1 // Copyright 2012 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
5 // Package poly1305 implements Poly1305 one-time message authentication code as
6 // specified in https://cr.yp.to/mac/poly1305-20050329.pdf.
8 // Poly1305 is a fast, one-time authentication function. It is infeasible for an
9 // attacker to generate an authenticator for a message without the key. However, a
10 // key must only be used for a single message. Authenticating two different
11 // messages with the same key allows an attacker to forge authenticators for other
12 // messages with the same key.
14 // Poly1305 was originally coupled with AES in order to make Poly1305-AES. AES was
15 // used with a fixed key in order to generate one-time keys from an nonce.
16 // However, in this package AES isn't used and the one-time key is specified
18 package poly1305 // import "golang.org/x/crypto/poly1305"
20 import "crypto/subtle"
22 // TagSize is the size, in bytes, of a poly1305 authenticator.
25 // Verify returns true if mac is a valid authenticator for m with the given
27 func Verify(mac *[16]byte, m []byte, key *[32]byte) bool {
30 return subtle.ConstantTimeCompare(tmp[:], mac[:]) == 1
33 // New returns a new MAC computing an authentication
34 // tag of all data written to it with the given key.
35 // This allows writing the message progressively instead
36 // of passing it as a single slice. Common users should use
37 // the Sum function instead.
39 // The key must be unique for each message, as authenticating
40 // two different messages with the same key allows an attacker
41 // to forge messages at will.
42 func New(key *[32]byte) *MAC {
49 // MAC is an io.Writer computing an authentication tag
50 // of the data written to it.
52 // MAC cannot be used like common hash.Hash implementations,
53 // because using a poly1305 key twice breaks its security.
54 // Therefore writing data to a running MAC after calling
55 // Sum causes it to panic.
57 mac // platform-dependent implementation
62 // Size returns the number of bytes Sum will return.
63 func (h *MAC) Size() int { return TagSize }
65 // Write adds more data to the running message authentication code.
66 // It never returns an error.
68 // It must not be called after the first call of Sum.
69 func (h *MAC) Write(p []byte) (n int, err error) {
71 panic("poly1305: write to MAC after Sum")
76 // Sum computes the authenticator of all data written to the
77 // message authentication code.
78 func (h *MAC) Sum(b []byte) []byte {
82 return append(b, mac[:]...)