foundation, either version 3 of the License, or
-// (at your option) any later version.
-//
-// The go-ethereum library is distributed in the hope that it will be useful,
-// but WITHOUT ANY WARRANTY; without even the implied warranty of
-// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
-// GNU Lesser General Public License for more details.
-//
-// You should have received a copy of the GNU Lesser General Public License
-// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
-
-package trie
-
-import "github.com/ethereum/go-ethereum/common"
-
-type ShortNode struct {
-	trie  *Trie
-	key   []byte
-	value Node
-	dirty bool
-}
-
-func NewShortNode(t *Trie, key []byte, value Node) *ShortNode {
-	return &ShortNode{t, CompactEncode(key), value, false}
-}
-func (self *ShortNode) Value() Node {
-	self.value = self.trie.trans(self.value)
-
-	return self.value
-}
-func (self *ShortNode) Dirty() bool { return self.dirty }
-func (self *ShortNode) Copy(t *Trie) Node {
-	node := &ShortNode{t, nil, self.value.Copy(t), self.dirty}
-	node.key = common.CopyBytes(self.key)
-	node.dirty = true
-	return node
-}
-
-func (self *ShortNode) RlpData() interface{} {
-	return []interface{}{self.key, self.value.Hash()}
-}
-func (self *ShortNode) Hash() interface{} {
-	return self.trie.store(self)
-}
-
-func (self *ShortNode) Key() []byte {
-	return CompactDecode(self.key)
-}
-
-func (self *ShortNode) setDirty(dirty bool) {
-	self.dirty = dirty
-}
diff --git a/trie/slice.go b/trie/slice.go
deleted file mode 100644
index ccefbd064..000000000
--- a/trie/slice.go
+++ /dev/null
@@ -1,69 +0,0 @@
-// Copyright 2014 The go-ethereum Authors
-// This file is part of the go-ethereum library.
-//
-// The go-ethereum library is free software: you can redistribute it and/or modify
-// it under the terms of the GNU Lesser General Public License as published by
-// the Free Software Foundation, either version 3 of the License, or
-// (at your option) any later version.
-//
-// The go-ethereum library is distributed in the hope that it will be useful,
-// but WITHOUT ANY WARRANTY; without even the implied warranty of
-// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
-// GNU Lesser General Public License for more details.
-//
-// You should have received a copy of the GNU Lesser General Public License
-// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
-
-package trie
-
-import (
-	"bytes"
-	"math"
-)
-
-// Helper function for comparing slices
-func CompareIntSlice(a, b []int) bool {
-	if len(a) != len(b) {
-		return false
-	}
-	for i, v := range a {
-		if v != b[i] {
-			return false
-		}
-	}
-	return true
-}
-
-// Returns the amount of nibbles that match each other from 0 ...
-func MatchingNibbleLength(a, b []byte) int {
-	var i, length = 0, int(math.Min(float64(len(a)), float64(len(b))))
-
-	for i < length {
-		if a[i] != b[i] {
-			break
-		}
-		i++
-	}
-
-	return i
-}
-
-func HasTerm(s []byte) bool {
-	return s[len(s)-1] == 16
-}
-
-func RemTerm(s []byte) []byte {
-	if HasTerm(s) {
-		return s[:len(s)-1]
-	}
-
-	return s
-}
-
-func BeginsWith(a, b []byte) bool {
-	if len(b) > len(a) {
-		return false
-	}
-
-	return bytes.Equal(a[:len(b)], b)
-}
diff --git a/trie/trie.go b/trie/trie.go
index abf48a850..aa8d39fe2 100644
--- a/trie/trie.go
+++ b/trie/trie.go
@@ -19,372 +19,425 @@ package trie
 
 import (
 	"bytes"
-	"container/list"
+	"errors"
 	"fmt"
-	"sync"
+	"hash"
 
 	"github.com/ethereum/go-ethereum/common"
-	"github.com/ethereum/go-ethereum/crypto"
+	"github.com/ethereum/go-ethereum/crypto/sha3"
+	"github.com/ethereum/go-ethereum/logger"
+	"github.com/ethereum/go-ethereum/logger/glog"
+	"github.com/ethereum/go-ethereum/rlp"
 )
 
-func ParanoiaCheck(t1 *Trie, backend Backend) (bool, *Trie) {
-	t2 := New(nil, backend)
+const defaultCacheCapacity = 800
 
-	it := t1.Iterator()
-	for it.Next() {
-		t2.Update(it.Key, it.Value)
-	}
-
-	return bytes.Equal(t2.Hash(), t1.Hash()), t2
-}
-
-type Trie struct {
-	mu       sync.Mutex
-	root     Node
-	roothash []byte
-	cache    *Cache
-
-	revisions *list.List
-}
-
-func New(root []byte, backend Backend) *Trie {
-	trie := &Trie{}
-	trie.revisions = list.New()
-	trie.roothash = root
-	if backend != nil {
-		trie.cache = NewCache(backend)
-	}
+var (
+	// The global cache stores decoded trie nodes by hash as they get loaded.
+	globalCache = newARC(defaultCacheCapacity)
+	// This is the known root hash of an empty trie.
+	emptyRoot = common.HexToHash("56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421")
+)
 
-	if root != nil {
-		value := common.NewValueFromBytes(trie.cache.Get(root))
-		trie.root = trie.mknode(value)
-	}
+var ErrMissingRoot = errors.New("missing root node")
 
-	return trie
+// Database must be implemented by backing stores for the trie.
+type Database interface {
+	DatabaseWriter
+	// Get returns the value for key from the database.
+	Get(key []byte) (value []byte, err error)
 }
 
-func (self *Trie) Iterator() *Iterator {
-	return NewIterator(self)
+// DatabaseWriter wraps the Put method of a backing store for the trie.
+type DatabaseWriter interface {
+	// Put stores the mapping key->value in the database.
+	// Implementations must not hold onto the value bytes, the trie
+	// will reuse the slice across calls to Put.
+	Put(key, value []byte) error
 }
 
