path: root/p2p/enr/enr.go

// Copyright 2017 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 enr implements Ethereum Node Records as defined in EIP-778. A node record holds
// arbitrary information about a node on the peer-to-peer network.
//
// Records contain named keys. To store and retrieve key/values in a record, use the Entry
// interface.
//
// Records must be signed before transmitting them to another node. Decoding a record verifies
// its signature. When creating a record, set the entries you want, then call Sign to add the
// signature. Modifying a record invalidates the signature.
//
// Package enr supports the "secp256k1-keccak" identity scheme.
package enr

import (
    "bytes"
    "crypto/ecdsa"
    "errors"
    "fmt"
    "io"
    "sort"

    "github.com/ethereum/go-ethereum/crypto"
    "github.com/ethereum/go-ethereum/crypto/sha3"
    "github.com/ethereum/go-ethereum/rlp"
)

const SizeLimit = 300 // maximum encoded size of a node record in bytes

const ID_SECP256k1_KECCAK = ID("secp256k1-keccak") // the default identity scheme

var (
    errNoID           = errors.New("unknown or unspecified identity scheme")
    errInvalidSigsize = errors.New("invalid signature size")
    errInvalidSig     = errors.New("invalid signature")
    errNotSorted      = errors.New("record key/value pairs are not sorted by key")
    errDuplicateKey   = errors.New("record contains duplicate key")
    errIncompletePair = errors.New("record contains incomplete k/v pair")
    errTooBig         = fmt.Errorf("record bigger than %d bytes", SizeLimit)
    errEncodeUnsigned = errors.New("can't encode unsigned record")
    errNotFound       = errors.New("no such key in record")
)

// Record represents a node record. The zero value is an empty record.
type Record struct {
    seq       uint64 // sequence number
    signature []byte // the signature
    raw       []byte // RLP encoded record
    pairs     []pair // sorted list of all key/value pairs
}

// pair is a key/value pair in a record.
type pair struct {
    k string
    v rlp.RawValue
}

// Signed reports whether the record has a valid signature.
func (r *Record) Signed() bool {
    return r.signature != nil
}

// Seq returns the sequence number.
func (r *Record) Seq() uint64 {
    return r.seq
}

// SetSeq updates the record sequence number. This invalidates any signature on the record.
// Calling SetSeq is usually not required because signing the redord increments the
// sequence number.
func (r *Record) SetSeq(s uint64) {
    r.signature = nil
    r.raw = nil
    r.seq = s
}

// Load retrieves the value of a key/value pair. The given Entry must be a pointer and will
// be set to the value of the entry in the record.
//
// Errors returned by Load are wrapped in KeyError. You can distinguish decoding errors
// from missing keys using the IsNotFound function.
func (r *Record) Load(e Entry) error {
    i := sort.Search(len(r.pairs), func(i int) bool { return r.pairs[i].k >= e.ENRKey() })
    if i < len(r.pairs) && r.pairs[i].k == e.ENRKey() {
        if err := rlp.DecodeBytes(r.pairs[i].v, e); err != nil {
            return &KeyError{Key: e.ENRKey(), Err: err}
        }
        return nil
    }
    return &KeyError{Key: e.ENRKey(), Err: errNotFound}
}

// Set adds or updates the given entry in the record.
// It panics if the value can't be encoded.
func (r *Record) Set(e Entry) {
    r.signature = nil
    r.raw = nil
    blob, err := rlp.EncodeToBytes(e)
    if err != nil {
        panic(fmt.Errorf("enr: can't encode %s: %v", e.ENRKey(), err))
    }

    i := sort.Search(len(r.pairs), func(i int) bool { return r.pairs[i].k >= e.ENRKey() })

    if i < len(r.pairs) && r.pairs[i].k == e.ENRKey() {
        // element is present at r.pairs[i]
        r.pairs[i].v = blob
        return
    } else if i < len(r.pairs) {
        // insert pair before i-th elem
        el := pair{e.ENRKey(), blob}
        r.pairs = append(r.pairs, pair{})
        copy(r.pairs[i+1:], r.pairs[i:])
        r.pairs[i] = el
        return
    }

    // element should be placed at the end of r.pairs
    r.pairs = append(r.pairs, pair{e.ENRKey(), blob})
}

