/
sm2enc.go
178 lines (149 loc) · 3.83 KB
/
sm2enc.go
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// Copyright 2011 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.
// Package sm2 implements china crypto standards.
package sm2
import (
"bytes"
"crypto"
"encoding/asn1"
"errors"
"github.com/Lcfling/cryptogm/sm3"
"io"
"math"
"math/big"
)
//sm2 enc structure in asn1
type EncData struct {
X *big.Int
Y *big.Int
Hash []byte
C2 []byte
}
var EncryptionErr = errors.New("sm2: encryption error")
var DecryptionErr = errors.New("sm2: decryption error")
func keyDerivation(Z []byte, klen int) []byte {
var ct = 1
if klen%8 != 0 {
return nil
}
K := make([]byte, int(math.Ceil(float64(klen)/(sm3.Size*8))*sm3.Size))
v := sm3.Size * 8
l := int(math.Ceil(float64(klen) / float64(v)))
var m = make([]byte, len(Z)+4)
var vBytes = make([]byte, 4)
copy(m, Z)
for ; ct <= l; ct++ {
vBytes[0] = uint8(ct >> 24)
vBytes[1] = uint8(ct >> 16)
vBytes[2] = uint8(ct >> 8)
vBytes[3] = uint8(ct)
copy(m[len(Z):], vBytes)
hash := sm3.SumSM3(m)
copy(K[(ct-1)*sm3.Size:], hash[:])
}
return K[:klen/8]
}
func Encrypt(rand io.Reader, key *PublicKey, msg []byte) (der []byte, err error) {
x, y, c2, c3, err := doEncrypt(rand, key, msg)
if err != nil {
return nil, err
}
ret := EncData{
X: x,
Y: y,
C2: c2,
Hash: c3,
}
return asn1.Marshal(ret)
}
func doEncrypt(rand io.Reader, key *PublicKey, msg []byte) (x, y *big.Int, c2, c3 []byte, err error) {
k := generateRandK(rand, key.Curve)
regen:
x1, y1 := key.Curve.ScalarBaseMult(k.Bytes())
//c1 := elliptic.Marshal(key.Curve, x1, y1)
//sx,sy := key.Curve.ScalarMult(key.X, key.Y, k.Bytes())
//if sx.Cmp(big.NewInt(0)) == 0 && sy.Cmp(big.NewInt(0)) == 0 {
// return nil, EncryptionErr
//}
x2, y2 := key.Curve.ScalarMult(key.X, key.Y, k.Bytes())
Z := make([]byte, len(x2.Bytes())+len(y2.Bytes()))
copy(Z, x2.Bytes())
copy(Z[len(x2.Bytes()):], y2.Bytes())
t := keyDerivation(Z, len(msg)*8)
if t == nil {
return nil, nil, nil, nil, EncryptionErr
}
for i, v := range t {
if v != 0 {
break
}
if i == len(t)-1 {
goto regen
}
}
//M^t
for i, v := range t {
t[i] = v ^ msg[i]
}
m3 := make([]byte, len(x2.Bytes())+len(y2.Bytes())+len(msg))
copy(m3, x2.Bytes())
copy(m3[len(x2.Bytes()):], msg)
copy(m3[len(x2.Bytes())+len(msg):], y2.Bytes())
c3 = sm3.SumSM3(m3)
//ret := make([]byte, len(c1) + len(t) + len(c3))
//copy(ret, c1)
//copy(ret[len(c1):], c3[:])
//copy(ret[len(c1) + len(c3):], t)
return x1, y1, t, c3, nil
}
func (key *PrivateKey) Decrypt(rand io.Reader, msg []byte, opts crypto.DecrypterOpts) (plaintext []byte, err error) {
return Decrypt(msg, key)
}
func Decrypt(c []byte, key *PrivateKey) ([]byte, error) {
// to do check
//c1Len := 1 + 2*((key.Curve.Params().BitSize + 7) >> 3)
//klen := (len(c) - c1Len - sm3.Size)*8
//x1, y1 := elliptic.Unmarshal(key.Curve, c[:c1Len])
//if x1 == nil {
// return nil, DecryptionErr
//}
sm2enc := new(EncData)
_, err := asn1.Unmarshal(c, sm2enc)
if err != nil {
return nil, errors.New("sm2 decryption error: input do not have correct format")
}
klen := len(sm2enc.C2) * 8
//dB*C1
x2, y2 := key.Curve.ScalarMult(sm2enc.X, sm2enc.Y, key.D.Bytes())
Z := make([]byte, len(x2.Bytes())+len(y2.Bytes()))
copy(Z, x2.Bytes())
copy(Z[len(x2.Bytes()):], y2.Bytes())
t := keyDerivation(Z, klen)
if t == nil {
return nil, EncryptionErr
}
for i, v := range t {
if v != 0 {
break
}
if i == len(t)-1 {
return nil, DecryptionErr
}
}
// m` = c2 ^ t
c2 := c[len(c)-(klen/8):]
for i, v := range t {
t[i] = v ^ c2[i]
}
//validate
_u := make([]byte, len(x2.Bytes())+len(y2.Bytes())+len(t))
copy(_u, x2.Bytes())
copy(_u[len(x2.Bytes()):], t)
copy(_u[len(x2.Bytes())+len(t):], y2.Bytes())
u := sm3.SumSM3(_u)
if !bytes.Equal(u[:], sm2enc.Hash) {
return nil, DecryptionErr
}
return t, nil
}