-func (self *Trie) Copy() *Trie {
-	cpy := make([]byte, 32)
-	copy(cpy, self.roothash) // NOTE: cpy isn't being used anywhere?
-	trie := New(nil, nil)
-	trie.cache = self.cache.Copy()
-	if self.root != nil {
-		trie.root = self.root.Copy(trie)
-	}
-
-	return trie
+// Trie is a Merkle Patricia Trie.
+// The zero value is an empty trie with no database.
+// Use New to create a trie that sits on top of a database.
+//
+// Trie is not safe for concurrent use.
+type Trie struct {
+	root node
+	db   Database
+	*hasher
 }
 
-// Legacy support
-func (self *Trie) Root() []byte { return self.Hash() }
-func (self *Trie) Hash() []byte {
-	var hash []byte
-	if self.root != nil {
-		t := self.root.Hash()
-		if byts, ok := t.([]byte); ok && len(byts) > 0 {
-			hash = byts
-		} else {
-			hash = crypto.Sha3(common.Encode(self.root.RlpData()))
+// New creates a trie with an existing root node from db.
+//
+// If root is the zero hash or the sha3 hash of an empty string, the
+// trie is initially empty and does not require a database. Otherwise,
+// New will panics if db is nil or root does not exist in the
+// database. Accessing the trie loads nodes from db on demand.
+func New(root common.Hash, db Database) (*Trie, error) {
+	trie := &Trie{db: db}
+	if (root != common.Hash{}) && root != emptyRoot {
+		if db == nil {
+			panic("trie.New: cannot use existing root without a database")
 		}
-	} else {
-		hash = crypto.Sha3(common.Encode(""))
-	}
-
-	if !bytes.Equal(hash, self.roothash) {
-		self.revisions.PushBack(self.roothash)
-		self.roothash = hash
+		if v, _ := trie.db.Get(root[:]); len(v) == 0 {
+			return nil, ErrMissingRoot
+		}
+		trie.root = hashNode(root.Bytes())
 	}
-
-	return hash
+	return trie, nil
 }
-func (self *Trie) Commit() {
-	self.mu.Lock()
-	defer self.mu.Unlock()
 
-	// Hash first
-	self.Hash()
-
-	self.cache.Flush()
+// Iterator returns an iterator over all mappings in the trie.
+func (t *Trie) Iterator() *Iterator {
+	return NewIterator(t)
 }
 
-// Reset should only be called if the trie has been hashed
-func (self *Trie) Reset() {
-	self.mu.Lock()
-	defer self.mu.Unlock()
-
-	self.cache.Reset()
-
-	if self.revisions.Len() > 0 {
-		revision := self.revisions.Remove(self.revisions.Back()).([]byte)
-		self.roothash = revision
+// Get returns the value for key stored in the trie.
+// The value bytes must not be modified by the caller.
+func (t *Trie) Get(key []byte) []byte {
+	key = compactHexDecode(key)
+	tn := t.root
+	for len(key) > 0 {
+		switch n := tn.(type) {
+		case shortNode:
+			if len(key) < len(n.Key) || !bytes.Equal(n.Key, key[:len(n.Key)]) {
+				return nil
+			}
+			tn = n.Val
+			key = key[len(n.Key):]
+		case fullNode:
+			tn = n[key[0]]
+			key = key[1:]
+		case nil:
+			return nil
+		case hashNode:
+			tn = t.resolveHash(n)
+		default:
+			panic(fmt.Sprintf("%T: invalid node: %v", tn, tn))
+		}
 	}
-	value := common.NewValueFromBytes(self.cache.Get(self.roothash))
-	self.root = self.mknode(value)
+	return tn.(valueNode)
 }
 
-func (self *Trie) UpdateString(key, value string) Node { return self.Update([]byte(key), []byte(value)) }
-func (self *Trie) Update(key, value []byte) Node {
-	self.mu.Lock()
-	defer self.mu.Unlock()
-
-	k := CompactHexDecode(key)
-
+// Update associates key with value in the trie. Subsequent calls to
+// Get will return value. If value has length zero, any existing value
+// is deleted from the trie and calls to Get will return nil.
+//
+// The value bytes must not be modified by the caller while they are
+// stored in the trie.
+func (t *Trie) Update(key, value []byte) {
+	k := compactHexDecode(key)
 	if len(value) != 0 {
-		node := NewValueNode(self, value)
-		node.dirty = true
-		self.root = self.insert(self.root, k, node)
+		t.root = t.insert(t.root, k, valueNode(value))
 	} else {
-		self.root = self.delete(self.root, k)
+		t.root = t.delete(t.root, k)
 	}
-
-	return self.root
-}
-
-func (self *Trie) GetString(key string) []byte { return self.Get([]byte(key)) }
-func (self *Trie) Get(key []byte) []byte {
-	self.mu.Lock()
-	defer self.mu.Unlock()
-
-	k := CompactHexDecode(key)
-
-	n := self.get(self.root, k)
-	if n != nil {
-		return n.(*ValueNode).Val()
-	}
-
-	return nil
 }
 
