dd931d9b48
Reviewed-on: https://go-review.googlesource.com/136435 gotools/: * Makefile.am (mostlyclean-local): Run chmod on check-go-dir to make sure it is writable. (check-go-tools): Likewise. (check-vet): Copy internal/objabi to check-vet-dir. * Makefile.in: Rebuild. From-SVN: r264546
75 lines
1.6 KiB
Go
75 lines
1.6 KiB
Go
// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// OFB (Output Feedback) Mode.
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package cipher
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import "crypto/internal/subtle"
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type ofb struct {
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b Block
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cipher []byte
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out []byte
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outUsed int
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}
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// NewOFB returns a Stream that encrypts or decrypts using the block cipher b
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// in output feedback mode. The initialization vector iv's length must be equal
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// to b's block size.
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func NewOFB(b Block, iv []byte) Stream {
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blockSize := b.BlockSize()
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if len(iv) != blockSize {
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panic("cipher.NewOFB: IV length must equal block size")
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}
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bufSize := streamBufferSize
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if bufSize < blockSize {
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bufSize = blockSize
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}
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x := &ofb{
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b: b,
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cipher: make([]byte, blockSize),
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out: make([]byte, 0, bufSize),
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outUsed: 0,
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}
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copy(x.cipher, iv)
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return x
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}
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func (x *ofb) refill() {
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bs := x.b.BlockSize()
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remain := len(x.out) - x.outUsed
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if remain > x.outUsed {
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return
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}
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copy(x.out, x.out[x.outUsed:])
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x.out = x.out[:cap(x.out)]
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for remain < len(x.out)-bs {
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x.b.Encrypt(x.cipher, x.cipher)
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copy(x.out[remain:], x.cipher)
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remain += bs
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}
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x.out = x.out[:remain]
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x.outUsed = 0
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}
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func (x *ofb) XORKeyStream(dst, src []byte) {
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if len(dst) < len(src) {
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panic("crypto/cipher: output smaller than input")
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}
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if subtle.InexactOverlap(dst[:len(src)], src) {
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panic("crypto/cipher: invalid buffer overlap")
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}
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for len(src) > 0 {
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if x.outUsed >= len(x.out)-x.b.BlockSize() {
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x.refill()
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}
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n := xorBytes(dst, src, x.out[x.outUsed:])
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dst = dst[n:]
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src = src[n:]
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x.outUsed += n
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}
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}
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