1 files changed, 32 insertions, 10 deletions
diff --git a/src/pkg/crypto/cipher/ofb.go b/src/pkg/crypto/cipher/ofb.go
index 85e5f02b0..e86ebcb23 100644
--- a/src/pkg/crypto/cipher/ofb.go
+++ b/src/pkg/crypto/cipher/ofb.go
@@ -8,6 +8,7 @@ package cipher
 
 type ofb struct {
 	b       Block
+	cipher  []byte
 	out     []byte
 	outUsed int
 }
@@ -20,25 +21,46 @@ func NewOFB(b Block, iv []byte) Stream {
 	if len(iv) != blockSize {
 		return nil
 	}
-
+	bufSize := streamBufferSize
+	if bufSize < blockSize {
+		bufSize = blockSize
+	}
 	x := &ofb{
 		b:       b,
-		out:     make([]byte, blockSize),
+		cipher:  make([]byte, blockSize),
+		out:     make([]byte, 0, bufSize),
 		outUsed: 0,
 	}
-	b.Encrypt(x.out, iv)
 
+	copy(x.cipher, iv)
 	return x
 }
 
+func (x *ofb) refill() {
+	bs := x.b.BlockSize()
+	remain := len(x.out) - x.outUsed
+	if remain > x.outUsed {
+		return
+	}
+	copy(x.out, x.out[x.outUsed:])
+	x.out = x.out[:cap(x.out)]
+	for remain < len(x.out)-bs {
+		x.b.Encrypt(x.cipher, x.cipher)
+		copy(x.out[remain:], x.cipher)
+		remain += bs
+	}
+	x.out = x.out[:remain]
+	x.outUsed = 0
+}
+
 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
+	for len(src) > 0 {
+		if x.outUsed >= len(x.out)-x.b.BlockSize() {
+			x.refill()
 		}
-
-		dst[i] = s ^ x.out[x.outUsed]
-		x.outUsed++
+		n := xorBytes(dst, src, x.out[x.outUsed:])
+		dst = dst[n:]
+		src = src[n:]
+		x.outUsed += n
 	}
 }