-func (self *Trie) DeleteString(key string) Node { return self.Delete([]byte(key)) }
-func (self *Trie) Delete(key []byte) Node {
-	self.mu.Lock()
-	defer self.mu.Unlock()
-
-	k := CompactHexDecode(key)
-	self.root = self.delete(self.root, k)
-
-	return self.root
-}
-
-func (self *Trie) insert(node Node, key []byte, value Node) Node {
+func (t *Trie) insert(n node, key []byte, value node) node {
 	if len(key) == 0 {
 		return value
 	}
-
-	if node == nil {
-		node := NewShortNode(self, key, value)
-		node.dirty = true
-		return node
-	}
-
-	switch node := node.(type) {
-	case *ShortNode:
-		k := node.Key()
-		cnode := node.Value()
-		if bytes.Equal(k, key) {
-			node := NewShortNode(self, key, value)
-			node.dirty = true
-			return node
-
+	switch n := n.(type) {
+	case shortNode:
+		matchlen := prefixLen(key, n.Key)
+		// If the whole key matches, keep this short node as is
+		// and only update the value.
+		if matchlen == len(n.Key) {
+			return shortNode{n.Key, t.insert(n.Val, key[matchlen:], value)}
 		}
-
-		var n Node
-		matchlength := MatchingNibbleLength(key, k)
-		if matchlength == len(k) {
-			n = self.insert(cnode, key[matchlength:], value)
-		} else {
-			pnode := self.insert(nil, k[matchlength+1:], cnode)
-			nnode := self.insert(nil, key[matchlength+1:], value)
-			fulln := NewFullNode(self)
-			fulln.dirty = true
-			fulln.set(k[matchlength], pnode)
-			fulln.set(key[matchlength], nnode)
-			n = fulln
-		}
-		if matchlength == 0 {
-			return n
+		// Otherwise branch out at the index where they differ.
+		var branch fullNode
+		branch[n.Key[matchlen]] = t.insert(nil, n.Key[matchlen+1:], n.Val)
+		branch[key[matchlen]] = t.insert(nil, key[matchlen+1:], value)
+		// Replace this shortNode with the branch if it occurs at index 0.
+		if matchlen == 0 {
+			return branch
 		}
+		// Otherwise, replace it with a short node leading up to the branch.
+		return shortNode{key[:matchlen], branch}
 
-		snode := NewShortNode(self, key[:matchlength], n)
-		snode.dirty = true
-		return snode
+	case fullNode:
+		n[key[0]] = t.insert(n[key[0]], key[1:], value)
+		return n
 
-	case *FullNode:
-		cpy := node.Copy(self).(*FullNode)
-		cpy.set(key[0], self.insert(node.branch(key[0]), key[1:], value))
-		cpy.dirty = true
+	case nil:
+		return shortNode{key, value}
 
-		return cpy
+	case hashNode:
+		// We've hit a part of the trie that isn't loaded yet. Load
+		// the node and insert into it. This leaves all child nodes on
+		// the path to the value in the trie.
+		//
+		// TODO: track whether insertion changed the value and keep
+		// n as a hash node if it didn't.
+		return t.insert(t.resolveHash(n), key, value)
 
 	default:
-		panic(fmt.Sprintf("%T: invalid node: %v", node, node))
+		panic(fmt.Sprintf("%T: invalid node: %v", n, n))
 	}
 }
 
-func (self *Trie) get(node Node, key []byte) Node {
-	if len(key) == 0 {
-		return node
-	}
-
-	if node == nil {
-		return nil
-	}
-
-	switch node := node.(type) {
-	case *ShortNode:
-		k := node.Key()
-		cnode := node.Value()
-
-		if len(key) >= len(k) && bytes.Equal(k, key[:len(k)]) {
-			return self.get(cnode, key[len(k):])
-		}
-
-		return nil
-	case *FullNode:
-		return self.get(node.branch(key[0]), key[1:])
-	default:
-		panic(fmt.Sprintf("%T: invalid node: %v", node, node))
-	}
+// Delete removes any existing value for key from the trie.
+func (t *Trie) Delete(key []byte) {
+	k := compactHexDecode(key)
+	t.root = t.delete(t.root, k)
 }
 
-func (self *Trie) delete(node Node, key []byte) Node {
-	if len(key) == 0 && node == nil {
-		return nil
-	}
-
-	switch node := node.(type) {
-	case *ShortNode:
-		k := node.Key()
-		cnode := node.Value()
-		if bytes.Equal(key, k) {
-			return nil
-		} else if bytes.Equal(key[:len(k)], k) {
-			child := self.delete(cnode, key[len(k):])
-
-			var n Node
-			switch child := child.(type) {
-			case *ShortNode:
-				nkey := append(k, child.Key()...)
-				n = NewShortNode(self, nkey, child.Value())
-				n.(*ShortNode).dirty = true
-			case *FullNode:
-				sn := NewShortNode(self, node.Key(), child)
-				sn.dirty = true
-				sn.key = node.key
-				n = sn
-			}
-
-			return n
-		} else {
-			return node
+// delete returns the new root of the trie with key deleted.
+// It reduces the trie to minimal form by simplifying
+// nodes on the way up after deleting recursively.
+func (t *Trie) delete(n node, key []byte) node {
+	switch n := n.(type) {
+	case shortNode:
+		matchlen := prefixLen(key, n.Key)
+		if matchlen < len(n.Key) {
+			return n // don't replace n on mismatch
+		}
+		if matchlen == len(key) {
+			return nil // remove n entirely for whole matches
+		}
+		// The key is longer than n.Key. Remove the remaining suffix
+		// from the subtrie. Child can never be nil here since the
+		// subtrie must contain at least two other values with keys
+		// longer than n.Key.
+		child := t.delete(n.Val, key[len(n.Key):])
+		switch child := child.(type) {
+		case shortNode:
+			// Deleting from the subtrie reduced it to another
+			// short node. Merge the nodes to avoid creating a
+			// shortNode{..., shortNode{...}}. Use concat (which
+			// always creates a new slice) instead of append to
+			// avoid modifying n.Key since it might be shared with
+			// other nodes.
+			return shortNode{concat(n.Key, child.Key...), child.Val}
+		default:
+			return shortNode{n.Key, child}
 		}
 
