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key_exchange.go
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key_exchange.go
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package sm9
import (
"io"
"errors"
"math/big"
"crypto/subtle"
"github.com/deatil/go-cryptobin/hash/sm3"
"github.com/deatil/go-cryptobin/kdf/smkdf"
"github.com/deatil/go-cryptobin/gm/sm9/sm9curve"
)
// KeyExchange represents key exchange struct, include internal stat in whole key exchange flow.
// Initiator's flow will be: NewKeyExchange -> InitKeyExchange -> transmission -> ConfirmResponder
// Responder's flow will be: NewKeyExchange -> waiting ... -> RepondKeyExchange -> transmission -> ConfirmInitiator
type KeyExchange struct {
genSignature bool // control the optional sign/verify step triggered by responsder
keyLength int // key length
privateKey *EncryptPrivateKey // owner's encryption private key
uid []byte // owner uid
peerUID []byte // peer uid
r *big.Int // random which will be used to compute secret
secret *sm9curve.G1 // generated secret which will be passed to peer
peerSecret *sm9curve.G1 // received peer's secret
g1 *sm9curve.GT // internal state which will be used when compute the key and signature
g2 *sm9curve.GT // internal state which will be used when compute the key and signature
g3 *sm9curve.GT // internal state which will be used when compute the key and signature
}
// NewKeyExchange creates one new KeyExchange object
func NewKeyExchange(priv *EncryptPrivateKey, uid, peerUID []byte, keyLen int, genSignature bool) *KeyExchange {
ke := &KeyExchange{}
ke.genSignature = genSignature
ke.keyLength = keyLen
ke.privateKey = priv
ke.uid = uid
ke.peerUID = peerUID
return ke
}
// Reset clears all internal state and Ephemeral private/public keys
func (ke *KeyExchange) Reset() {
if ke.r != nil {
ke.r.SetBytes([]byte{0})
}
if ke.g1 != nil {
ke.g1.SetOne()
}
if ke.g2 != nil {
ke.g2.SetOne()
}
if ke.g3 != nil {
ke.g3.SetOne()
}
}
func (ke *KeyExchange) initKeyExchange(hid byte, r *big.Int) error {
pubB, err := ke.privateKey.GenerateUserPublicKey(ke.peerUID, hid)
if err != nil {
return err
}
ke.r = r
rA, err := new(sm9curve.G1).ScalarMult(pubB, sm9curve.NormalizeScalar(ke.r.Bytes()))
if err != nil {
return err
}
ke.secret = rA
return nil
}
// InitKeyExchange generates random with responder uid, for initiator's step A1-A4
func (ke *KeyExchange) InitKeyExchange(rand io.Reader, hid byte) (*sm9curve.G1, error) {
r, err := randFieldElement(rand, sm9curve.Order)
if err != nil {
return nil, err
}
err = ke.initKeyExchange(hid, r)
if err != nil {
return nil, err
}
return ke.secret, nil
}
func (ke *KeyExchange) sign(isResponder bool, prefix byte) []byte {
var buffer []byte
hash := sm3.New()
hash.Write(ke.g2.Marshal())
hash.Write(ke.g3.Marshal())
if isResponder {
hash.Write(ke.peerUID)
hash.Write(ke.uid)
hash.Write(ke.peerSecret.Marshal())
hash.Write(ke.secret.Marshal())
} else {
hash.Write(ke.uid)
hash.Write(ke.peerUID)
hash.Write(ke.secret.Marshal())
hash.Write(ke.peerSecret.Marshal())
}
buffer = hash.Sum(nil)
hash.Reset()
hash.Write([]byte{prefix})
hash.Write(ke.g1.Marshal())
hash.Write(buffer)
return hash.Sum(nil)
}
func (ke *KeyExchange) generateSharedKey(isResponder bool) ([]byte, error) {
var buffer []byte
if isResponder {
buffer = append(buffer, ke.peerUID...)
buffer = append(buffer, ke.uid...)
buffer = append(buffer, ke.peerSecret.Marshal()...)
buffer = append(buffer, ke.secret.Marshal()...)
