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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
// import (
// "crypto/internal/alias"
// "crypto/subtle"
// )
// type cfb struct {
// b Block
// next []byte
// out []byte
// outUsed int
// decrypt bool
// }
// func (x *cfb) xor_key_stream(dst, src []byte) {
// if dst.len() < src.len() {
// panic("crypto/cipher: output smaller than input")
// }
// if alias.InexactOverlap(dst[..src.len()], src) {
// panic("crypto/cipher: invalid buffer overlap")
// }
// for src.len() > 0 {
// if x.outUsed == len(x.out) {
// x.b.encrypt(x.out, x.next)
// x.outUsed = 0
// }
// if x.decrypt {
// // We can precompute a larger segment of the
// // keystream on decryption. This will allow
// // larger batches for xor, and we should be
// // able to match CTR/OFB performance.
// copy(x.next[x.outUsed:], src)
// }
// n := subtle.XORBytes(dst, src, x.out[x.outUsed:])
// if !x.decrypt {
// copy(x.next[x.outUsed:], dst)
// }
// dst = dst[n:]
// src = src[n:]
// x.outUsed += n
// }
// }
// // 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.block_size()
// if len(iv) != blockSize {
// // stack trace will indicate whether it was de or encryption
// panic("cipher.newCFB: IV length must equal block size")
// }
// x := &cfb{
// b: block,
// out: make([]byte, blockSize),
// next: make([]byte, blockSize),
// outUsed: blockSize,
// decrypt: decrypt,
// }
// copy(x.next, iv)
// return x
// }