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