-	case *FullNode:
-		n := node.Copy(self).(*FullNode)
-		n.set(key[0], self.delete(n.branch(key[0]), key[1:]))
-		n.dirty = true
-
+	case fullNode:
+		n[key[0]] = t.delete(n[key[0]], key[1:])
+		// Check how many non-nil entries are left after deleting and
+		// reduce the full node to a short node if only one entry is
+		// left. Since n must've contained at least two children
+		// before deletion (otherwise it would not be a full node) n
+		// can never be reduced to nil.
+		//
+		// When the loop is done, pos contains the index of the single
+		// value that is left in n or -2 if n contains at least two
+		// values.
 		pos := -1
-		for i := 0; i < 17; i++ {
-			if n.branch(byte(i)) != nil {
+		for i, cld := range n {
+			if cld != nil {
 				if pos == -1 {
 					pos = i
 				} else {
 					pos = -2
+					break
 				}
 			}
 		}
-
-		var nnode Node
-		if pos == 16 {
-			nnode = NewShortNode(self, []byte{16}, n.branch(byte(pos)))
-			nnode.(*ShortNode).dirty = true
-		} else if pos >= 0 {
-			cnode := n.branch(byte(pos))
-			switch cnode := cnode.(type) {
-			case *ShortNode:
-				// Stitch keys
-				k := append([]byte{byte(pos)}, cnode.Key()...)
-				nnode = NewShortNode(self, k, cnode.Value())
-				nnode.(*ShortNode).dirty = true
-			case *FullNode:
-				nnode = NewShortNode(self, []byte{byte(pos)}, n.branch(byte(pos)))
-				nnode.(*ShortNode).dirty = true
+		if pos >= 0 {
+			if pos != 16 {
+				// If the remaining entry is a short node, it replaces
+				// n and its key gets the missing nibble tacked to the
+				// front. This avoids creating an invalid
+				// shortNode{..., shortNode{...}}.  Since the entry
+				// might not be loaded yet, resolve it just for this
+				// check.
+				cnode := t.resolve(n[pos])
+				if cnode, ok := cnode.(shortNode); ok {
+					k := append([]byte{byte(pos)}, cnode.Key...)
+					return shortNode{k, cnode.Val}
+				}
 			}
-		} else {
-			nnode = n
+			// Otherwise, n is replaced by a one-nibble short node
+			// containing the child.
+			return shortNode{[]byte{byte(pos)}, n[pos]}
 		}
+		// n still contains at least two values and cannot be reduced.
+		return n
 
-		return nnode
 	case nil:
 		return nil
+
+	case hashNode:
+		// We've hit a part of the trie that isn't loaded yet. Load
+		// the node and delete from it. This leaves all child nodes on
+		// the path to the value in the trie.
+		//
+		// TODO: track whether deletion actually hit a key and keep
+		// n as a hash node if it didn't.
+		return t.delete(t.resolveHash(n), key)
+
 	default:
-		panic(fmt.Sprintf("%T: invalid node: %v (%v)", node, node, key))
+		panic(fmt.Sprintf("%T: invalid node: %v (%v)", n, n, key))
 	}
 }
 
-// casting functions and cache storing
-func (self *Trie) mknode(value *common.Value) Node {
-	l := value.Len()
-	switch l {
-	case 0:
-		return nil
-	case 2:
-		// A value node may consists of 2 bytes.
-		if value.Get(0).Len() != 0 {
-			key := CompactDecode(value.Get(0).Bytes())
-			if key[len(key)-1] == 16 {
-				return NewShortNode(self, key, NewValueNode(self, value.Get(1).Bytes()))
-			} else {
-				return NewShortNode(self, key, self.mknode(value.Get(1)))
-			}
-		}
-	case 17:
-		if len(value.Bytes()) != 17 {
-			fnode := NewFullNode(self)
-			for i := 0; i < 16; i++ {
-				fnode.set(byte(i), self.mknode(value.Get(i)))
-			}
-			return fnode
+func concat(s1 []byte, s2 ...byte) []byte {
+	r := make([]byte, len(s1)+len(s2))
+	copy(r, s1)
+	copy(r[len(s1):], s2)
+	return r
+}
+
+func (t *Trie) resolve(n node) node {
+	if n, ok := n.(hashNode); ok {
+		return t.resolveHash(n)
+	}
+	return n
+}
+
+func (t *Trie) resolveHash(n hashNode) node {
+	if v, ok := globalCache.Get(n); ok {
+		return v
+	}
+	enc, err := t.db.Get(n)
+	if err != nil || enc == nil {
+		// TODO: This needs to be improved to properly distinguish errors.
+		// Disk I/O errors shouldn't produce nil (and cause a
+		// consensus failure or weird crash), but it is unclear how
+		// they could be handled because the entire stack above the trie isn't
+		// prepared to cope with missing state nodes.
+		if glog.V(logger.Error) {
+			glog.Errorf("Dangling hash node ref %x: %v", n, err)
 		}
-	case 32:
-		return NewHash(value.Bytes(), self)
+		return nil
+	}
+	dec := mustDecodeNode(n, enc)
+	if dec != nil {
+		globalCache.Put(n, dec)
 	}
+	return dec
+}
+
+// Root returns the root hash of the trie.
+// Deprecated: use Hash instead.
+func (t *Trie) Root() []byte { return t.Hash().Bytes() }
 
-	return NewValueNode(self, value.Bytes())
+// Hash returns the root hash of the trie. It does not write to the
+// database and can be used even if the trie doesn't have one.
+func (t *Trie) Hash() common.Hash {
+	root, _ := t.hashRoot(nil)
+	return common.BytesToHash(root.(hashNode))
 }
 
-func (self *Trie) trans(node Node) Node {
-	switch node := node.(type) {
-	case *HashNode:
-		value := common.NewValueFromBytes(self.cache.Get(node.key))
-		return self.mknode(value)
-	default:
-		return node
+// Commit writes all nodes to the trie's database.
+// Nodes are stored with their sha3 hash as the key.
+//
+// Committing flushes nodes from memory.
+// Subsequent Get calls will load nodes from the database.
+func (t *Trie) Commit() (root common.Hash, err error) {
+	if t.db == nil {
+		panic("Commit called on trie with nil database")
 	}
+	return t.CommitTo(t.db)
 }
 
