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SM2: key exchange
This commit is contained in:
Sun Yimin
GitHub
parent
21b8f82a6e
commit
23914a86c3
255
sm2/sm2_keyexchange.go
Normal file
255
sm2/sm2_keyexchange.go
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@ -0,0 +1,255 @@
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package sm2
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import (
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"crypto/ecdsa"
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goSubtle "crypto/subtle"
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"errors"
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"io"
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"math/big"
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"github.com/emmansun/gmsm/sm3"
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)
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// Point represent point on curve
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type Point struct {
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X *big.Int
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Y *big.Int
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}
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// KeyExchange key exchange struct, include internal stat in whole key exchange flow.
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// Initiator's flow will be: NewKeyExchange -> InitKeyExchange -> transmission -> ConfirmResponder
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// Responder's flow will be: NewKeyExchange -> waiting ... -> RepondKeyExchange -> transmission -> ConfirmInitiator
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type KeyExchange struct {
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genSignature bool // control the optional sign/verify step triggered by responsder
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keyLength int // key length
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privateKey *PrivateKey // owner's encryption private key
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uid []byte // owner uid
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peerUID []byte // peer uid
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peerPub *ecdsa.PublicKey // peer public key
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r *big.Int // random which will be used to compute secret
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secret Point // generated secret which will be passed to peer
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peerSecret Point // received peer's secret
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w2 *big.Int // internal state which will be used when compute the key and signature
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w2Minus1 *big.Int // internal state which will be used when compute the key and signature
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v Point // internal state which will be used when compute the key and signature
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key []byte // key will be used after key agreement
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}
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// GetKey return key after key agreement
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func (ke *KeyExchange) GetKey() []byte {
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return ke.key
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}
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// NewKeyExchange create one new KeyExchange object
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func NewKeyExchange(priv *PrivateKey, peerPub *ecdsa.PublicKey, uid, peerUID []byte, keyLen int, genSignature bool) *KeyExchange {
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ke := &KeyExchange{}
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ke.genSignature = genSignature
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ke.peerPub = peerPub
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ke.keyLength = keyLen
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ke.privateKey = priv
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ke.uid = uid
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ke.peerUID = peerUID
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w := (priv.Params().N.BitLen()+1)/2 - 1
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x2 := big.NewInt(2)
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ke.w2 = x2
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x2.Lsh(x2, uint(w))
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x2minus1 := (&big.Int{}).Sub(x2, big.NewInt(1))
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ke.w2Minus1 = x2minus1
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return ke
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}
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func initKeyExchange(ke *KeyExchange, r *big.Int) {
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ke.secret.X, ke.secret.Y = ke.privateKey.ScalarBaseMult(r.Bytes())
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ke.r = r
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}
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// InitKeyExchange generate random with responder uid, for initiator's step A1-A3
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func (ke *KeyExchange) InitKeyExchange(rand io.Reader) (*Point, error) {
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r, err := randFieldElement(ke.privateKey, rand)
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if err != nil {
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return nil, err
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}
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initKeyExchange(ke, r)
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return &ke.secret, nil
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}
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func respondKeyExchange(ke *KeyExchange, r *big.Int, rA *Point) (*Point, []byte, error) {
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ke.secret.X, ke.secret.Y = ke.privateKey.ScalarBaseMult(r.Bytes())
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ke.r = r
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t := (&big.Int{}).And(ke.w2Minus1, ke.secret.X)
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t.Add(ke.w2, t)
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t.Mul(t, ke.r)
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t.Add(t, ke.privateKey.D)
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t.Mod(t, ke.privateKey.Params().N)
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x1 := (&big.Int{}).And(ke.w2Minus1, ke.peerSecret.X)
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x1.Add(ke.w2, x1)
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x3, y3 := ke.privateKey.ScalarMult(ke.peerSecret.X, ke.peerSecret.Y, x1.Bytes())
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x3, y3 = ke.privateKey.Add(ke.peerPub.X, ke.peerPub.Y, x3, y3)
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ke.v.X, ke.v.Y = ke.privateKey.ScalarMult(x3, y3, t.Bytes())
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if ke.v.X.Sign() == 0 && ke.v.Y.Sign() == 0 {
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return nil, nil, errors.New("sm2: key exchange fail")
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}
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var buffer []byte
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zA, err := calculateZA(ke.peerPub, ke.peerUID)
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if err != nil {
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return nil, nil, err
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}
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zB, err := calculateZA(&ke.privateKey.PublicKey, ke.uid)
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if err != nil {
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return nil, nil, err
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}
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buffer = append(buffer, toBytes(ke.privateKey, ke.v.X)...)
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buffer = append(buffer, toBytes(ke.privateKey, ke.v.Y)...)
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buffer = append(buffer, zA...)
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buffer = append(buffer, zB...)
