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// 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.
// Cipher block chaining (CBC) mode.
// CBC provides confidentiality by xoring (chaining) each plaintext block
// with the previous ciphertext block before applying the block cipher.
// See NIST SP 800-38A, pp 10-11
package cipher
type cbc struct {
b Block
blockSize int
iv []byte
tmp []byte
}
func newCBC(b Block, iv []byte) *cbc {
return &cbc{
b: b,
blockSize: b.BlockSize(),
iv: dup(iv),
tmp: make([]byte, b.BlockSize()),
}
}
type cbcEncrypter cbc
// NewCBCEncrypter returns a BlockMode which encrypts in cipher block chaining
// mode, using the given Block. The length of iv must be the same as the
// Block's block size.
func NewCBCEncrypter(b Block, iv []byte) BlockMode {
if len(iv) != b.BlockSize() {
panic("cipher.NewCBCEncrypter: IV length must equal block size")
}
return (*cbcEncrypter)(newCBC(b, iv))
}
func (x *cbcEncrypter) BlockSize() int { return x.blockSize }
func (x *cbcEncrypter) CryptBlocks(dst, src []byte) {
if len(src)%x.blockSize != 0 {
panic("crypto/cipher: input not full blocks")
}
if len(dst) < len(src) {
panic("crypto/cipher: output smaller than input")
}
for len(src) > 0 {
for i := 0; i < x.blockSize; i++ {
x.iv[i] ^= src[i]
}
x.b.Encrypt(x.iv, x.iv)
for i := 0; i < x.blockSize; i++ {
dst[i] = x.iv[i]
}
src = src[x.blockSize:]
dst = dst[x.blockSize:]
}
}
func (x *cbcEncrypter) SetIV(iv []byte) {
if len(iv) != len(x.iv) {
panic("cipher: incorrect length IV")
}
copy(x.iv, iv)
}
type cbcDecrypter cbc
// NewCBCDecrypter returns a BlockMode which decrypts in cipher block chaining
// mode, using the given Block. The length of iv must be the same as the
// Block's block size and must match the iv used to encrypt the data.
func NewCBCDecrypter(b Block, iv []byte) BlockMode {
if len(iv) != b.BlockSize() {
panic("cipher.NewCBCDecrypter: IV length must equal block size")
}
return (*cbcDecrypter)(newCBC(b, iv))
}
func (x *cbcDecrypter) BlockSize() int { return x.blockSize }
func (x *cbcDecrypter) CryptBlocks(dst, src []byte) {
if len(src)%x.blockSize != 0 {
panic("crypto/cipher: input not full blocks")
}
if len(dst) < len(src) {
panic("crypto/cipher: output smaller than input")
}
for len(src) > 0 {
x.b.Decrypt(x.tmp, src[:x.blockSize])
for i := 0; i < x.blockSize; i++ {
x.tmp[i] ^= x.iv[i]
x.iv[i] = src[i]
dst[i] = x.tmp[i]
}
src = src[x.blockSize:]
dst = dst[x.blockSize:]
}
}
func (x *cbcDecrypter) SetIV(iv []byte) {
if len(iv) != len(x.iv) {
panic("cipher: incorrect length IV")
}
copy(x.iv, iv)
}
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