libgo/go/crypto/rc4/rc4.go

   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 }