1// Copyright 2022 The Go Authors. All rights reserved. 2// Use of this source code is governed by a BSD-style 3// license that can be found in the LICENSE file. 4 5//go:build (amd64 || arm64) && !purego 6 7package nistec_test 8 9import ( 10 "bytes" 11 "crypto/elliptic" 12 "crypto/internal/nistec" 13 "math/big" 14 "testing" 15) 16 17func TestP256OrdInverse(t *testing.T) { 18 N := elliptic.P256().Params().N 19 20 // inv(0) is expected to be 0. 21 zero := make([]byte, 32) 22 out, err := nistec.P256OrdInverse(zero) 23 if err != nil { 24 t.Fatal(err) 25 } 26 if !bytes.Equal(out, zero) { 27 t.Error("unexpected output for inv(0)") 28 } 29 30 // inv(N) is also 0 mod N. 31 input := make([]byte, 32) 32 N.FillBytes(input) 33 out, err = nistec.P256OrdInverse(input) 34 if err != nil { 35 t.Fatal(err) 36 } 37 if !bytes.Equal(out, zero) { 38 t.Error("unexpected output for inv(N)") 39 } 40 if !bytes.Equal(input, N.Bytes()) { 41 t.Error("input was modified") 42 } 43 44 // Check inv(1) and inv(N+1) against math/big 45 exp := new(big.Int).ModInverse(big.NewInt(1), N).FillBytes(make([]byte, 32)) 46 big.NewInt(1).FillBytes(input) 47 out, err = nistec.P256OrdInverse(input) 48 if err != nil { 49 t.Fatal(err) 50 } 51 if !bytes.Equal(out, exp) { 52 t.Error("unexpected output for inv(1)") 53 } 54 new(big.Int).Add(N, big.NewInt(1)).FillBytes(input) 55 out, err = nistec.P256OrdInverse(input) 56 if err != nil { 57 t.Fatal(err) 58 } 59 if !bytes.Equal(out, exp) { 60 t.Error("unexpected output for inv(N+1)") 61 } 62 63 // Check inv(20) and inv(N+20) against math/big 64 exp = new(big.Int).ModInverse(big.NewInt(20), N).FillBytes(make([]byte, 32)) 65 big.NewInt(20).FillBytes(input) 66 out, err = nistec.P256OrdInverse(input) 67 if err != nil { 68 t.Fatal(err) 69 } 70 if !bytes.Equal(out, exp) { 71 t.Error("unexpected output for inv(20)") 72 } 73 new(big.Int).Add(N, big.NewInt(20)).FillBytes(input) 74 out, err = nistec.P256OrdInverse(input) 75 if err != nil { 76 t.Fatal(err) 77 } 78 if !bytes.Equal(out, exp) { 79 t.Error("unexpected output for inv(N+20)") 80 } 81 82 // Check inv(2^256-1) against math/big 83 bigInput := new(big.Int).Lsh(big.NewInt(1), 256) 84 bigInput.Sub(bigInput, big.NewInt(1)) 85 exp = new(big.Int).ModInverse(bigInput, N).FillBytes(make([]byte, 32)) 86 bigInput.FillBytes(input) 87 out, err = nistec.P256OrdInverse(input) 88 if err != nil { 89 t.Fatal(err) 90 } 91 if !bytes.Equal(out, exp) { 92 t.Error("unexpected output for inv(2^256-1)") 93 } 94} 95