go.crypto/poly1305: add package.
(Reference implementation by dchest. amd64 disabled pending 6l fix.)
R=golang-dev, dchest
CC=golang-dev
https://golang.org/cl/6494105
diff --git a/poly1305/poly1305.go b/poly1305/poly1305.go
new file mode 100644
index 0000000..2270d2b
--- /dev/null
+++ b/poly1305/poly1305.go
@@ -0,0 +1,32 @@
+// Copyright 2012 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.
+
+/*
+Package poly1305 implements Poly1305 one-time message authentication code as specified in http://cr.yp.to/mac/poly1305-20050329.pdf.
+
+Poly1305 is a fast, one-time authentication function. It is infeasible for an
+attacker to generate an authenticator for a message without the key. However, a
+key must only be used for a single message. Authenticating two different
+messages with the same key allows an attacker to forge authenticators for other
+messages with the same key.
+
+Poly1305 was originally coupled with AES in order to make Poly1305-AES. AES was
+used with a fixed key in order to generate one-time keys from an nonce.
+However, in this package AES isn't used and the one-time key is specified
+directly.
+*/
+package poly1305
+
+import "crypto/subtle"
+
+// TagSize is the size, in bytes, of a poly1305 authenticator.
+const TagSize = 16
+
+// Verify returns true if mac is a valid authenticator for m with the given
+// key.
+func Verify(mac *[16]byte, m []byte, key *[32]byte) bool {
+ var tmp [16]byte
+ Sum(&tmp, m, key)
+ return subtle.ConstantTimeCompare(tmp[:], mac[:]) == 1
+}
