1 files changed, 71 insertions, 0 deletions
diff --git a/libgo/go/crypto/block/cbc.go b/libgo/go/crypto/block/cbc.go
new file mode 100644
index 000000000..23229c09f
--- /dev/null
+++ b/libgo/go/crypto/block/cbc.go
@@ -0,0 +1,71 @@
+// 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 block
+
+import (
+	"io"
+)
+
+type cbcCipher struct {
+	c         Cipher
+	blockSize int
+	iv        []byte
+	tmp       []byte
+}
+
+func newCBC(c Cipher, iv []byte) *cbcCipher {
+	n := c.BlockSize()
+	x := new(cbcCipher)
+	x.c = c
+	x.blockSize = n
+	x.iv = dup(iv)
+	x.tmp = make([]byte, n)
+	return x
+}
+
+func (x *cbcCipher) BlockSize() int { return x.blockSize }
+
+func (x *cbcCipher) Encrypt(dst, src []byte) {
+	for i := 0; i < x.blockSize; i++ {
+		x.iv[i] ^= src[i]
+	}
+	x.c.Encrypt(x.iv, x.iv)
+	for i := 0; i < x.blockSize; i++ {
+		dst[i] = x.iv[i]
+	}
+}
+
+func (x *cbcCipher) Decrypt(dst, src []byte) {
+	x.c.Decrypt(x.tmp, src)
+	for i := 0; i < x.blockSize; i++ {
+		x.tmp[i] ^= x.iv[i]
+		x.iv[i] = src[i]
+		dst[i] = x.tmp[i]
+	}
+}
+
+// NewCBCDecrypter returns a reader that reads data from r and decrypts it using c
+// in cipher block chaining (CBC) mode with the initialization vector iv.
+// The returned Reader does not buffer or read ahead except
+// as required by the cipher's block size.
+func NewCBCDecrypter(c Cipher, iv []byte, r io.Reader) io.Reader {
+	return NewECBDecrypter(newCBC(c, iv), r)
+}
+
+// NewCBCEncrypter returns a writer that encrypts data using c
+// in cipher block chaining (CBC) mode with the initialization vector iv
+// and writes the encrypted data to w.
+// The returned Writer does no buffering except as required
+// by the cipher's block size, so there is no need for a Flush method.
+func NewCBCEncrypter(c Cipher, iv []byte, w io.Writer) io.Writer {
+	return NewECBEncrypter(newCBC(c, iv), w)
+}