1 files changed, 60 insertions, 0 deletions
diff --git a/libgo/go/crypto/block/ofb.go b/libgo/go/crypto/block/ofb.go
new file mode 100644
index 000000000..11aaaa4d7
--- /dev/null
+++ b/libgo/go/crypto/block/ofb.go
@@ -0,0 +1,60 @@
+// 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.
+
+// Output feedback (OFB) mode.
+
+// OFB converts a block cipher into a stream cipher by
+// repeatedly encrypting an initialization vector and
+// xoring the resulting stream of data with the input.
+
+// See NIST SP 800-38A, pp 13-15
+
+package block
+
+import (
+	"fmt"
+	"io"
+)
+
+type ofbStream struct {
+	c  Cipher
+	iv []byte
+}
+
+func newOFBStream(c Cipher, iv []byte) *ofbStream {
+	x := new(ofbStream)
+	x.c = c
+	n := len(iv)
+	if n != c.BlockSize() {
+		panic(fmt.Sprintln("crypto/block: newOFBStream: invalid iv size", n, "!=", c.BlockSize()))
+	}
+	x.iv = dup(iv)
+	return x
+}
+
+func (x *ofbStream) Next() []byte {
+	x.c.Encrypt(x.iv, x.iv)
+	return x.iv
+}
+
+// NewOFBReader returns a reader that reads data from r, decrypts (or encrypts)
+// it using c in output feedback (OFB) mode with the initialization vector iv.
+// The returned Reader does not buffer and has no block size.
+// In OFB mode, encryption and decryption are the same operation:
+// an OFB reader applied to an encrypted stream produces a decrypted
+// stream and vice versa.
+func NewOFBReader(c Cipher, iv []byte, r io.Reader) io.Reader {
+	return newXorReader(newOFBStream(c, iv), r)
+}
+
+// NewOFBWriter returns a writer that encrypts (or decrypts) data using c
+// in cipher feedback (OFB) mode with the initialization vector iv
+// and writes the encrypted data to w.
+// The returned Writer does not buffer and has no block size.
+// In OFB mode, encryption and decryption are the same operation:
+// an OFB writer applied to an decrypted stream produces an encrypted
+// stream and vice versa.
+func NewOFBWriter(c Cipher, iv []byte, w io.Writer) io.Writer {
+	return newXorWriter(newOFBStream(c, iv), w)
+}