1 files changed, 96 insertions, 0 deletions
diff --git a/libgo/go/crypto/block/cfb.go b/libgo/go/crypto/block/cfb.go
new file mode 100644
index 000000000..f20c0a04f
--- /dev/null
+++ b/libgo/go/crypto/block/cfb.go
@@ -0,0 +1,96 @@
+// 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 feedback (CFB) mode.
+
+// CFB provides confidentiality by feeding a fraction of
+// the previous ciphertext in as the plaintext for the next
+// block operation.
+
+// See NIST SP 800-38A, pp 11-13
+
+package block
+
+import (
+	"io"
+)
+
+type cfbCipher struct {
+	c          Cipher
+	blockSize  int // our block size (s/8)
+	cipherSize int // underlying cipher block size
+	iv         []byte
+	tmp        []byte
+}
+
+func newCFB(c Cipher, s int, iv []byte) *cfbCipher {
+	if s == 0 || s%8 != 0 {
+		panic("crypto/block: invalid CFB mode")
+	}
+	b := c.BlockSize()
+	x := new(cfbCipher)
+	x.c = c
+	x.blockSize = s / 8
+	x.cipherSize = b
+	x.iv = dup(iv)
+	x.tmp = make([]byte, b)
+	return x
+}
+
+func (x *cfbCipher) BlockSize() int { return x.blockSize }
+
+func (x *cfbCipher) Encrypt(dst, src []byte) {
+	// Encrypt old IV and xor prefix with src to make dst.
+	x.c.Encrypt(x.tmp, x.iv)
+	for i := 0; i < x.blockSize; i++ {
+		dst[i] = src[i] ^ x.tmp[i]
+	}
+
+	// Slide unused IV pieces down and insert dst at end.
+	for i := 0; i < x.cipherSize-x.blockSize; i++ {
+		x.iv[i] = x.iv[i+x.blockSize]
+	}
+	off := x.cipherSize - x.blockSize
+	for i := off; i < x.cipherSize; i++ {
+		x.iv[i] = dst[i-off]
+	}
+}
+
+func (x *cfbCipher) Decrypt(dst, src []byte) {
+	// Encrypt [sic] old IV and xor prefix with src to make dst.
+	x.c.Encrypt(x.tmp, x.iv)
+	for i := 0; i < x.blockSize; i++ {
+		dst[i] = src[i] ^ x.tmp[i]
+	}
+
+	// Slide unused IV pieces down and insert src at top.
+	for i := 0; i < x.cipherSize-x.blockSize; i++ {
+		x.iv[i] = x.iv[i+x.blockSize]
+	}
+	off := x.cipherSize - x.blockSize
+	for i := off; i < x.cipherSize; i++ {
+		// Reconstruct src = dst ^ x.tmp
+		// in case we overwrote src (src == dst).
+		x.iv[i] = dst[i-off] ^ x.tmp[i-off]
+	}
+}
+
+// NewCFBDecrypter returns a reader that reads data from r and decrypts it using c
+// in s-bit cipher feedback (CFB) mode with the initialization vector iv.
+// The returned Reader does not buffer or read ahead except
+// as required by the cipher's block size.
+// Modes for s not a multiple of 8 are unimplemented.
+func NewCFBDecrypter(c Cipher, s int, iv []byte, r io.Reader) io.Reader {
+	return NewECBDecrypter(newCFB(c, s, iv), r)
+}
+
+// NewCFBEncrypter returns a writer that encrypts data using c
+// in s-bit cipher feedback (CFB) 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.
+// Modes for s not a multiple of 8 are unimplemented.
+func NewCFBEncrypter(c Cipher, s int, iv []byte, w io.Writer) io.Writer {
+	return NewECBEncrypter(newCFB(c, s, iv), w)
+}