mirror of
https://github.com/emmansun/gmsm.git
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417 lines
12 KiB
Go
417 lines
12 KiB
Go
package sm2
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import (
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"crypto/ecdsa"
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"crypto/elliptic"
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_subtle "crypto/subtle"
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"errors"
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"fmt"
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"io"
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"math/big"
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"strings"
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"github.com/emmansun/gmsm/internal/subtle"
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"github.com/emmansun/gmsm/sm2/sm2ec"
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"github.com/emmansun/gmsm/sm3"
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"golang.org/x/crypto/cryptobyte"
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"golang.org/x/crypto/cryptobyte/asn1"
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)
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// This file contains a math/big implementation of SM2 DSA/Encryption that is only used for
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// deprecated custom curves.
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// A invertible implements fast inverse in GF(N).
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type invertible interface {
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// Inverse returns the inverse of k mod Params().N.
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Inverse(k *big.Int) *big.Int
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}
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// A combinedMult implements fast combined multiplication for verification.
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type combinedMult interface {
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// CombinedMult returns [s1]G + [s2]P where G is the generator.
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CombinedMult(bigX, bigY *big.Int, baseScalar, scalar []byte) (x, y *big.Int)
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}
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// hashToInt converts a hash value to an integer. Per FIPS 186-4, Section 6.4,
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// we use the left-most bits of the hash to match the bit-length of the order of
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// the curve. This also performs Step 5 of SEC 1, Version 2.0, Section 4.1.3.
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func hashToInt(hash []byte, c elliptic.Curve) *big.Int {
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orderBits := c.Params().N.BitLen()
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orderBytes := (orderBits + 7) / 8
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if len(hash) > orderBytes {
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hash = hash[:orderBytes]
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}
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ret := new(big.Int).SetBytes(hash)
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excess := len(hash)*8 - orderBits
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if excess > 0 {
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ret.Rsh(ret, uint(excess))
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}
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return ret
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}
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var errZeroParam = errors.New("zero parameter")
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// Sign signs a hash (which should be the result of hashing a larger message)
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// using the private key, priv. If the hash is longer than the bit-length of the
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// private key's curve order, the hash will be truncated to that length. It
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// returns the signature as a pair of integers. Most applications should use
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// SignASN1 instead of dealing directly with r, s.
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//
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// Compliance with GB/T 32918.2-2016 regardless it's SM2 curve or not.
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func Sign(rand io.Reader, priv *ecdsa.PrivateKey, hash []byte) (r, s *big.Int, err error) {
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key := new(PrivateKey)
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key.PrivateKey = *priv
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sig, err := SignASN1(rand, key, hash, nil)
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if err != nil {
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return nil, nil, err
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}
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r, s = new(big.Int), new(big.Int)
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var inner cryptobyte.String
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input := cryptobyte.String(sig)
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if !input.ReadASN1(&inner, asn1.SEQUENCE) ||
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!input.Empty() ||
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!inner.ReadASN1Integer(r) ||
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!inner.ReadASN1Integer(s) ||
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!inner.Empty() {
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return nil, nil, errors.New("invalid ASN.1 from SignASN1")
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}
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return r, s, nil
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}
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func signLegacy(priv *PrivateKey, rand io.Reader, hash []byte) (sig []byte, err error) {
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// See [NSA] 3.4.1
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c := priv.PublicKey.Curve
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N := c.Params().N
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if N.Sign() == 0 {
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return nil, errZeroParam
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}
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var k, r, s *big.Int
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e := hashToInt(hash, c)
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for {
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for {
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k, err = randFieldElement(c, rand)
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if err != nil {
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return nil, err
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}
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r, _ = priv.Curve.ScalarBaseMult(k.Bytes()) // (x, y) = k*G
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r.Add(r, e) // r = x + e
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r.Mod(r, N) // r = (x + e) mod N
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if r.Sign() != 0 {
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t := new(big.Int).Add(r, k)
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if t.Cmp(N) != 0 { // if r != 0 && (r + k) != N then ok
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break
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}
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}
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}
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s = new(big.Int).Mul(priv.D, r)
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s = new(big.Int).Sub(k, s)
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dp1 := new(big.Int).Add(priv.D, one)
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var dp1Inv *big.Int
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if in, ok := priv.Curve.(invertible); ok {
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dp1Inv = in.Inverse(dp1)
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} else {
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dp1Inv = fermatInverse(dp1, N) // N != 0
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}
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s.Mul(s, dp1Inv)
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s.Mod(s, N) // N != 0
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if s.Sign() != 0 {
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break
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}
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}
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return encodeSignature(r.Bytes(), s.Bytes())
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}
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// fermatInverse calculates the inverse of k in GF(P) using Fermat's method
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// (exponentiation modulo P - 2, per Euler's theorem). This has better
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// constant-time properties than Euclid's method (implemented in
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// math/big.Int.ModInverse and FIPS 186-4, Appendix C.1) although math/big
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// itself isn't strictly constant-time so it's not perfect.
