81 lines
1.9 KiB
Go
81 lines
1.9 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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//
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// RC4 is cryptographically broken and should not be used for secure
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// applications.
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package rc4
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import (
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"crypto/internal/subtle"
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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]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 and makes the Cipher unusable.
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//
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// Deprecated: Reset can't guarantee that the key will be entirely removed from
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// the 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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// XORKeyStream sets dst to the result of XORing src with the key stream.
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// Dst and src must overlap entirely or not at all.
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func (c *Cipher) XORKeyStream(dst, src []byte) {
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if len(src) == 0 {
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return
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}
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if subtle.InexactOverlap(dst[:len(src)], src) {
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panic("crypto/rc4: invalid buffer overlap")
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}
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i, j := c.i, c.j
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_ = dst[len(src)-1]
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dst = dst[:len(src)] // eliminate bounds check from loop
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for k, v := range src {
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i += 1
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x := c.s[i]
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j += uint8(x)
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y := c.s[j]
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c.s[i], c.s[j] = y, x
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dst[k] = v ^ uint8(c.s[uint8(x+y)])
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}
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c.i, c.j = i, j
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}
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