-func (self *Trie) store(node Node) interface{} {
-	data := common.Encode(node)
-	if len(data) >= 32 {
-		key := crypto.Sha3(data)
-		if node.Dirty() {
-			//fmt.Println("save", node)
-			//fmt.Println()
-			self.cache.Put(key, data)
-		}
+// CommitTo writes all nodes to the given database.
+// Nodes are stored with their sha3 hash as the key.
+//
+// Committing flushes nodes from memory. Subsequent Get calls will
+// load nodes from the trie's database. Calling code must ensure that
+// the changes made to db are written back to the trie's attached
+// database before using the trie.
+func (t *Trie) CommitTo(db DatabaseWriter) (root common.Hash, err error) {
+	n, err := t.hashRoot(db)
+	if err != nil {
+		return (common.Hash{}), err
+	}
+	t.root = n
+	return common.BytesToHash(n.(hashNode)), nil
+}
 
-		return key
+func (t *Trie) hashRoot(db DatabaseWriter) (node, error) {
+	if t.root == nil {
+		return hashNode(emptyRoot.Bytes()), nil
+	}
+	if t.hasher == nil {
+		t.hasher = newHasher()
 	}
+	return t.hasher.hash(t.root, db, true)
+}
 
-	return node.RlpData()
+type hasher struct {
+	tmp *bytes.Buffer
+	sha hash.Hash
 }
 
-func (self *Trie) PrintRoot() {
-	fmt.Println(self.root)
-	fmt.Printf("root=%x\n", self.Root())
+func newHasher() *hasher {
+	return &hasher{tmp: new(bytes.Buffer), sha: sha3.NewKeccak256()}
+}
+
+func (h *hasher) hash(n node, db DatabaseWriter, force bool) (node, error) {
+	hashed, err := h.replaceChildren(n, db)
+	if err != nil {
+		return hashNode{}, err
+	}
+	if n, err = h.store(hashed, db, force); err != nil {
+		return hashNode{}, err
+	}
+	return n, nil
+}
+
+// hashChildren replaces child nodes of n with their hashes if the encoded
+// size of the child is larger than a hash.
+func (h *hasher) replaceChildren(n node, db DatabaseWriter) (node, error) {
+	var err error
+	switch n := n.(type) {
+	case shortNode:
+		n.Key = compactEncode(n.Key)
+		if _, ok := n.Val.(valueNode); !ok {
+			if n.Val, err = h.hash(n.Val, db, false); err != nil {
+				return n, err
+			}
+		}
+		if n.Val == nil {
+			// Ensure that nil children are encoded as empty strings.
+			n.Val = valueNode(nil)
+		}
+		return n, nil
+	case fullNode:
+		for i := 0; i < 16; i++ {
+			if n[i] != nil {
+				if n[i], err = h.hash(n[i], db, false); err != nil {
+					return n, err
+				}
+			} else {
+				// Ensure that nil children are encoded as empty strings.
+				n[i] = valueNode(nil)
+			}
+		}
+		if n[16] == nil {
+			n[16] = valueNode(nil)
+		}
+		return n, nil
+	default:
+		return n, nil
+	}
+}
+
+func (h *hasher) store(n node, db DatabaseWriter, force bool) (node, error) {
+	// Don't store hashes or empty nodes.
+	if _, isHash := n.(hashNode); n == nil || isHash {
+		return n, nil
+	}
+	h.tmp.Reset()
+	if err := rlp.Encode(h.tmp, n); err != nil {
+		panic("encode error: " + err.Error())
+	}
+	if h.tmp.Len() < 32 && !force {
+		// Nodes smaller than 32 bytes are stored inside their parent.
+		return n, nil
+	}
+	// Larger nodes are replaced by their hash and stored in the database.
+	h.sha.Reset()
+	h.sha.Write(h.tmp.Bytes())
+	key := hashNode(h.sha.Sum(nil))
+	if db != nil {
+		err := db.Put(key, h.tmp.Bytes())
+		return key, err
+	}
+	return key, nil
 }
diff --git a/trie/trie_test.go b/trie/trie_test.go
index ae4e5efe4..c96861bed 100644
--- a/trie/trie_test.go
+++ b/trie/trie_test.go
@@ -18,89 +18,109 @@ package trie
 
 import (
 	"bytes"
+	"encoding/binary"
 	"fmt"
+	"io/ioutil"
+	"os"
 	"testing"
 
+	"github.com/davecgh/go-spew/spew"
 	"github.com/ethereum/go-ethereum/common"
-	"github.com/ethereum/go-ethereum/crypto"
+	"github.com/ethereum/go-ethereum/ethdb"
 )
 
-type Db map[string][]byte
-
-func (self Db) Get(k []byte) ([]byte, error) { return self[string(k)], nil }
-func (self Db) Put(k, v []byte) error        { self[string(k)] = v; return nil }
-
-// Used for testing
-func NewEmpty() *Trie {
-	return New(nil, make(Db))
+func init() {
+	spew.Config.Indent = "    "
+	spew.Config.DisableMethods = true
 }
 
-func NewEmptySecure() *SecureTrie {
-	return NewSecure(nil, make(Db))
+// Used for testing
+func newEmpty() *Trie {
+	db, _ := ethdb.NewMemDatabase()
+	trie, _ := New(common.Hash{}, db)
+	return trie
 }
 
 func TestEmptyTrie(t *testing.T) {
-	trie := NewEmpty()
+	var trie Trie
 	res := trie.Hash()
-	exp := crypto.Sha3(common.Encode(""))
-	if !bytes.Equal(res, exp) {
+	exp := emptyRoot
+	if res != common.Hash(exp) {
 		t.Errorf("expected %x got %x", exp, res)
 	}
 }
 
 func TestNull(t *testing.T) {
-	trie := NewEmpty()
-
+	var trie Trie
 	key := make([]byte, 32)
 	value := common.FromHex("0x823140710bf13990e4500136726d8b55")
 	trie.Update(key, value)
 	value = trie.Get(key)
 }
 
