| // Copyright 2010 The Go Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| // CFB (Cipher Feedback) Mode. |
| |
| package cipher |
| |
| type cfb struct { |
| b Block |
| out []byte |
| outUsed int |
| decrypt bool |
| } |
| |
| // NewCFBEncrypter returns a Stream which encrypts with cipher feedback mode, |
| // using the given Block. The iv must be the same length as the Block's block |
| // size. |
| func NewCFBEncrypter(block Block, iv []byte) Stream { |
| return newCFB(block, iv, false) |
| } |
| |
| // NewCFBDecrypter returns a Stream which decrypts with cipher feedback mode, |
| // using the given Block. The iv must be the same length as the Block's block |
| // size. |
| func NewCFBDecrypter(block Block, iv []byte) Stream { |
| return newCFB(block, iv, true) |
| } |
| |
| func newCFB(block Block, iv []byte, decrypt bool) Stream { |
| blockSize := block.BlockSize() |
| if len(iv) != blockSize { |
| return nil |
| } |
| |
| x := &cfb{ |
| b: block, |
| out: make([]byte, blockSize), |
| outUsed: 0, |
| decrypt: decrypt, |
| } |
| block.Encrypt(x.out, iv) |
| |
| return x |
| } |
| |
| func (x *cfb) XORKeyStream(dst, src []byte) { |
| for i := 0; i < len(src); i++ { |
| if x.outUsed == len(x.out) { |
| x.b.Encrypt(x.out, x.out) |
| x.outUsed = 0 |
| } |
| |
| if x.decrypt { |
| t := src[i] |
| dst[i] = src[i] ^ x.out[x.outUsed] |
| x.out[x.outUsed] = t |
| } else { |
| x.out[x.outUsed] ^= src[i] |
| dst[i] = x.out[x.outUsed] |
| } |
| x.outUsed++ |
| } |
| } |