Gecko [ 167.86.127.34 ]

Name	Size	Permission
benchmark_test.go	3.46 KB	-rw-r--r--
cbc.go	4.42 KB	-rw-r--r--
cbc_aes_test.go	2.93 KB	-rw-r--r--
cfb.go	1.94 KB	-rw-r--r--
cfb_test.go	2.77 KB	-rw-r--r--
cipher.go	2.49 KB	-rw-r--r--
cipher_test.go	2.2 KB	-rw-r--r--
common_test.go	1.24 KB	-rw-r--r--
ctr.go	2.12 KB	-rw-r--r--
ctr_aes_test.go	2.98 KB	-rw-r--r--
ctr_test.go	1.13 KB	-rw-r--r--
example_test.go	11.78 KB	-rw-r--r--
export_test.go	242 B	-rw-r--r--
gcm.go	13.82 KB	-rw-r--r--
gcm_test.go	21.3 KB	-rw-r--r--
io.go	1.46 KB	-rw-r--r--
ofb.go	1.6 KB	-rw-r--r--
ofb_test.go	2.95 KB	-rw-r--r--
xor_amd64.go	642 B	-rw-r--r--
xor_amd64.s	1.31 KB	-rw-r--r--
xor_generic.go	2.33 KB	-rw-r--r--
xor_ppc64x.go	641 B	-rw-r--r--
xor_ppc64x.s	2.03 KB	-rw-r--r--
xor_test.go	1.6 KB	-rw-r--r--

Code Editor : ctr.go

// Copyright 2009 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.

// Counter (CTR) mode.

// CTR converts a block cipher into a stream cipher by
// repeatedly encrypting an incrementing counter and
// xoring the resulting stream of data with the input.

// See NIST SP 800-38A, pp 13-15

package cipher

import "crypto/internal/subtle"

type ctr struct {
	b       Block
	ctr     []byte
	out     []byte
	outUsed int
}

const streamBufferSize = 512

// ctrAble is an interface implemented by ciphers that have a specific optimized
// implementation of CTR, like crypto/aes. NewCTR will check for this interface
// and return the specific Stream if found.
type ctrAble interface {
	NewCTR(iv []byte) Stream
}

// NewCTR returns a Stream which encrypts/decrypts using the given Block in
// counter mode. The length of iv must be the same as the Block's block size.
func NewCTR(block Block, iv []byte) Stream {
	if ctr, ok := block.(ctrAble); ok {
		return ctr.NewCTR(iv)
	}
	if len(iv) != block.BlockSize() {
		panic("cipher.NewCTR: IV length must equal block size")
	}
	bufSize := streamBufferSize
	if bufSize < block.BlockSize() {
		bufSize = block.BlockSize()
	}
	return &ctr{
		b:       block,
		ctr:     dup(iv),
		out:     make([]byte, 0, bufSize),
		outUsed: 0,
	}
}

func (x *ctr) refill() {
	remain := len(x.out) - x.outUsed
	copy(x.out, x.out[x.outUsed:])
	x.out = x.out[:cap(x.out)]
	bs := x.b.BlockSize()
	for remain <= len(x.out)-bs {
		x.b.Encrypt(x.out[remain:], x.ctr)
		remain += bs

// Increment counter
		for i := len(x.ctr) - 1; i >= 0; i-- {
			x.ctr[i]++
			if x.ctr[i] != 0 {
				break
			}
		}
	}
	x.out = x.out[:remain]
	x.outUsed = 0
}

func (x *ctr) XORKeyStream(dst, src []byte) {
	if len(dst) < len(src) {
		panic("crypto/cipher: output smaller than input")
	}
	if subtle.InexactOverlap(dst[:len(src)], src) {
		panic("crypto/cipher: invalid buffer overlap")
	}
	for len(src) > 0 {
		if x.outUsed >= len(x.out)-x.b.BlockSize() {
			x.refill()
		}
		n := xorBytes(dst, src, x.out[x.outUsed:])
		dst = dst[n:]
		src = src[n:]
		x.outUsed += n
	}
}

${this.title}

Code Editor : ctr.go