func (ka *ecdheKeyAgreement) processClientKeyExchange(config *Config, cert *Certificate, ckx *clientKeyExchangeMsg, version uint16) ([]byte, error) {
if len(ckx.ciphertext) == 0 || int(ckx.ciphertext[0]) != len(ckx.ciphertext)-1 {
return nil, errClientKeyExchange
}
if ka.curveid == X25519 {
if len(ckx.ciphertext) != 1+32 {
return nil, errClientKeyExchange
}
var theirPublic, sharedKey, scalar [32]byte
copy(theirPublic[:], ckx.ciphertext[1:])
copy(scalar[:], ka.privateKey)
curve25519.ScalarMult(&sharedKey, &scalar, &theirPublic)
return sharedKey[:], nil
}
curve, ok := curveForCurveID(ka.curveid)
if !ok {
panic("internal error")
}
x, y := elliptic.Unmarshal(curve, ckx.ciphertext[1:])
if x == nil {
return nil, errClientKeyExchange
}
if !curve.IsOnCurve(x, y) {
return nil, errClientKeyExchange
}
x, _ = curve.ScalarMult(x, y, ka.privateKey)
preMasterSecret := make([]byte, (curve.Params().BitSize+7)>>3)
xBytes := x.Bytes()
copy(preMasterSecret[len(preMasterSecret)-len(xBytes):], xBytes)
return preMasterSecret, nil
}
func (ka *ecdheKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, error) {
if ka.curveid == 0 {
return nil, nil, errors.New("tls: missing ServerKeyExchange message")
}
var serialized, preMasterSecret []byte
if ka.curveid == X25519 {
var ourPublic, theirPublic, sharedKey, scalar [32]byte
if _, err := io.ReadFull(config.rand(), scalar[:]); err != nil {
return nil, nil, err
}
copy(theirPublic[:], ka.publicKey)
curve25519.ScalarBaseMult(&ourPublic, &scalar)
curve25519.ScalarMult(&sharedKey, &scalar, &theirPublic)
serialized = ourPublic[:]
preMasterSecret = sharedKey[:]
} else {
curve, ok := curveForCurveID(ka.curveid)
if !ok {
panic("internal error")
}
priv, mx, my, err := elliptic.GenerateKey(curve, config.rand())
if err != nil {
return nil, nil, err
}
x, _ := curve.ScalarMult(ka.x, ka.y, priv)
preMasterSecret = make([]byte, (curve.Params().BitSize+7)>>3)
xBytes := x.Bytes()
copy(preMasterSecret[len(preMasterSecret)-len(xBytes):], xBytes)
serialized = elliptic.Marshal(curve, mx, my)
}
ckx := new(clientKeyExchangeMsg)
ckx.ciphertext = make([]byte, 1+len(serialized))
ckx.ciphertext[0] = byte(len(serialized))
copy(ckx.ciphertext[1:], serialized)
return preMasterSecret, ckx, nil
}