1 files changed, 10 insertions, 0 deletions
diff --git a/libgo/go/crypto/cipher/ctr.go b/libgo/go/crypto/cipher/ctr.go
index 16baa6d..75f46cf 100644
--- a/libgo/go/crypto/cipher/ctr.go
+++ b/libgo/go/crypto/cipher/ctr.go
@@ -21,9 +21,19 @@ type ctr struct {
 
 const streamBufferSize = 512
 
+// ctrAble is an interface implemented by ciphers that have a specific optimized
+// implementation of CTR, like crypto/aes. NewCTR will check for this interface
+// and return the specific Stream if found.
+type ctrAble interface {
+	NewCTR(iv []byte) Stream
+}
+
 // NewCTR returns a Stream which encrypts/decrypts using the given Block in
 // counter mode. The length of iv must be the same as the Block's block size.
 func NewCTR(block Block, iv []byte) Stream {
+	if ctr, ok := block.(ctrAble); ok {
+		return ctr.NewCTR(iv)
+	}
 	if len(iv) != block.BlockSize() {
 		panic("cipher.NewCTR: IV length must equal block size")
 	}