update vendor keybase/go-crypto (#10234)

vendor/github.com/keybase/go-crypto/curve25519/curve25519.go

@@ -2,12 +2,16 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// We have a implementation in amd64 assembly so this code is only run on
+// We have an implementation in amd64 assembly so this code is only run on
 // non-amd64 platforms. The amd64 assembly does not support gccgo.
 // +build !amd64 gccgo appengine
 
 package curve25519
 
+import (
+	"encoding/binary"
+)
+
 // This code is a port of the public domain, "ref10" implementation of
 // curve25519 from SUPERCOP 20130419 by D. J. Bernstein.
 
@@ -50,17 +54,11 @@ func feCopy(dst, src *fieldElement) {
 //
 // Preconditions: b in {0,1}.
 func feCSwap(f, g *fieldElement, b int32) {
-	var x fieldElement
 	b = -b
-	for i := range x {
-		x[i] = b & (f[i] ^ g[i])
-	}
-
 	for i := range f {
-		f[i] ^= x[i]
-	}
-	for i := range g {
-		g[i] ^= x[i]
+		t := b & (f[i] ^ g[i])
+		f[i] ^= t
+		g[i] ^= t
 	}
 }
 
@@ -75,12 +73,7 @@ func load3(in []byte) int64 {
 
 // load4 reads a 32-bit, little-endian value from in.
 func load4(in []byte) int64 {
-	var r int64
-	r = int64(in[0])
-	r |= int64(in[1]) << 8
-	r |= int64(in[2]) << 16
-	r |= int64(in[3]) << 24
-	return r
+	return int64(binary.LittleEndian.Uint32(in))
 }
 
 func feFromBytes(dst *fieldElement, src *[32]byte) {