6736ef96ea
The next revision, 19185, renames several runtime files, and will be handled in a separate change. From-SVN: r211328
70 lines
1.7 KiB
Go
70 lines
1.7 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 "strconv"
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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]uint32
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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) Error() 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, 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] = uint32(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 += uint8(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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// 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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// xorKeyStreamGeneric sets dst to the result of XORing src with the
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// key stream. Dst and src may be the same slice but otherwise should
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// not overlap.
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//
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// This is the pure Go version. rc4_{amd64,386,arm}* contain assembly
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// implementations. This is here for tests and to prevent bitrot.
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func (c *Cipher) xorKeyStreamGeneric(dst, src []byte) {
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i, j := c.i, c.j
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for k, v := range src {
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i += 1
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j += uint8(c.s[i])
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c.s[i], c.s[j] = c.s[j], c.s[i]
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dst[k] = v ^ uint8(c.s[uint8(c.s[i]+c.s[j])])
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}
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c.i, c.j = i, j
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}
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