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// 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++
}
}
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