+func TestMissingRoot(t *testing.T) {
+	db, _ := ethdb.NewMemDatabase()
+	trie, err := New(common.HexToHash("0beec7b5ea3f0fdbc95d0dd47f3c5bc275da8a33"), db)
+	if trie != nil {
+		t.Error("New returned non-nil trie for invalid root")
+	}
+	if err != ErrMissingRoot {
+		t.Error("New returned wrong error: %v", err)
+	}
+}
+
 func TestInsert(t *testing.T) {
-	trie := NewEmpty()
+	trie := newEmpty()
 
-	trie.UpdateString("doe", "reindeer")
-	trie.UpdateString("dog", "puppy")
-	trie.UpdateString("dogglesworth", "cat")
+	updateString(trie, "doe", "reindeer")
+	updateString(trie, "dog", "puppy")
+	updateString(trie, "dogglesworth", "cat")
 
-	exp := common.Hex2Bytes("8aad789dff2f538bca5d8ea56e8abe10f4c7ba3a5dea95fea4cd6e7c3a1168d3")
+	exp := common.HexToHash("8aad789dff2f538bca5d8ea56e8abe10f4c7ba3a5dea95fea4cd6e7c3a1168d3")
 	root := trie.Hash()
-	if !bytes.Equal(root, exp) {
+	if root != exp {
 		t.Errorf("exp %x got %x", exp, root)
 	}
 
-	trie = NewEmpty()
-	trie.UpdateString("A", "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa")
+	trie = newEmpty()
+	updateString(trie, "A", "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa")
 
-	exp = common.Hex2Bytes("d23786fb4a010da3ce639d66d5e904a11dbc02746d1ce25029e53290cabf28ab")
-	root = trie.Hash()
-	if !bytes.Equal(root, exp) {
+	exp = common.HexToHash("d23786fb4a010da3ce639d66d5e904a11dbc02746d1ce25029e53290cabf28ab")
+	root, err := trie.Commit()
+	if err != nil {
+		t.Fatalf("commit error: %v", err)
+	}
+	if root != exp {
 		t.Errorf("exp %x got %x", exp, root)
 	}
 }
 
 func TestGet(t *testing.T) {
-	trie := NewEmpty()
-
-	trie.UpdateString("doe", "reindeer")
-	trie.UpdateString("dog", "puppy")
-	trie.UpdateString("dogglesworth", "cat")
+	trie := newEmpty()
+	updateString(trie, "doe", "reindeer")
+	updateString(trie, "dog", "puppy")
+	updateString(trie, "dogglesworth", "cat")
+
+	for i := 0; i < 2; i++ {
+		res := getString(trie, "dog")
+		if !bytes.Equal(res, []byte("puppy")) {
+			t.Errorf("expected puppy got %x", res)
+		}
 
-	res := trie.GetString("dog")
-	if !bytes.Equal(res, []byte("puppy")) {
-		t.Errorf("expected puppy got %x", res)
-	}
+		unknown := getString(trie, "unknown")
+		if unknown != nil {
+			t.Errorf("expected nil got %x", unknown)
+		}
 
-	unknown := trie.GetString("unknown")
-	if unknown != nil {
-		t.Errorf("expected nil got %x", unknown)
+		if i == 1 {
+			return
+		}
+		trie.Commit()
 	}
 }
 
 func TestDelete(t *testing.T) {
-	trie := NewEmpty()
-
+	trie := newEmpty()
 	vals := []struct{ k, v string }{
 		{"do", "verb"},
 		{"ether", "wookiedoo"},
@@ -113,21 +133,21 @@ func TestDelete(t *testing.T) {
 	}
 	for _, val := range vals {
 		if val.v != "" {
-			trie.UpdateString(val.k, val.v)
+			updateString(trie, val.k, val.v)
 		} else {
-			trie.DeleteString(val.k)
+			deleteString(trie, val.k)
 		}
 	}
 
 	hash := trie.Hash()
-	exp := common.Hex2Bytes("5991bb8c6514148a29db676a14ac506cd2cd5775ace63c30a4fe457715e9ac84")
-	if !bytes.Equal(hash, exp) {
+	exp := common.HexToHash("5991bb8c6514148a29db676a14ac506cd2cd5775ace63c30a4fe457715e9ac84")
+	if hash != exp {
 		t.Errorf("expected %x got %x", exp, hash)
 	}
 }
 
 func TestEmptyValues(t *testing.T) {
-	trie := NewEmpty()
+	trie := newEmpty()
 
 	vals := []struct{ k, v string }{
 		{"do", "verb"},
@@ -140,78 +160,85 @@ func TestEmptyValues(t *testing.T) {
 		{"shaman", ""},
 	}
 	for _, val := range vals {
-		trie.UpdateString(val.k, val.v)
+		updateString(trie, val.k, val.v)
 	}
 
 	hash := trie.Hash()
-	exp := common.Hex2Bytes("5991bb8c6514148a29db676a14ac506cd2cd5775ace63c30a4fe457715e9ac84")
-	if !bytes.Equal(hash, exp) {
+	exp := common.HexToHash("5991bb8c6514148a29db676a14ac506cd2cd5775ace63c30a4fe457715e9ac84")
+	if hash != exp {
 		t.Errorf("expected %x got %x", exp, hash)
 	}
 }
 
 func TestReplication(t *testing.T) {
-	trie := NewEmpty()
+	trie := newEmpty()
 	vals := []struct{ k, v string }{
 		{"do", "verb"},
 		{"ether", "wookiedoo"},
 		{"horse", "stallion"},
 		{"shaman", "horse"},
 		{"doge", "coin"},
-		{"ether", ""},
 		{"dog", "puppy"},
-		{"shaman", ""},
 		{"somethingveryoddindeedthis is", "myothernodedata"},
 	}
 	for _, val := range vals {
-		trie.UpdateString(val.k, val.v)
+		updateString(trie, val.k, val.v)
 	}
-	trie.Commit()
-
-	trie2 := New(trie.Root(), trie.cache.backend)
-	if string(trie2.GetString("horse")) != "stallion" {
-		t.Error("expected to have horse => stallion")
+	exp, err := trie.Commit()
+	if err != nil {
+		t.Fatalf("commit error: %v", err)
 	}
 