} else {
buffer = append(buffer, ke.uid...)
buffer = append(buffer, ke.peerUID...)
buffer = append(buffer, ke.secret.Marshal()...)
buffer = append(buffer, ke.peerSecret.Marshal()...)
}
buffer = append(buffer, ke.g1.Marshal()...)
buffer = append(buffer, ke.g2.Marshal()...)
buffer = append(buffer, ke.g3.Marshal()...)
return smkdf.Key(sm3.New, buffer, ke.keyLength), nil
}
func (ke *KeyExchange) respondKeyExchange(hid byte, r *big.Int, rA *sm9curve.G1) (*sm9curve.G1, []byte, error) {
if !rA.IsOnCurve() {
return nil, nil, errors.New("sm9: invalid initiator's ephemeral public key")
}
ke.peerSecret = rA
pubA, err := ke.privateKey.GenerateUserPublicKey(ke.peerUID, hid)
if err != nil {
return nil, nil, err
}
ke.r = r
rBytes := sm9curve.NormalizeScalar(r.Bytes())
rB, err := new(sm9curve.G1).ScalarMult(pubA, rBytes)
if err != nil {
return nil, nil, err
}
ke.secret = rB
ke.g1 = sm9curve.Pair(ke.peerSecret, ke.privateKey.Sk)
g3, err := sm9curve.ScalarMultGT(ke.g1, rBytes)
if err != nil {
return nil, nil, err
}
ke.g3 = g3
g2Pair := sm9curve.Pair(ke.privateKey.Mpk, sm9curve.Gen2)
g2, err := sm9curve.ScalarMultGT(g2Pair, rBytes)
if err != nil {
return nil, nil, err
}
ke.g2 = g2
if !ke.genSignature {
return ke.secret, nil, nil
}
return ke.secret, ke.sign(true, 0x82), nil
}
// RepondKeyExchange when responder receive rA, for responder's step B1-B7
func (ke *KeyExchange) RepondKeyExchange(rand io.Reader, hid byte, rA *sm9curve.G1) (*sm9curve.G1, []byte, error) {
r, err := randFieldElement(rand, sm9curve.Order)
if err != nil {
return nil, nil, err
}
return ke.respondKeyExchange(hid, r, rA)
}
// ConfirmResponder for initiator's step A5-A7
func (ke *KeyExchange) ConfirmResponder(rB *sm9curve.G1, sB []byte) ([]byte, []byte, error) {
if !rB.IsOnCurve() {
return nil, nil, errors.New("sm9: invalid responder's ephemeral public key")
}
// step 5
ke.peerSecret = rB
g1Pair := sm9curve.Pair(ke.privateKey.Mpk, sm9curve.Gen2)
g1, err := sm9curve.ScalarMultGT(g1Pair, sm9curve.NormalizeScalar(ke.r.Bytes()))
if err != nil {
return nil, nil, err
}
ke.g1 = g1
ke.g2 = sm9curve.Pair(ke.peerSecret, ke.privateKey.Sk)
g3, err := sm9curve.ScalarMultGT(ke.g2, sm9curve.NormalizeScalar(ke.r.Bytes()))
if err != nil {
return nil, nil, err
}
ke.g3 = g3
// step 6, verify signature
if len(sB) > 0 {
signature := ke.sign(false, 0x82)
if subtle.ConstantTimeCompare(signature, sB) != 1 {
return nil, nil, errors.New("sm9: invalid responder's signature")
}
}
key, err := ke.generateSharedKey(false)
if err != nil {
return nil, nil, err
}
if !ke.genSignature {
return key, nil, nil
}
return key, ke.sign(false, 0x83), nil
}
// ConfirmInitiator for responder's step B8
func (ke *KeyExchange) ConfirmInitiator(s1 []byte) ([]byte, error) {
if s1 != nil {
buffer := ke.sign(true, 0x83)
if subtle.ConstantTimeCompare(buffer, s1) != 1 {
return nil, errors.New("sm9: invalid initiator's signature")
}
}
return ke.generateSharedKey(true)
}