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key, _ := sm3.Kdf(buffer, ke.keyLength)
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ke.key = key
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if !ke.genSignature {
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return &ke.secret, nil, nil
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}
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hash := sm3.New()
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hash.Write(toBytes(ke.privateKey, ke.v.X))
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hash.Write(zA)
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hash.Write(zB)
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hash.Write(toBytes(ke.privateKey, ke.peerSecret.X))
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hash.Write(toBytes(ke.privateKey, ke.peerSecret.Y))
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hash.Write(toBytes(ke.privateKey, ke.secret.X))
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hash.Write(toBytes(ke.privateKey, ke.secret.Y))
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buffer = hash.Sum(nil)
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hash.Reset()
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hash.Write([]byte{0x02})
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hash.Write(toBytes(ke.privateKey, ke.v.Y))
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hash.Write(buffer)
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buffer = hash.Sum(nil)
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return &ke.secret, buffer, nil
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}
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// RepondKeyExchange when responder receive rA, for responder's step B1-B8
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func (ke *KeyExchange) RepondKeyExchange(rand io.Reader, rA *Point) (*Point, []byte, error) {
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if !ke.privateKey.IsOnCurve(rA.X, rA.Y) {
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return nil, nil, errors.New("sm2: received invalid random from initiator")
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}
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ke.peerSecret = *rA
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r, err := randFieldElement(ke.privateKey, rand)
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if err != nil {
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return nil, nil, err
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}
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return respondKeyExchange(ke, r, rA)
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}
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// ConfirmResponder for initiator's step A4-A10
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func (ke *KeyExchange) ConfirmResponder(rB *Point, sB []byte) ([]byte, error) {
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if !ke.privateKey.IsOnCurve(rB.X, rB.Y) {
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return nil, errors.New("sm2: received invalid random from responder")
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}
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hash := sm3.New()
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ke.peerSecret = *rB
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t := (&big.Int{}).And(ke.w2Minus1, ke.secret.X)
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t.Add(ke.w2, t)
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t.Mul(t, ke.r)
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t.Add(t, ke.privateKey.D)
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t.Mod(t, ke.privateKey.Params().N)
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x2 := (&big.Int{}).And(ke.w2Minus1, ke.peerSecret.X)
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x2.Add(ke.w2, x2)
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x3, y3 := ke.privateKey.ScalarMult(ke.peerSecret.X, ke.peerSecret.Y, x2.Bytes())
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x3, y3 = ke.privateKey.Add(ke.peerPub.X, ke.peerPub.Y, x3, y3)
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ke.v.X, ke.v.Y = ke.privateKey.ScalarMult(x3, y3, t.Bytes())
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if ke.v.X.Sign() == 0 && ke.v.Y.Sign() == 0 {
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return nil, errors.New("sm2: key exchange fail")
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}
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var buffer []byte
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zA, err := calculateZA(&ke.privateKey.PublicKey, ke.uid)
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if err != nil {
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return nil, err
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}
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zB, err := calculateZA(ke.peerPub, ke.peerUID)
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if err != nil {
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return nil, err
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}
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buffer = append(buffer, toBytes(ke.privateKey, ke.v.X)...)
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buffer = append(buffer, toBytes(ke.privateKey, ke.v.Y)...)
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buffer = append(buffer, zA...)
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buffer = append(buffer, zB...)
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key, _ := sm3.Kdf(buffer, ke.keyLength)
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ke.key = key
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if len(sB) > 0 {
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hash.Write(toBytes(ke.privateKey, ke.v.X))
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hash.Write(zA)
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hash.Write(zB)
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hash.Write(toBytes(ke.privateKey, ke.secret.X))
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hash.Write(toBytes(ke.privateKey, ke.secret.Y))
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hash.Write(toBytes(ke.privateKey, ke.peerSecret.X))
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hash.Write(toBytes(ke.privateKey, ke.peerSecret.Y))
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buffer = hash.Sum(nil)
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hash.Reset()
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hash.Write([]byte{0x02})
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hash.Write(toBytes(ke.privateKey, ke.v.Y))
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hash.Write(buffer)
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buffer = hash.Sum(nil)
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hash.Reset()
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if goSubtle.ConstantTimeCompare(buffer, sB) != 1 {
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return nil, errors.New("sm2: verify responder's signature fail")
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}
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}
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hash.Write(toBytes(ke.privateKey, ke.v.X))
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hash.Write(zA)
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hash.Write(zB)
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hash.Write(toBytes(ke.privateKey, ke.secret.X))
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hash.Write(toBytes(ke.privateKey, ke.secret.Y))
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hash.Write(toBytes(ke.privateKey, ke.peerSecret.X))
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hash.Write(toBytes(ke.privateKey, ke.peerSecret.Y))
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buffer = hash.Sum(nil)
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hash.Reset()
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hash.Write([]byte{0x03})
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hash.Write(toBytes(ke.privateKey, ke.v.Y))
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hash.Write(buffer)
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buffer = hash.Sum(nil)
