libgo/go/crypto/aes/cipher.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 aes
   6
   7 import (
   8         "os"
   9         "strconv"
  10 )
  11
  12 // The AES block size in bytes.
  13 const BlockSize = 16
  14
  15 // A Cipher is an instance of AES encryption using a particular key.
  16 type Cipher struct {
  17         enc []uint32
  18         dec []uint32
  19 }
  20
  21 type KeySizeError int
  22
  23 func (k KeySizeError) String() string {
  24         return "crypto/aes: invalid key size " + strconv.Itoa(int(k))
  25 }
  26
  27 // NewCipher creates and returns a new Cipher.
  28 // The key argument should be the AES key,
  29 // either 16, 24, or 32 bytes to select
  30 // AES-128, AES-192, or AES-256.
  31 func NewCipher(key []byte) (*Cipher, os.Error) {
  32         k := len(key)
  33         switch k {
  34         default:
  35                 return nil, KeySizeError(k)
  36         case 16, 24, 32:
  37                 break
  38         }
  39
  40         n := k + 28
  41         c := &Cipher{make([]uint32, n), make([]uint32, n)}
  42         expandKey(key, c.enc, c.dec)
  43         return c, nil
  44 }
  45
  46 // BlockSize returns the AES block size, 16 bytes.
  47 // It is necessary to satisfy the Cipher interface in the
  48 // package "crypto/block".
  49 func (c *Cipher) BlockSize() int { return BlockSize }
  50
  51 // Encrypt encrypts the 16-byte buffer src using the key k
  52 // and stores the result in dst.
  53 // Note that for amounts of data larger than a block,
  54 // it is not safe to just call Encrypt on successive blocks;
  55 // instead, use an encryption mode like CBC (see crypto/block/cbc.go).
  56 func (c *Cipher) Encrypt(dst, src []byte) { encryptBlock(c.enc, dst, src) }
  57
  58 // Decrypt decrypts the 16-byte buffer src using the key k
  59 // and stores the result in dst.
  60 func (c *Cipher) Decrypt(dst, src []byte) { decryptBlock(c.dec, dst, src) }
  61
  62 // Reset zeros the key data, so that it will no longer
  63 // appear in the process's memory.
  64 func (c *Cipher) Reset() {
  65         for i := 0; i < len(c.enc); i++ {
  66                 c.enc[i] = 0
  67         }
  68         for i := 0; i < len(c.dec); i++ {
  69                 c.dec[i] = 0
  70         }
  71 }