Add initial nistec project files

p256_ordinv_test.go

@@ -0,0 +1,95 @@
+// Copyright 2022 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 (amd64 || arm64) && !purego
+
+package nistec_test
+
+import (
+	"bytes"
+	"crypto/elliptic"
+	"math/big"
+	"testing"
+
+	"sources.truenas.cloud/code/nistec"
+)
+
+func TestP256OrdInverse(t *testing.T) {
+	N := elliptic.P256().Params().N
+
+	// inv(0) is expected to be 0.
+	zero := make([]byte, 32)
+	out, err := nistec.P256OrdInverse(zero)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(out, zero) {
+		t.Error("unexpected output for inv(0)")
+	}
+
+	// inv(N) is also 0 mod N.
+	input := make([]byte, 32)
+	N.FillBytes(input)
+	out, err = nistec.P256OrdInverse(input)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(out, zero) {
+		t.Error("unexpected output for inv(N)")
+	}
+	if !bytes.Equal(input, N.Bytes()) {
+		t.Error("input was modified")
+	}
+
+	// Check inv(1) and inv(N+1) against math/big
+	exp := new(big.Int).ModInverse(big.NewInt(1), N).FillBytes(make([]byte, 32))
+	big.NewInt(1).FillBytes(input)
+	out, err = nistec.P256OrdInverse(input)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(out, exp) {
+		t.Error("unexpected output for inv(1)")
+	}
+	new(big.Int).Add(N, big.NewInt(1)).FillBytes(input)
+	out, err = nistec.P256OrdInverse(input)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(out, exp) {
+		t.Error("unexpected output for inv(N+1)")
+	}
+
+	// Check inv(20) and inv(N+20) against math/big
+	exp = new(big.Int).ModInverse(big.NewInt(20), N).FillBytes(make([]byte, 32))
+	big.NewInt(20).FillBytes(input)
+	out, err = nistec.P256OrdInverse(input)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(out, exp) {
+		t.Error("unexpected output for inv(20)")
+	}
+	new(big.Int).Add(N, big.NewInt(20)).FillBytes(input)
+	out, err = nistec.P256OrdInverse(input)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(out, exp) {
+		t.Error("unexpected output for inv(N+20)")
+	}
+
+	// Check inv(2^256-1) against math/big
+	bigInput := new(big.Int).Lsh(big.NewInt(1), 256)
+	bigInput.Sub(bigInput, big.NewInt(1))
+	exp = new(big.Int).ModInverse(bigInput, N).FillBytes(make([]byte, 32))
+	bigInput.FillBytes(input)
+	out, err = nistec.P256OrdInverse(input)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(out, exp) {
+		t.Error("unexpected output for inv(2^256-1)")
+	}
+}