1 files changed, 124 insertions, 0 deletions
diff --git a/libgo/go/crypto/block/xor.go b/libgo/go/crypto/block/xor.go
new file mode 100644
index 000000000..9d8b17224
--- /dev/null
+++ b/libgo/go/crypto/block/xor.go
@@ -0,0 +1,124 @@
+// 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.
+
+// Encrypt/decrypt data by xor with a pseudo-random data stream.
+
+package block
+
+import (
+	"io"
+	"os"
+)
+
+// A dataStream is an interface to an unending stream of data,
+// used by XorReader and XorWriter to model a pseudo-random generator.
+// Calls to Next() return sequential blocks of data from the stream.
+// Each call must return at least one byte: there is no EOF.
+type dataStream interface {
+	Next() []byte
+}
+
+type xorReader struct {
+	r    io.Reader
+	rand dataStream // pseudo-random
+	buf  []byte     // data available from last call to rand
+}
+
+func newXorReader(rand dataStream, r io.Reader) io.Reader {
+	x := new(xorReader)
+	x.r = r
+	x.rand = rand
+	return x
+}
+
+func (x *xorReader) Read(p []byte) (n int, err os.Error) {
+	n, err = x.r.Read(p)
+
+	// xor input with stream.
+	bp := 0
+	buf := x.buf
+	for i := 0; i < n; i++ {
+		if bp >= len(buf) {
+			buf = x.rand.Next()
+			bp = 0
+		}
+		p[i] ^= buf[bp]
+		bp++
+	}
+	x.buf = buf[bp:]
+	return n, err
+}
+
+type xorWriter struct {
+	w     io.Writer
+	rand  dataStream // pseudo-random
+	buf   []byte     // last buffer returned by rand
+	extra []byte     // extra random data (use before buf)
+	work  []byte     // work space
+}
+
+func newXorWriter(rand dataStream, w io.Writer) io.Writer {
+	x := new(xorWriter)
+	x.w = w
+	x.rand = rand
+	x.work = make([]byte, 4096)
+	return x
+}
+
+func (x *xorWriter) Write(p []byte) (n int, err os.Error) {
+	for len(p) > 0 {
+		// Determine next chunk of random data
+		// and xor with p into x.work.
+		var chunk []byte
+		m := len(p)
+		if nn := len(x.extra); nn > 0 {
+			// extra points into work, so edit directly
+			if m > nn {
+				m = nn
+			}
+			for i := 0; i < m; i++ {
+				x.extra[i] ^= p[i]
+			}
+			chunk = x.extra[0:m]
+		} else {
+			// xor p ^ buf into work, refreshing buf as needed
+			if nn := len(x.work); m > nn {
+				m = nn
+			}
+			bp := 0
+			buf := x.buf
+			for i := 0; i < m; i++ {
+				if bp >= len(buf) {
+					buf = x.rand.Next()
+					bp = 0
+				}
+				x.work[i] = buf[bp] ^ p[i]
+				bp++
+			}
+			x.buf = buf[bp:]
+			chunk = x.work[0:m]
+		}
+
+		// Write chunk.
+		var nn int
+		nn, err = x.w.Write(chunk)
+		if nn != len(chunk) && err == nil {
+			err = io.ErrShortWrite
+		}
+		if nn < len(chunk) {
+			// Reconstruct the random bits from the unwritten
+			// data and save them for next time.
+			for i := nn; i < m; i++ {
+				chunk[i] ^= p[i]
+			}
+			x.extra = chunk[nn:]
+		}
+		n += nn
+		if err != nil {
+			return
+		}
+		p = p[m:]
+	}
+	return
+}