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func fermatInverse(k, N *big.Int) *big.Int {
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two := big.NewInt(2)
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nMinus2 := new(big.Int).Sub(N, two)
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return new(big.Int).Exp(k, nMinus2, N)
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}
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// SignWithSM2 follow sm2 dsa standards for hash part, compliance with GB/T 32918.2-2016.
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func SignWithSM2(rand io.Reader, priv *ecdsa.PrivateKey, uid, msg []byte) (r, s *big.Int, err error) {
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digest, err := CalculateSM2Hash(&priv.PublicKey, msg, uid)
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if err != nil {
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return nil, nil, err
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}
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return Sign(rand, priv, digest)
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}
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// Verify verifies the signature in r, s of hash using the public key, pub. Its
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// return value records whether the signature is valid. Most applications should
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// use VerifyASN1 instead of dealing directly with r, s.
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//
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// Compliance with GB/T 32918.2-2016 regardless it's SM2 curve or not.
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// Caller should make sure the hash's correctness.
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func Verify(pub *ecdsa.PublicKey, hash []byte, r, s *big.Int) bool {
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if r.Sign() <= 0 || s.Sign() <= 0 {
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return false
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}
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sig, err := encodeSignature(r.Bytes(), s.Bytes())
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if err != nil {
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return false
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}
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return VerifyASN1(pub, hash, sig)
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}
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func verifyLegacy(pub *ecdsa.PublicKey, hash, sig []byte) bool {
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rBytes, sBytes, err := parseSignature(sig)
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if err != nil {
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return false
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}
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r, s := new(big.Int).SetBytes(rBytes), new(big.Int).SetBytes(sBytes)
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c := pub.Curve
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N := c.Params().N
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if r.Sign() <= 0 || s.Sign() <= 0 {
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return false
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}
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if r.Cmp(N) >= 0 || s.Cmp(N) >= 0 {
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return false
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}
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e := hashToInt(hash, c)
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t := new(big.Int).Add(r, s)
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t.Mod(t, N)
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if t.Sign() == 0 {
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return false
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}
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var x *big.Int
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if opt, ok := c.(combinedMult); ok {
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x, _ = opt.CombinedMult(pub.X, pub.Y, s.Bytes(), t.Bytes())
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} else {
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x1, y1 := c.ScalarBaseMult(s.Bytes())
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x2, y2 := c.ScalarMult(pub.X, pub.Y, t.Bytes())
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x, _ = c.Add(x1, y1, x2, y2)
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}
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x.Add(x, e)
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x.Mod(x, N)
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return x.Cmp(r) == 0
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}
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// VerifyWithSM2 verifies the signature in r, s of raw msg and uid using the public key, pub.
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// It returns value records whether the signature is valid. Compliance with GB/T 32918.2-2016.
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func VerifyWithSM2(pub *ecdsa.PublicKey, uid, msg []byte, r, s *big.Int) bool {
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digest, err := CalculateSM2Hash(pub, msg, uid)
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if err != nil {
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return false
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}
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return Verify(pub, digest, r, s)
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}
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var (
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one = new(big.Int).SetInt64(1)
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)
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// randFieldElement returns a random element of the order of the given
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// curve using the procedure given in FIPS 186-4, Appendix B.5.2.
