1 files changed, 67 insertions, 0 deletions
diff --git a/libgo/go/crypto/block/ctr.go b/libgo/go/crypto/block/ctr.go
new file mode 100644
index 000000000..5d65c0c9a
--- /dev/null
+++ b/libgo/go/crypto/block/ctr.go
@@ -0,0 +1,67 @@
+// 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.
+
+// Counter (CTR) mode.
+
+// CTR converts a block cipher into a stream cipher by
+// repeatedly encrypting an incrementing counter and
+// xoring the resulting stream of data with the input.
+
+// See NIST SP 800-38A, pp 13-15
+
+package block
+
+import (
+	"io"
+)
+
+type ctrStream struct {
+	c   Cipher
+	ctr []byte
+	out []byte
+}
+
+func newCTRStream(c Cipher, ctr []byte) *ctrStream {
+	x := new(ctrStream)
+	x.c = c
+	x.ctr = dup(ctr)
+	x.out = make([]byte, len(ctr))
+	return x
+}
+
+func (x *ctrStream) Next() []byte {
+	// Next block is encryption of counter.
+	x.c.Encrypt(x.out, x.ctr)
+
+	// Increment counter
+	for i := len(x.ctr) - 1; i >= 0; i-- {
+		x.ctr[i]++
+		if x.ctr[i] != 0 {
+			break
+		}
+	}
+
+	return x.out
+}
+
+// NewCTRReader returns a reader that reads data from r, decrypts (or encrypts)
+// it using c in counter (CTR) mode with the initialization vector iv.
+// The returned Reader does not buffer and has no block size.
+// In CTR mode, encryption and decryption are the same operation:
+// a CTR reader applied to an encrypted stream produces a decrypted
+// stream and vice versa.
+func NewCTRReader(c Cipher, iv []byte, r io.Reader) io.Reader {
+	return newXorReader(newCTRStream(c, iv), r)
+}
+
+// NewCTRWriter returns a writer that encrypts (or decrypts) data using c
+// in counter (CTR) 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 CTR mode, encryption and decryption are the same operation:
+// a CTR writer applied to an decrypted stream produces an encrypted
+// stream and vice versa.
+func NewCTRWriter(c Cipher, iv []byte, w io.Writer) io.Writer {
+	return newXorWriter(newCTRStream(c, iv), w)
+}