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// Copyright 2011 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.
// OFB (Output Feedback) Mode.
package cipher
type ofb struct {
b Block
out []byte
outUsed int
}
// NewOFB returns a Stream that encrypts or decrypts using the block cipher b
// in output feedback mode. The initialization vector iv's length must be equal
// to b's block size.
func NewOFB(b Block, iv []byte) Stream {
blockSize := b.BlockSize()
if len(iv) != blockSize {
return nil
}
x := &ofb{
b: b,
out: make([]byte, blockSize),
outUsed: 0,
}
b.Encrypt(x.out, iv)
return x
}
func (x *ofb) XORKeyStream(dst, src []byte) {
for i, s := range src {
if x.outUsed == len(x.out) {
x.b.Encrypt(x.out, x.out)
x.outUsed = 0
}
dst[i] = s ^ x.out[x.outUsed]
x.outUsed++
}
}
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