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// Copyright 2018 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 encryption
import (
"crypto/rand"
"encoding/binary"
"fmt"
"hash"
"sync"
)
const KeyLength = 32
type Key []byte
type Encryption interface {
Encrypt(data []byte) ([]byte, error)
Decrypt(data []byte) ([]byte, error)
}
type encryption struct {
key Key // the encryption key (hashSize bytes long)
keyLen int // length of the key = length of blockcipher block
padding int // encryption will pad the data upto this if > 0
initCtr uint32 // initial counter used for counter mode blockcipher
hashFunc func() hash.Hash // hasher constructor function
}
// New constructs a new encryptor/decryptor
func New(key Key, padding int, initCtr uint32, hashFunc func() hash.Hash) *encryption {
return &encryption{
key: key,
keyLen: len(key),
padding: padding,
initCtr: initCtr,
hashFunc: hashFunc,
}
}
// Encrypt encrypts the data and does padding if specified
func (e *encryption) Encrypt(data []byte) ([]byte, error) {
length := len(data)
outLength := length
isFixedPadding := e.padding > 0
if isFixedPadding {
if length > e.padding {
return nil, fmt.Errorf("Data length longer than padding, data length %v padding %v", length, e.padding)
}
outLength = e.padding
}
out := make([]byte, outLength)
e.transform(data, out)
return out, nil
}
// Decrypt decrypts the data, if padding was used caller must know original length and truncate
func (e *encryption) Decrypt(data []byte) ([]byte, error) {
length := len(data)
if e.padding > 0 && length != e.padding {
return nil, fmt.Errorf("Data length different than padding, data length %v padding %v", length, e.padding)
}
out := make([]byte, length)
e.transform(data, out)
return out, nil
}
//
func (e *encryption) transform(in, out []byte) {
inLength := len(in)
wg := sync.WaitGroup{}
wg.Add((inLength-1)/e.keyLen + 1)
for i := 0; i < inLength; i += e.keyLen {
l := min(e.keyLen, inLength-i)
// call transformations per segment (asyncronously)
go func(i int, x, y []byte) {
defer wg.Done()
e.Transcrypt(i, x, y)
}(i/e.keyLen, in[i:i+l], out[i:i+l])
}
// pad the rest if out is longer
pad(out[inLength:])
wg.Wait()
}
// used for segmentwise transformation
// if in is shorter than out, padding is used
func (e *encryption) Transcrypt(i int, in []byte, out []byte) {
// first hash key with counter (initial counter + i)
hasher := e.hashFunc()
hasher.Write(e.key)
ctrBytes := make([]byte, 4)
binary.LittleEndian.PutUint32(ctrBytes, uint32(i)+e.initCtr)
hasher.Write(ctrBytes)
ctrHash := hasher.Sum(nil)
hasher.Reset()
// second round of hashing for selective disclosure
hasher.Write(ctrHash)
segmentKey := hasher.Sum(nil)
hasher.Reset()
// XOR bytes uptil length of in (out must be at least as long)
inLength := len(in)
for j := 0; j < inLength; j++ {
out[j] = in[j] ^ segmentKey[j]
}
// insert padding if out is longer
pad(out[inLength:])
}
func pad(b []byte) {
l := len(b)
for total := 0; total < l; {
read, _ := rand.Read(b[total:])
total += read
}
}
// GenerateRandomKey generates a random key of length l
func GenerateRandomKey(l int) Key {
key := make([]byte, l)
var total int
for total < l {
read, _ := rand.Read(key[total:])
total += read
}
return key
}
func min(x, y int) int {
if x < y {
return x
}
return y
}
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