-	hash := trie2.Hash()
-	exp := trie.Hash()
-	if !bytes.Equal(hash, exp) {
+	// create a new trie on top of the database and check that lookups work.
+	trie2, err := New(exp, trie.db)
+	if err != nil {
+		t.Fatalf("can't recreate trie at %x: %v", exp, err)
+	}
+	for _, kv := range vals {
+		if string(getString(trie2, kv.k)) != kv.v {
+			t.Errorf("trie2 doesn't have %q => %q", kv.k, kv.v)
+		}
+	}
+	hash, err := trie2.Commit()
+	if err != nil {
+		t.Fatalf("commit error: %v", err)
+	}
+	if hash != exp {
 		t.Errorf("root failure. expected %x got %x", exp, hash)
 	}
 
-}
-
-func TestReset(t *testing.T) {
-	trie := NewEmpty()
-	vals := []struct{ k, v string }{
+	// perform some insertions on the new trie.
+	vals2 := []struct{ k, v string }{
 		{"do", "verb"},
 		{"ether", "wookiedoo"},
 		{"horse", "stallion"},
+		// {"shaman", "horse"},
+		// {"doge", "coin"},
+		// {"ether", ""},
+		// {"dog", "puppy"},
+		// {"somethingveryoddindeedthis is", "myothernodedata"},
+		// {"shaman", ""},
 	}
-	for _, val := range vals {
-		trie.UpdateString(val.k, val.v)
+	for _, val := range vals2 {
+		updateString(trie2, val.k, val.v)
 	}
-	trie.Commit()
-
-	before := common.CopyBytes(trie.roothash)
-	trie.UpdateString("should", "revert")
-	trie.Hash()
-	// Should have no effect
-	trie.Hash()
-	trie.Hash()
-	// ###
-
-	trie.Reset()
-	after := common.CopyBytes(trie.roothash)
+	if trie2.Hash() != exp {
+		t.Errorf("root failure. expected %x got %x", exp, hash)
+	}
+}
 
-	if !bytes.Equal(before, after) {
-		t.Errorf("expected roots to be equal. %x - %x", before, after)
+func paranoiaCheck(t1 *Trie) (bool, *Trie) {
+	t2 := new(Trie)
+	it := NewIterator(t1)
+	for it.Next() {
+		t2.Update(it.Key, it.Value)
 	}
+	return t2.Hash() == t1.Hash(), t2
 }
 
 func TestParanoia(t *testing.T) {
 	t.Skip()
-	trie := NewEmpty()
+	trie := newEmpty()
 
 	vals := []struct{ k, v string }{
 		{"do", "verb"},
@@ -225,13 +252,13 @@ func TestParanoia(t *testing.T) {
 		{"somethingveryoddindeedthis is", "myothernodedata"},
 	}
 	for _, val := range vals {
-		trie.UpdateString(val.k, val.v)
+		updateString(trie, val.k, val.v)
 	}
 	trie.Commit()
 
-	ok, t2 := ParanoiaCheck(trie, trie.cache.backend)
+	ok, t2 := paranoiaCheck(trie)
 	if !ok {
-		t.Errorf("trie paranoia check failed %x %x", trie.roothash, t2.roothash)
+		t.Errorf("trie paranoia check failed %x %x", trie.Hash(), t2.Hash())
 	}
 }
 
@@ -240,51 +267,26 @@ func TestOutput(t *testing.T) {
 	t.Skip()
 
 	base := "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
-	trie := NewEmpty()
+	trie := newEmpty()
 	for i := 0; i < 50; i++ {
-		trie.UpdateString(fmt.Sprintf("%s%d", base, i), "valueeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee")
+		updateString(trie, fmt.Sprintf("%s%d", base, i), "valueeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee")
 	}
 	fmt.Println("############################## FULL ################################")
 	fmt.Println(trie.root)
 
 	trie.Commit()
 	fmt.Println("############################## SMALL ################################")
-	trie2 := New(trie.roothash, trie.cache.backend)
-	trie2.GetString(base + "20")
+	trie2, _ := New(trie.Hash(), trie.db)
+	getString(trie2, base+"20")
 	fmt.Println(trie2.root)
 }
 
-func BenchmarkGets(b *testing.B) {
-	trie := NewEmpty()
-	vals := []struct{ k, v string }{
-		{"do", "verb"},
-		{"ether", "wookiedoo"},
-		{"horse", "stallion"},
-		{"shaman", "horse"},
-		{"doge", "coin"},
-		{"ether", ""},
-		{"dog", "puppy"},
-		{"shaman", ""},
-		{"somethingveryoddindeedthis is", "myothernodedata"},
-	}
-	for _, val := range vals {
-		trie.UpdateString(val.k, val.v)
-	}
-
-	b.ResetTimer()
-	for i := 0; i < b.N; i++ {
-		trie.Get([]byte("horse"))
-	}
-}
-
-func BenchmarkUpdate(b *testing.B) {
-	trie := NewEmpty()
-
-	b.ResetTimer()
-	for i := 0; i < b.N; i++ {
-		trie.UpdateString(fmt.Sprintf("aaaaaaaaa%d", i), "value")
-	}
+func TestLargeValue(t *testing.T) {
+	trie := newEmpty()
+	trie.Update([]byte("key1"), []byte{99, 99, 99, 99})
+	trie.Update([]byte("key2"), bytes.Repeat([]byte{1}, 32))
 	trie.Hash()
+
 }
 
 type kv struct {
@@ -293,7 +295,7 @@ type kv struct {
 }
 
 func TestLargeData(t *testing.T) {
-	trie := NewEmpty()
+	trie := newEmpty()
 	vals := make(map[string]*kv)
 
 	for i := byte(0); i < 255; i++ {
@@ -305,7 +307,7 @@ func TestLargeData(t *testing.T) {
 		vals[string(value2.k)] = value2
 	}
 
