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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"
)
const KeyLength = 32
type Key []byte
type Encryption interface {
Encrypt(data []byte, key Key) ([]byte, error)
Decrypt(data []byte, key Key) ([]byte, error)
}
type encryption struct {
padding int
initCtr uint32
hashFunc func() hash.Hash
}
func New(padding int, initCtr uint32, hashFunc func() hash.Hash) *encryption {
return &encryption{
padding: padding,
initCtr: initCtr,
hashFunc: hashFunc,
}
}
func (e *encryption) Encrypt(data []byte, key Key) ([]byte, error) {
length := len(data)
isFixedPadding := e.padding > 0
if isFixedPadding && length > e.padding {
return nil, fmt.Errorf("Data length longer than padding, data length %v padding %v", length, e.padding)
}
paddedData := data
if isFixedPadding && length < e.padding {
paddedData = make([]byte, e.padding)
copy(paddedData[:length], data)
rand.Read(paddedData[length:])
}
return e.transform(paddedData, key), nil
}
func (e *encryption) Decrypt(data []byte, key Key) ([]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)
}
return e.transform(data, key), nil
}
func (e *encryption) transform(data []byte, key Key) []byte {
dataLength := len(data)
transformedData := make([]byte, dataLength)
hasher := e.hashFunc()
ctr := e.initCtr
hashSize := hasher.Size()
for i := 0; i < dataLength; i += hashSize {
hasher.Write(key)
ctrBytes := make([]byte, 4)
binary.LittleEndian.PutUint32(ctrBytes, ctr)
hasher.Write(ctrBytes)
ctrHash := hasher.Sum(nil)
hasher.Reset()
hasher.Write(ctrHash)
segmentKey := hasher.Sum(nil)
hasher.Reset()
segmentSize := min(hashSize, dataLength-i)
for j := 0; j < segmentSize; j++ {
transformedData[i+j] = data[i+j] ^ segmentKey[j]
}
ctr++
}
return transformedData
}
func GenerateRandomKey() (Key, error) {
key := make([]byte, KeyLength)
_, err := rand.Read(key)
return key, err
}
func min(x, y int) int {
if x < y {
return x
}
return y
}
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