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sm2ec.go
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sm2ec.go
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package ecdh
import (
"encoding/binary"
"errors"
"hash"
"io"
"math/bits"
"github.com/emmansun/gmsm/internal/randutil"
sm2ec "github.com/emmansun/gmsm/internal/sm2ec"
"github.com/emmansun/gmsm/internal/subtle"
)
type sm2Curve struct {
name string
newPoint func() *sm2ec.SM2P256Point
scalarOrderMinus1 []byte
constantA []byte
constantB []byte
generator []byte
}
func (c *sm2Curve) String() string {
return c.name
}
func (c *sm2Curve) GenerateKey(rand io.Reader) (*PrivateKey, error) {
key := make([]byte, len(c.scalarOrderMinus1))
randutil.MaybeReadByte(rand)
for {
if _, err := io.ReadFull(rand, key); err != nil {
return nil, err
}
// In tests, rand will return all zeros and NewPrivateKey will reject
// the zero key as it generates the identity as a public key. This also
// makes this function consistent with crypto/elliptic.GenerateKey.
key[1] ^= 0x42
k, err := c.NewPrivateKey(key)
if err == errInvalidPrivateKey {
continue
}
return k, err
}
}
func (c *sm2Curve) NewPrivateKey(key []byte) (*PrivateKey, error) {
if len(key) != len(c.scalarOrderMinus1) {
return nil, errors.New("ecdh: invalid private key size")
}
if subtle.ConstantTimeAllZero(key) || !isLess(key, c.scalarOrderMinus1) {
return nil, errInvalidPrivateKey
}
return &PrivateKey{
curve: c,
privateKey: append([]byte{}, key...),
}, nil
}
func (c *sm2Curve) privateKeyToPublicKey(key *PrivateKey) *PublicKey {
if key.curve != c {
panic("ecdh: internal error: converting the wrong key type")
}
p, err := c.newPoint().ScalarBaseMult(key.privateKey)
if err != nil {
// This is unreachable because the only error condition of
// ScalarBaseMult is if the input is not the right size.
panic("ecdh: internal error: sm2ec ScalarBaseMult failed for a fixed-size input")
}
publicKey := p.Bytes()
if len(publicKey) == 1 {
// The encoding of the identity is a single 0x00 byte. This is
// unreachable because the only scalar that generates the identity is
// zero, which is rejected by NewPrivateKey.
panic("ecdh: internal error: sm2ec ScalarBaseMult returned the identity")
}
return &PublicKey{
curve: key.curve,
publicKey: publicKey,
}
}
func (c *sm2Curve) NewPublicKey(key []byte) (*PublicKey, error) {
// Reject the point at infinity and compressed encodings.
if len(key) == 0 || key[0] != 4 {
return nil, errors.New("ecdh: invalid public key")
}
// SetBytes also checks that the point is on the curve.
if _, err := c.newPoint().SetBytes(key); err != nil {
return nil, err
}
return &PublicKey{
curve: c,
publicKey: append([]byte{}, key...),
}, nil
}
func (c *sm2Curve) ecdh(local *PrivateKey, remote *PublicKey) ([]byte, error) {
p, err := c.newPoint().SetBytes(remote.publicKey)
if err != nil {
return nil, err
}
if _, err := p.ScalarMult(p, local.privateKey); err != nil {
return nil, err
}
// BytesX will return an error if p is the point at infinity.
return p.BytesX()
}
func (c *sm2Curve) sm2avf(secret *PublicKey) []byte {
bytes := secret.publicKey[1:33]
var result [32]byte
copy(result[16:], bytes[16:])
result[16] = (result[16] & 0x7f) | 0x80
return result[:]
}
func (c *sm2Curve) sm2mqv(sLocal, eLocal *PrivateKey, sRemote, eRemote *PublicKey) (*PublicKey, error) {
// implicitSig: (sLocal + avf(eLocal.Pub) * ePriv) mod N
x2 := c.sm2avf(eLocal.PublicKey())
t, err := sm2ec.ImplicitSig(sLocal.privateKey, eLocal.privateKey, x2)
if err != nil {
return nil, err
}
// new base point: peerPub + [x1](peerSecret)
x1 := c.sm2avf(eRemote)
p2, err := c.newPoint().SetBytes(eRemote.publicKey)
if err != nil {
return nil, err
}
if _, err := p2.ScalarMult(p2, x1); err != nil {
return nil, err
}
p1, err := c.newPoint().SetBytes(sRemote.publicKey)
if err != nil {
return nil, err
}
p2.Add(p1, p2)
if _, err := p2.ScalarMult(p2, t); err != nil {
return nil, err
}
return c.NewPublicKey(p2.Bytes())
}
var defaultUID = []byte{0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38}
// CalculateZA ZA = H256(ENTLA || IDA || a || b || xG || yG || xA || yA).
