67 lines
1.6 KiB
Go
67 lines
1.6 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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// Package rc4 implements RC4 encryption, as defined in Bruce Schneier's
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// Applied Cryptography.
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package rc4
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// BUG(agl): RC4 is in common use but has design weaknesses that make
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// it a poor choice for new protocols.
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import (
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"os"
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"strconv"
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)
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// A Cipher is an instance of RC4 using a particular key.
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type Cipher struct {
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s [256]byte
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i, j uint8
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}
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type KeySizeError int
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func (k KeySizeError) String() string {
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return "crypto/rc4: invalid key size " + strconv.Itoa(int(k))
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}
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// NewCipher creates and returns a new Cipher. The key argument should be the
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// RC4 key, at least 1 byte and at most 256 bytes.
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func NewCipher(key []byte) (*Cipher, os.Error) {
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k := len(key)
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if k < 1 || k > 256 {
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return nil, KeySizeError(k)
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}
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var c Cipher
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for i := 0; i < 256; i++ {
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c.s[i] = uint8(i)
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}
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var j uint8 = 0
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for i := 0; i < 256; i++ {
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j += c.s[i] + key[i%k]
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c.s[i], c.s[j] = c.s[j], c.s[i]
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}
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return &c, nil
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}
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// XORKeyStream sets dst to the result of XORing src with the key stream.
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// Dst and src may be the same slice but otherwise should not overlap.
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func (c *Cipher) XORKeyStream(dst, src []byte) {
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for i := range src {
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c.i += 1
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c.j += c.s[c.i]
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c.s[c.i], c.s[c.j] = c.s[c.j], c.s[c.i]
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dst[i] = src[i] ^ c.s[c.s[c.i]+c.s[c.j]]
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}
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}
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// Reset zeros the key data so that it will no longer appear in the
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// process's memory.
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func (c *Cipher) Reset() {
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for i := range c.s {
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c.s[i] = 0
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}
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c.i, c.j = 0, 0
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}
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