Imported Upstream version 2011-02-01.1upstream/2011-02-01.1

1 files changed, 44 insertions, 0 deletions

diff --git a/src/pkg/crypto/cipher/ofb.go b/src/pkg/crypto/cipher/ofb.go
new file mode 100644
index 000000000..85e5f02b0
--- /dev/null
+++ b/src/pkg/crypto/cipher/ofb.go
@@ -0,0 +1,44 @@
+// Copyright 2011 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.
+
+// OFB (Output Feedback) Mode.
+
+package cipher
+
+type ofb struct {
+	b       Block
+	out     []byte
+	outUsed int
+}
+
+// NewOFB returns a Stream that encrypts or decrypts using the block cipher b
+// in output feedback mode. The initialization vector iv's length must be equal
+// to b's block size.
+func NewOFB(b Block, iv []byte) Stream {
+	blockSize := b.BlockSize()
+	if len(iv) != blockSize {
+		return nil
+	}
+
+	x := &ofb{
+		b:       b,
+		out:     make([]byte, blockSize),
+		outUsed: 0,
+	}
+	b.Encrypt(x.out, iv)
+
+	return x
+}
+
+func (x *ofb) XORKeyStream(dst, src []byte) {
+	for i, s := range src {
+		if x.outUsed == len(x.out) {
+			x.b.Encrypt(x.out, x.out)
+			x.outUsed = 0
+		}
+
+		dst[i] = s ^ x.out[x.outUsed]
+		x.outUsed++
+	}
+}