// Compliance with GB/T 32918.2-2016 5.5
func (c *sm2Curve) sm2za(md hash.Hash, pub *PublicKey, uid []byte) ([]byte, error) {
if len(uid) == 0 {
uid = defaultUID
}
uidLen := len(uid)
if uidLen >= 0x2000 {
return nil, errors.New("ecdh: the uid is too long")
}
entla := uint16(uidLen) << 3
md.Write([]byte{byte(entla >> 8), byte(entla)})
if uidLen > 0 {
md.Write(uid)
}
md.Write(c.constantA)
md.Write(c.constantB)
md.Write(c.generator)
md.Write(pub.publicKey[1:])
return md.Sum(nil), nil
}
// P256 returns a Curve which implements SM2, also known as sm2p256v1
//
// Multiple invocations of this function will return the same value, so it can
// be used for equality checks and switch statements.
func P256() Curve { return sm2P256 }
var sm2P256 = &sm2Curve{
name: "sm2p256v1",
newPoint: sm2ec.NewSM2P256Point,
scalarOrderMinus1: sm2P256OrderMinus1,
generator: sm2Generator,
constantA: sm2ConstantA,
constantB: sm2ConstantB,
}
var sm2P256OrderMinus1 = []byte{
0xff, 0xff, 0xff, 0xfe, 0xff, 0xff, 0xff, 0xff,
0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
0x72, 0x03, 0xdf, 0x6b, 0x21, 0xc6, 0x05, 0x2b,
0x53, 0xbb, 0xf4, 0x09, 0x39, 0xd5, 0x41, 0x22}
var sm2Generator = []byte{
0x32, 0xc4, 0xae, 0x2c, 0x1f, 0x19, 0x81, 0x19,
0x5f, 0x99, 0x4, 0x46, 0x6a, 0x39, 0xc9, 0x94,
0x8f, 0xe3, 0xb, 0xbf, 0xf2, 0x66, 0xb, 0xe1,
0x71, 0x5a, 0x45, 0x89, 0x33, 0x4c, 0x74, 0xc7,
0xbc, 0x37, 0x36, 0xa2, 0xf4, 0xf6, 0x77, 0x9c,
0x59, 0xbd, 0xce, 0xe3, 0x6b, 0x69, 0x21, 0x53,
0xd0, 0xa9, 0x87, 0x7c, 0xc6, 0x2a, 0x47, 0x40,
0x2, 0xdf, 0x32, 0xe5, 0x21, 0x39, 0xf0, 0xa0}
var sm2ConstantA = []byte{
0xff, 0xff, 0xff, 0xfe, 0xff, 0xff, 0xff, 0xff,
0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
0xff, 0xff, 0xff, 0xff, 0x00, 0x00, 0x00, 0x00,
0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xfc}
var sm2ConstantB = []byte{
0x28, 0xe9, 0xfa, 0x9e, 0x9d, 0x9f, 0x5e, 0x34,
0x4d, 0x5a, 0x9e, 0x4b, 0xcf, 0x65, 0x09, 0xa7,
0xf3, 0x97, 0x89, 0xf5, 0x15, 0xab, 0x8f, 0x92,
0xdd, 0xbc, 0xbd, 0x41, 0x4d, 0x94, 0x0e, 0x93}
// isLess returns whether a < b, where a and b are big-endian buffers of the
// same length and shorter than 72 bytes.
func isLess(a, b []byte) bool {
if len(a) != len(b) {
panic("ecdh: internal error: mismatched isLess inputs")
}
// Copy the values into a fixed-size preallocated little-endian buffer.
// 72 bytes is enough for every scalar in this package, and having a fixed
// size lets us avoid heap allocations.
if len(a) > 72 {
panic("ecdh: internal error: isLess input too large")
}
bufA, bufB := make([]byte, 72), make([]byte, 72)
for i := range a {
bufA[i], bufB[i] = a[len(a)-i-1], b[len(b)-i-1]
}
// Perform a subtraction with borrow.
var borrow uint64
for i := 0; i < len(bufA); i += 8 {
limbA, limbB := binary.LittleEndian.Uint64(bufA[i:]), binary.LittleEndian.Uint64(bufB[i:])
_, borrow = bits.Sub64(limbA, limbB, borrow)
}
// If there is a borrow at the end of the operation, then a < b.
return borrow == 1
}
var errInvalidPrivateKey = errors.New("ecdh: invalid private key")