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func randFieldElement(c elliptic.Curve, rand io.Reader) (k *big.Int, err error) {
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// See randomPoint for notes on the algorithm. This has to match, or s390x
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// signatures will come out different from other architectures, which will
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// break TLS recorded tests.
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for {
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N := c.Params().N
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b := make([]byte, (N.BitLen()+7)/8)
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if _, err = io.ReadFull(rand, b); err != nil {
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return
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}
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if excess := len(b)*8 - N.BitLen(); excess > 0 {
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b[0] >>= excess
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}
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k = new(big.Int).SetBytes(b)
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if k.Sign() != 0 && k.Cmp(N) < 0 {
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return
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}
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}
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}
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func encryptLegacy(random io.Reader, pub *ecdsa.PublicKey, msg []byte, opts *EncrypterOpts) ([]byte, error) {
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curve := pub.Curve
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msgLen := len(msg)
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var retryCount int = 0
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for {
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//A1, generate random k
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k, err := randFieldElement(curve, random)
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if err != nil {
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return nil, err
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}
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//A2, calculate C1 = k * G
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x1, y1 := curve.ScalarBaseMult(k.Bytes())
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c1 := opts.pointMarshalMode.mashal(curve, x1, y1)
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//A4, calculate k * P (point of Public Key)
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x2, y2 := curve.ScalarMult(pub.X, pub.Y, k.Bytes())
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//A5, calculate t=KDF(x2||y2, klen)
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c2 := sm3.Kdf(append(bigIntToBytes(curve, x2), bigIntToBytes(curve, y2)...), msgLen)
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if subtle.ConstantTimeAllZero(c2) == 1 {
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retryCount++
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if retryCount > maxRetryLimit {
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return nil, fmt.Errorf("sm2: A5, failed to calculate valid t, tried %v times", retryCount)
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}
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continue
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}
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//A6, C2 = M + t;
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subtle.XORBytes(c2, msg, c2)
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//A7, C3 = hash(x2||M||y2)
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c3 := calculateC3(curve, x2, y2, msg)
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if opts.ciphertextEncoding == ENCODING_PLAIN {
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if opts.ciphertextSplicingOrder == C1C3C2 {
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// c1 || c3 || c2
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return append(append(c1, c3...), c2...), nil
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}
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// c1 || c2 || c3
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return append(append(c1, c2...), c3...), nil
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}
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// ASN.1 format will force C3 C2 order
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return mashalASN1Ciphertext(x1, y1, c2, c3)
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}
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}
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func calculateC3(curve elliptic.Curve, x2, y2 *big.Int, msg []byte) []byte {
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md := sm3.New()
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md.Write(bigIntToBytes(curve, x2))
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md.Write(msg)
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md.Write(bigIntToBytes(curve, y2))
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return md.Sum(nil)
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}
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func mashalASN1Ciphertext(x1, y1 *big.Int, c2, c3 []byte) ([]byte, error) {
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var b cryptobyte.Builder
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b.AddASN1(asn1.SEQUENCE, func(b *cryptobyte.Builder) {
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b.AddASN1BigInt(x1)
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b.AddASN1BigInt(y1)
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b.AddASN1OctetString(c3)
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b.AddASN1OctetString(c2)
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})
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return b.Bytes()
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}
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func decryptASN1(priv *PrivateKey, ciphertext []byte) ([]byte, error) {
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x1, y1, c2, c3, err := unmarshalASN1Ciphertext(ciphertext)
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if err != nil {
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return nil, ErrDecryption
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}
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return rawDecrypt(priv, x1, y1, c2, c3)
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}
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func rawDecrypt(priv *PrivateKey, x1, y1 *big.Int, c2, c3 []byte) ([]byte, error) {
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curve := priv.Curve
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x2, y2 := curve.ScalarMult(x1, y1, priv.D.Bytes())
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msgLen := len(c2)
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msg := sm3.Kdf(append(bigIntToBytes(curve, x2), bigIntToBytes(curve, y2)...), msgLen)
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if subtle.ConstantTimeAllZero(c2) == 1 {
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return nil, ErrDecryption
