vendor: update buildkit to f238f1e

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

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

@@ -2,21 +2,19 @@
 // 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 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 "golang.org/x/crypto/poly1305"
 
 import "crypto/subtle"
@@ -31,3 +29,55 @@ func Verify(mac *[16]byte, m []byte, key *[32]byte) bool {
 	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 {
+	return &MAC{
+		mac:       newMAC(key),
+		finalized: false,
+	}
+}
+
+// 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 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.
+func (h *MAC) Write(p []byte) (n int, err error) {
+	if h.finalized {
+		panic("poly1305: write to MAC after Sum")
+	}
+	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[:]...)
+}