67 lines
1.8 KiB
Go
67 lines
1.8 KiB
Go
|
// Copyright 2009 The Go Authors. All rights reserved.
|
||
|
|
// Use of this source code is governed by a BSD-style
|
||
|
|
// license that can be found in the LICENSE file.
|
||
|
|
|
||
|
|
/*
|
||
|
|
Implementation adapted from Needham and Wheeler's paper:
|
||
|
|
http://www.cix.co.uk/~klockstone/xtea.pdf
|
||
|
|
|
||
|
|
A precalculated look up table is used during encryption/decryption for values that are based purely on the key.
|
||
|
|
*/
|
||
|
|
|
||
|
|
package xtea
|
||
|
|
|
||
|
|
// XTEA is based on 64 rounds.
|
||
|
|
const numRounds = 64
|
||
|
|
|
||
|
|
// blockToUint32 reads an 8 byte slice into two uint32s.
|
||
|
|
// The block is treated as big endian.
|
||
|
|
func blockToUint32(src []byte) (uint32, uint32) {
|
||
|
|
r0 := uint32(src[0])<<24 | uint32(src[1])<<16 | uint32(src[2])<<8 | uint32(src[3])
|
||
|
|
r1 := uint32(src[4])<<24 | uint32(src[5])<<16 | uint32(src[6])<<8 | uint32(src[7])
|
||
|
|
return r0, r1
|
||
|
|
}
|
||
|
|
|
||
|
|
// uint32ToBlock writes two uint32s into an 8 byte data block.
|
||
|
|
// Values are written as big endian.
|
||
|
|
func uint32ToBlock(v0, v1 uint32, dst []byte) {
|
||
|
|
dst[0] = byte(v0 >> 24)
|
||
|
|
dst[1] = byte(v0 >> 16)
|
||
|
|
dst[2] = byte(v0 >> 8)
|
||
|
|
dst[3] = byte(v0)
|
||
|
|
dst[4] = byte(v1 >> 24)
|
||
|
|
dst[5] = byte(v1 >> 16)
|
||
|
|
dst[6] = byte(v1 >> 8)
|
||
|
|
dst[7] = byte(v1 >> 0)
|
||
|
|
}
|
||
|
|
|
||
|
|
// encryptBlock encrypts a single 8 byte block using XTEA.
|
||
|
|
func encryptBlock(c *Cipher, dst, src []byte) {
|
||
|
|
v0, v1 := blockToUint32(src)
|
||
|
|
|
||
|
|
// Two rounds of XTEA applied per loop
|
||
|
|
for i := 0; i < numRounds; {
|
||
|
|
v0 += ((v1<<4 ^ v1>>5) + v1) ^ c.table[i]
|
||
|
|
i++
|
||
|
|
v1 += ((v0<<4 ^ v0>>5) + v0) ^ c.table[i]
|
||
|
|
i++
|
||
|
|
}
|
||
|
|
|
||
|
|
uint32ToBlock(v0, v1, dst)
|
||
|
|
}
|
||
|
|
|
||
|
|
// decryptBlock decrypt a single 8 byte block using XTEA.
|
||
|
|
func decryptBlock(c *Cipher, dst, src []byte) {
|
||
|
|
v0, v1 := blockToUint32(src)
|
||
|
|
|
||
|
|
// Two rounds of XTEA applied per loop
|
||
|
|
for i := numRounds; i > 0; {
|
||
|
|
i--
|
||
|
|
v1 -= ((v0<<4 ^ v0>>5) + v0) ^ c.table[i]
|
||
|
|
i--
|
||
|
|
v0 -= ((v1<<4 ^ v1>>5) + v1) ^ c.table[i]
|
||
|
|
}
|
||
|
|
|
||
|
|
uint32ToBlock(v0, v1, dst)
|
||
|
|
}
|