vendor: update buildkit to master@d5c1d785b042

Signed-off-by: Justin Chadwell <me@jedevc.com>

vendor/golang.org/x/crypto/curve25519/curve25519_compat.go

@@ -0,0 +1,105 @@
+// Copyright 2019 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.
+
+//go:build !go1.20
+
+package curve25519
+
+import (
+	"crypto/subtle"
+	"errors"
+	"strconv"
+
+	"golang.org/x/crypto/curve25519/internal/field"
+)
+
+func scalarMult(dst, scalar, point *[32]byte) {
+	var e [32]byte
+
+	copy(e[:], scalar[:])
+	e[0] &= 248
+	e[31] &= 127
+	e[31] |= 64
+
+	var x1, x2, z2, x3, z3, tmp0, tmp1 field.Element
+	x1.SetBytes(point[:])
+	x2.One()
+	x3.Set(&x1)
+	z3.One()
+
+	swap := 0
+	for pos := 254; pos >= 0; pos-- {
+		b := e[pos/8] >> uint(pos&7)
+		b &= 1
+		swap ^= int(b)
+		x2.Swap(&x3, swap)
+		z2.Swap(&z3, swap)
+		swap = int(b)
+
+		tmp0.Subtract(&x3, &z3)
+		tmp1.Subtract(&x2, &z2)
+		x2.Add(&x2, &z2)
+		z2.Add(&x3, &z3)
+		z3.Multiply(&tmp0, &x2)
+		z2.Multiply(&z2, &tmp1)
+		tmp0.Square(&tmp1)
+		tmp1.Square(&x2)
+		x3.Add(&z3, &z2)
+		z2.Subtract(&z3, &z2)
+		x2.Multiply(&tmp1, &tmp0)
+		tmp1.Subtract(&tmp1, &tmp0)
+		z2.Square(&z2)
+
+		z3.Mult32(&tmp1, 121666)
+		x3.Square(&x3)
+		tmp0.Add(&tmp0, &z3)
+		z3.Multiply(&x1, &z2)
+		z2.Multiply(&tmp1, &tmp0)
+	}
+
+	x2.Swap(&x3, swap)
+	z2.Swap(&z3, swap)
+
+	z2.Invert(&z2)
+	x2.Multiply(&x2, &z2)
+	copy(dst[:], x2.Bytes())
+}
+
+func scalarBaseMult(dst, scalar *[32]byte) {
+	checkBasepoint()
+	scalarMult(dst, scalar, &basePoint)
+}
+
+func x25519(dst *[32]byte, scalar, point []byte) ([]byte, error) {
+	var in [32]byte
+	if l := len(scalar); l != 32 {
+		return nil, errors.New("bad scalar length: " + strconv.Itoa(l) + ", expected 32")
+	}
+	if l := len(point); l != 32 {
+		return nil, errors.New("bad point length: " + strconv.Itoa(l) + ", expected 32")
+	}
+	copy(in[:], scalar)
+	if &point[0] == &Basepoint[0] {
+		scalarBaseMult(dst, &in)
+	} else {
+		var base, zero [32]byte
+		copy(base[:], point)
+		scalarMult(dst, &in, &base)
+		if subtle.ConstantTimeCompare(dst[:], zero[:]) == 1 {
+			return nil, errors.New("bad input point: low order point")
+		}
+	}
+	return dst[:], nil
+}
+
+func checkBasepoint() {
+	if subtle.ConstantTimeCompare(Basepoint, []byte{
+		0x09, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+	}) != 1 {
+		panic("curve25519: global Basepoint value was modified")
+	}
+}