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}
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//B5, calculate msg = c2 ^ t
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subtle.XORBytes(msg, c2, msg)
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u := calculateC3(curve, x2, y2, msg)
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if _subtle.ConstantTimeCompare(u, c3) == 1 {
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return msg, nil
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}
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return nil, ErrDecryption
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}
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func decryptLegacy(priv *PrivateKey, ciphertext []byte, opts *DecrypterOpts) ([]byte, error) {
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splicingOrder := C1C3C2
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if opts != nil {
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if opts.ciphertextEncoding == ENCODING_ASN1 {
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return decryptASN1(priv, ciphertext)
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}
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splicingOrder = opts.ciphertextSplicingOrder
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}
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if ciphertext[0] == 0x30 {
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return decryptASN1(priv, ciphertext)
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}
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ciphertextLen := len(ciphertext)
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curve := priv.Curve
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// B1, get C1, and check C1
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x1, y1, c3Start, err := bytesToPoint(curve, ciphertext)
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if err != nil {
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return nil, ErrDecryption
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}
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//B4, calculate t=KDF(x2||y2, klen)
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var c2, c3 []byte
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if splicingOrder == C1C3C2 {
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c2 = ciphertext[c3Start+sm3.Size:]
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c3 = ciphertext[c3Start : c3Start+sm3.Size]
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} else {
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c2 = ciphertext[c3Start : ciphertextLen-sm3.Size]
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c3 = ciphertext[ciphertextLen-sm3.Size:]
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}
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return rawDecrypt(priv, x1, y1, c2, c3)
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}
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func (mode pointMarshalMode) mashal(curve elliptic.Curve, x, y *big.Int) []byte {
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switch mode {
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case MarshalCompressed:
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return elliptic.MarshalCompressed(curve, x, y)
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case MarshalHybrid:
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buffer := elliptic.Marshal(curve, x, y)
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buffer[0] = byte(y.Bit(0)) | hybrid06
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return buffer
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default:
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return elliptic.Marshal(curve, x, y)
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}
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}
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func bytesToPoint(curve elliptic.Curve, bytes []byte) (*big.Int, *big.Int, int, error) {
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if len(bytes) < 1+(curve.Params().BitSize/8) {
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return nil, nil, 0, fmt.Errorf("sm2: invalid bytes length %d", len(bytes))
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}
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format := bytes[0]
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byteLen := (curve.Params().BitSize + 7) >> 3
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switch format {
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case uncompressed, hybrid06, hybrid07: // what's the hybrid format purpose?
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if len(bytes) < 1+byteLen*2 {
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return nil, nil, 0, fmt.Errorf("sm2: invalid point uncompressed/hybrid form bytes length %d", len(bytes))
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}
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data := make([]byte, 1+byteLen*2)
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data[0] = uncompressed
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copy(data[1:], bytes[1:1+byteLen*2])
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x, y := sm2ec.Unmarshal(curve, data)
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if x == nil || y == nil {
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return nil, nil, 0, fmt.Errorf("sm2: point is not on curve %s", curve.Params().Name)
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}
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return x, y, 1 + byteLen*2, nil
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case compressed02, compressed03:
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if len(bytes) < 1+byteLen {
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return nil, nil, 0, fmt.Errorf("sm2: invalid point compressed form bytes length %d", len(bytes))
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}
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// Make sure it's NIST curve or SM2 P-256 curve
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if strings.HasPrefix(curve.Params().Name, "P-") || strings.EqualFold(curve.Params().Name, sm2ec.P256().Params().Name) {
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// y² = x³ - 3x + b, prime curves
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x, y := sm2ec.UnmarshalCompressed(curve, bytes[:1+byteLen])
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if x == nil || y == nil {
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return nil, nil, 0, fmt.Errorf("sm2: point is not on curve %s", curve.Params().Name)
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}
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return x, y, 1 + byteLen, nil
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}
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return nil, nil, 0, fmt.Errorf("sm2: unsupported point form %d, curve %s", format, curve.Params().Name)
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}
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return nil, nil, 0, fmt.Errorf("sm2: unknown point form %d", format)
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}
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