-	it := trie.Iterator()
+	it := NewIterator(trie)
 	for it.Next() {
 		vals[string(it.Key)].t = true
 	}
@@ -325,30 +327,82 @@ func TestLargeData(t *testing.T) {
 	}
 }
 
-func TestSecureDelete(t *testing.T) {
-	trie := NewEmptySecure()
+func BenchmarkGet(b *testing.B)      { benchGet(b, false) }
+func BenchmarkGetDB(b *testing.B)    { benchGet(b, true) }
+func BenchmarkUpdateBE(b *testing.B) { benchUpdate(b, binary.BigEndian) }
+func BenchmarkUpdateLE(b *testing.B) { benchUpdate(b, binary.LittleEndian) }
+func BenchmarkHashBE(b *testing.B)   { benchHash(b, binary.BigEndian) }
+func BenchmarkHashLE(b *testing.B)   { benchHash(b, binary.LittleEndian) }
 
-	vals := []struct{ k, v string }{
-		{"do", "verb"},
-		{"ether", "wookiedoo"},
-		{"horse", "stallion"},
-		{"shaman", "horse"},
-		{"doge", "coin"},
-		{"ether", ""},
-		{"dog", "puppy"},
-		{"shaman", ""},
+const benchElemCount = 20000
+
+func benchGet(b *testing.B, commit bool) {
+	trie := new(Trie)
+	if commit {
+		dir, tmpdb := tempDB()
+		defer os.RemoveAll(dir)
+		trie, _ = New(common.Hash{}, tmpdb)
 	}
-	for _, val := range vals {
-		if val.v != "" {
-			trie.UpdateString(val.k, val.v)
-		} else {
-			trie.DeleteString(val.k)
-		}
+	k := make([]byte, 32)
+	for i := 0; i < benchElemCount; i++ {
+		binary.LittleEndian.PutUint64(k, uint64(i))
+		trie.Update(k, k)
+	}
+	binary.LittleEndian.PutUint64(k, benchElemCount/2)
+	if commit {
+		trie.Commit()
 	}
 
-	hash := trie.Hash()
-	exp := common.Hex2Bytes("29b235a58c3c25ab83010c327d5932bcf05324b7d6b1185e650798034783ca9d")
-	if !bytes.Equal(hash, exp) {
-		t.Errorf("expected %x got %x", exp, hash)
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		trie.Get(k)
 	}
 }
+
+func benchUpdate(b *testing.B, e binary.ByteOrder) *Trie {
+	trie := newEmpty()
+	k := make([]byte, 32)
+	for i := 0; i < b.N; i++ {
+		e.PutUint64(k, uint64(i))
+		trie.Update(k, k)
+	}
+	return trie
+}
+
+func benchHash(b *testing.B, e binary.ByteOrder) {
+	trie := newEmpty()
+	k := make([]byte, 32)
+	for i := 0; i < benchElemCount; i++ {
+		e.PutUint64(k, uint64(i))
+		trie.Update(k, k)
+	}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		trie.Hash()
+	}
+}
+
+func tempDB() (string, Database) {
+	dir, err := ioutil.TempDir("", "trie-bench")
+	if err != nil {
+		panic(fmt.Sprintf("can't create temporary directory: %v", err))
+	}
+	db, err := ethdb.NewLDBDatabase(dir, 300*1024)
+	if err != nil {
+		panic(fmt.Sprintf("can't create temporary database: %v", err))
+	}
+	return dir, db
+}
+
+func getString(trie *Trie, k string) []byte {
+	return trie.Get([]byte(k))
+}
+
+func updateString(trie *Trie, k, v string) {
+	trie.Update([]byte(k), []byte(v))
+}
+
+func deleteString(trie *Trie, k string) {
+	trie.Delete([]byte(k))
+}
diff --git a/trie/valuenode.go b/trie/valuenode.go
deleted file mode 100644
index 0afa64d54..000000000
--- a/trie/valuenode.go
+++ /dev/null
@@ -1,42 +0,0 @@
-// Copyright 2014 The go-ethereum Authors
-// This file is part of the go-ethereum library.
-//
-// The go-ethereum library is free software: you can redistribute it and/or modify
-// it under the terms of the GNU Lesser General Public License as published by
-// the Free Software Foundation, either version 3 of the License, or
-// (at your option) any later version.
-//
-// The go-ethereum library is distributed in the hope that it will be useful,
-// but WITHOUT ANY WARRANTY; without even the implied warranty of
-// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
-// GNU Lesser General Public License for more details.
-//
-// You should have received a copy of the GNU Lesser General Public License
-// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
-
-package trie
-
-import "github.com/ethereum/go-ethereum/common"
-
-type ValueNode struct {
-	trie  *Trie
-	data  []byte
-	dirty bool
-}
-
-func NewValueNode(trie *Trie, data []byte) *ValueNode {
-	return &ValueNode{trie, data, false}
-}
-
-func (self *ValueNode) Value() Node { return self } // Best not to call :-)
-func (self *ValueNode) Val() []byte { return self.data }
-func (self *ValueNode) Dirty() bool { return self.dirty }
-func (self *ValueNode) Copy(t *Trie) Node {
-	return &ValueNode{t, common.CopyBytes(self.data), self.dirty}
-}
-func (self *ValueNode) RlpData() interface{} { return self.data }
-func (self *ValueNode) Hash() interface{}    { return self.data }
-
-func (self *ValueNode) setDirty(dirty bool) {
-	self.dirty = dirty
-}