1 // Copyright 2009 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 // Package rc4 implements RC4 encryption, as defined in Bruce Schneier's 6 // Applied Cryptography. 7 package rc4 8 9 // BUG(agl): RC4 is in common use but has design weaknesses that make 10 // it a poor choice for new protocols. 11 12 import "strconv" 13 14 // A Cipher is an instance of RC4 using a particular key. 15 type Cipher struct { 16 s [256]uint32 17 i, j uint8 18 } 19 20 type KeySizeError int 21 22 func (k KeySizeError) Error() string { 23 return "crypto/rc4: invalid key size " + strconv.Itoa(int(k)) 24 } 25 26 // NewCipher creates and returns a new Cipher. The key argument should be the 27 // RC4 key, at least 1 byte and at most 256 bytes. 28 func NewCipher(key []byte) (*Cipher, error) { 29 k := len(key) 30 if k < 1 || k > 256 { 31 return nil, KeySizeError(k) 32 } 33 var c Cipher 34 for i := 0; i < 256; i++ { 35 c.s[i] = uint32(i) 36 } 37 var j uint8 = 0 38 for i := 0; i < 256; i++ { 39 j += uint8(c.s[i]) + key[i%k] 40 c.s[i], c.s[j] = c.s[j], c.s[i] 41 } 42 return &c, nil 43 } 44 45 // Reset zeros the key data so that it will no longer appear in the 46 // process's memory. 47 func (c *Cipher) Reset() { 48 for i := range c.s { 49 c.s[i] = 0 50 } 51 c.i, c.j = 0, 0 52 } 53 54 // xorKeyStreamGeneric sets dst to the result of XORing src with the 55 // key stream. Dst and src may be the same slice but otherwise should 56 // not overlap. 57 // 58 // This is the pure Go version. rc4_{amd64,386,arm}* contain assembly 59 // implementations. This is here for tests and to prevent bitrot. 60 func (c *Cipher) xorKeyStreamGeneric(dst, src []byte) { 61 i, j := c.i, c.j 62 for k, v := range src { 63 i += 1 64 j += uint8(c.s[i]) 65 c.s[i], c.s[j] = c.s[j], c.s[i] 66 dst[k] = v ^ uint8(c.s[uint8(c.s[i]+c.s[j])]) 67 } 68 c.i, c.j = i, j 69 } 70