// EncodeRLP implements rlp.Encoder. Encoding fails if
// the record is unsigned.
func (r Record) EncodeRLP(w io.Writer) error {
    if !r.Signed() {
        return errEncodeUnsigned
    }
    _, err := w.Write(r.raw)
    return err
}

// DecodeRLP implements rlp.Decoder. Decoding verifies the signature.
func (r *Record) DecodeRLP(s *rlp.Stream) error {
    raw, err := s.Raw()
    if err != nil {
        return err
    }
    if len(raw) > SizeLimit {
        return errTooBig
    }

    // Decode the RLP container.
    dec := Record{raw: raw}
    s = rlp.NewStream(bytes.NewReader(raw), 0)
    if _, err := s.List(); err != nil {
        return err
    }
    if err = s.Decode(&dec.signature); err != nil {
        return err
    }
    if err = s.Decode(&dec.seq); err != nil {
        return err
    }
    // The rest of the record contains sorted k/v pairs.
    var prevkey string
    for i := 0; ; i++ {
        var kv pair
        if err := s.Decode(&kv.k); err != nil {
            if err == rlp.EOL {
                break
            }
            return err
        }
        if err := s.Decode(&kv.v); err != nil {
            if err == rlp.EOL {
                return errIncompletePair
            }
            return err
        }
        if i > 0 {
            if kv.k == prevkey {
                return errDuplicateKey
            }
            if kv.k < prevkey {
                return errNotSorted
            }
        }
        dec.pairs = append(dec.pairs, kv)
        prevkey = kv.k
    }
    if err := s.ListEnd(); err != nil {
        return err
    }

    // Verify signature.
    if err = dec.verifySignature(); err != nil {
        return err
    }
    *r = dec
    return nil
}

type s256raw []byte

func (s256raw) ENRKey() string { return "secp256k1" }

// NodeAddr returns the node address. The return value will be nil if the record is
// unsigned.
func (r *Record) NodeAddr() []byte {
    var entry s256raw
    if r.Load(&entry) != nil {
        return nil
    }
    return crypto.Keccak256(entry)
}

// Sign signs the record with the given private key. It updates the record's identity
// scheme, public key and increments the sequence number. Sign returns an error if the
// encoded record is larger than the size limit.
func (r *Record) Sign(privkey *ecdsa.PrivateKey) error {
    r.seq = r.seq + 1
    r.Set(ID_SECP256k1_KECCAK)
    r.Set(Secp256k1(privkey.PublicKey))
    return r.signAndEncode(privkey)
}

func (r *Record) appendPairs(list []interface{}) []interface{} {
    list = append(list, r.seq)
    for _, p := range r.pairs {
        list = append(list, p.k, p.v)
    }
    return list
}

func (r *Record) signAndEncode(privkey *ecdsa.PrivateKey) error {
    // Put record elements into a flat list. Leave room for the signature.
    list := make([]interface{}, 1, len(r.pairs)*2+2)
    list = r.appendPairs(list)

    // Sign the tail of the list.
    h := sha3.NewKeccak256()
    rlp.Encode(h, list[1:])
    sig, err := crypto.Sign(h.Sum(nil), privkey)
    if err != nil {
        return err
    }
    sig = sig[:len(sig)-1] // remove v

    // Put signature in front.
    r.signature, list[0] = sig, sig
    r.raw, err = rlp.EncodeToBytes(list)
    if err != nil {
        return err
    }
    if len(r.raw) > SizeLimit {
        return errTooBig
    }
    return nil
}

func (r *Record) verifySignature() error {
    // Get identity scheme, public key, signature.
    var id ID
    var entry s256raw
    if err := r.Load(&id); err != nil {
        return err
    } else if id != ID_SECP256k1_KECCAK {
        return errNoID
    }
    if err := r.Load(&entry); err != nil {
        return err
    } else if len(entry) != 33 {
        return fmt.Errorf("invalid public key")
    }

    // Verify the signature.
    list := make([]interface{}, 0, len(r.pairs)*2+1)
    list = r.appendPairs(list)
    h := sha3.NewKeccak256()
    rlp.Encode(h, list)
    if !crypto.VerifySignature(entry, h.Sum(nil), r.signature) {
        return errInvalidSig
    }
    return nil
}