vendor: update buildkit to 539be170

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

vendor/golang.org/x/crypto/internal/poly1305/poly1305.go

@@ -0,0 +1,99 @@
+// 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 https://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
+
+// Sum generates an authenticator for msg using a one-time key and puts the
+// 16-byte result into out. Authenticating two different messages with the same
+// key allows an attacker to forge messages at will.
+func Sum(out *[16]byte, m []byte, key *[32]byte) {
+	h := New(key)
+	h.Write(m)
+	h.Sum(out[:0])
+}
+
+// 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
+}
+
+// New returns a new MAC computing an authentication
+// tag of all data written to it with the given key.
+// This allows writing the message progressively instead
+// of passing it as a single slice. Common users should use
+// the Sum function instead.
+//
+// The key must be unique for each message, as authenticating
+// two different messages with the same key allows an attacker
+// to forge messages at will.
+func New(key *[32]byte) *MAC {
+	m := &MAC{}
+	initialize(key, &m.macState)
+	return m
+}
+
+// MAC is an io.Writer computing an authentication tag
+// of the data written to it.
+//
+// MAC cannot be used like common hash.Hash implementations,
+// because using a poly1305 key twice breaks its security.
+// Therefore writing data to a running MAC after calling
+// Sum or Verify causes it to panic.
+type MAC struct {
+	mac // platform-dependent implementation
+
+	finalized bool
+}
+
+// Size returns the number of bytes Sum will return.
+func (h *MAC) Size() int { return TagSize }
+
+// Write adds more data to the running message authentication code.
+// It never returns an error.
+//
+// It must not be called after the first call of Sum or Verify.
+func (h *MAC) Write(p []byte) (n int, err error) {
+	if h.finalized {
+		panic("poly1305: write to MAC after Sum or Verify")
+	}
+	return h.mac.Write(p)
+}
+
+// Sum computes the authenticator of all data written to the
+// message authentication code.
+func (h *MAC) Sum(b []byte) []byte {
+	var mac [TagSize]byte
+	h.mac.Sum(&mac)
+	h.finalized = true
+	return append(b, mac[:]...)
+}
+
+// Verify returns whether the authenticator of all data written to
+// the message authentication code matches the expected value.
+func (h *MAC) Verify(expected []byte) bool {
+	var mac [TagSize]byte
+	h.mac.Sum(&mac)
+	h.finalized = true
+	return subtle.ConstantTimeCompare(expected, mac[:]) == 1
+}