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return buffer, nil
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}
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// ConfirmInitiator for responder's step B10
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func (ke *KeyExchange) ConfirmInitiator(s1 []byte) error {
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hash := sm3.New()
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var buffer []byte
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zB, err := calculateZA(&ke.privateKey.PublicKey, ke.uid)
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if err != nil {
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return err
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}
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zA, err := calculateZA(ke.peerPub, ke.peerUID)
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if err != nil {
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return err
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}
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hash.Write(toBytes(ke.privateKey, ke.v.X))
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hash.Write(zA)
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hash.Write(zB)
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hash.Write(toBytes(ke.privateKey, ke.peerSecret.X))
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hash.Write(toBytes(ke.privateKey, ke.peerSecret.Y))
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hash.Write(toBytes(ke.privateKey, ke.secret.X))
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hash.Write(toBytes(ke.privateKey, ke.secret.Y))
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buffer = hash.Sum(nil)
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hash.Reset()
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hash.Write([]byte{0x03})
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hash.Write(toBytes(ke.privateKey, ke.v.Y))
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hash.Write(buffer)
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buffer = hash.Sum(nil)
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if goSubtle.ConstantTimeCompare(buffer, s1) != 1 {
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return errors.New("sm2: verify initiator's signature fail")
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}
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return nil
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}
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38
sm2/sm2_keyexchange_test.go
Normal file
38
sm2/sm2_keyexchange_test.go
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@ -0,0 +1,38 @@
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package sm2
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import (
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"crypto/rand"
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"encoding/hex"
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"testing"
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)
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func TestKeyExchangeSample(t *testing.T) {
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priv1, _ := GenerateKey(rand.Reader)
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priv2, _ := GenerateKey(rand.Reader)
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initiator := NewKeyExchange(priv1, &priv2.PublicKey, []byte("Alice"), []byte("Bob"), 32, true)
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responsder := NewKeyExchange(priv2, &priv1.PublicKey, []byte("Bob"), []byte("Alice"), 32, true)
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rA, err := initiator.InitKeyExchange(rand.Reader)
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if err != nil {
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t.Fatal(err)
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}
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rB, s2, err := responsder.RepondKeyExchange(rand.Reader, rA)
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if err != nil {
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t.Fatal(err)
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}
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s1, err := initiator.ConfirmResponder(rB, s2)
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if err != nil {
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t.Fatal(err)
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}
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err = responsder.ConfirmInitiator(s1)
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if err != nil {
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t.Fatal(err)
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}
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if hex.EncodeToString(initiator.key) != hex.EncodeToString(responsder.key) {
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t.Errorf("got different key")
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}
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}
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@ -549,7 +549,7 @@ func (ke *KeyExchange) InitKeyExchange(rand io.Reader, hid byte) (*bn256.G1, err
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func respondKeyExchange(ke *KeyExchange, hid byte, r *big.Int, rA *bn256.G1) (*bn256.G1, []byte, error) {
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if !rA.IsOnCurve() {
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return nil, nil, errors.New("SM9: received invalid random from initiator")
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return nil, nil, errors.New("sm9: received invalid random from initiator")
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}
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ke.peerSecret = rA
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pubA := ke.privateKey.GenerateUserPublicKey(ke.peerUID, hid)
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@ -605,6 +605,9 @@ func (ke *KeyExchange) RepondKeyExchange(rand io.Reader, hid byte, rA *bn256.G1)
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// ConfirmResponder for initiator's step A5-A7
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func (ke *KeyExchange) ConfirmResponder(rB *bn256.G1, sB []byte) ([]byte, error) {
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if !rB.IsOnCurve() {
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return nil, errors.New("sm9: received invalid random from responder")
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}
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hash := sm3.New()
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// step 5
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ke.peerSecret = rB
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@ -630,7 +633,7 @@ func (ke *KeyExchange) ConfirmResponder(rB *bn256.G1, sB []byte) ([]byte, error)
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signature := hash.Sum(nil)
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hash.Reset()
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if goSubtle.ConstantTimeCompare(signature, sB) != 1 {
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return nil, errors.New("sm9: verify signature fail")
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return nil, errors.New("sm9: verify responder's signature fail")
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}
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}
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buffer = append(buffer, ke.uid...)
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@ -668,7 +671,7 @@ func (ke *KeyExchange) ConfirmInitiator(s1 []byte) error {
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hash.Write(buffer)
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buffer = hash.Sum(nil)
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if goSubtle.ConstantTimeCompare(buffer, s1) != 1 {
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return errors.New("sm9: verify signature fail")
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return errors.New("sm9: verify initiator's signature fail")
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}
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return nil
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}
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