Method processServerKeyExchange

key_agreement.go:270–349

(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, skx *serverKeyExchangeMsg)

}

func (ka *ecdheKeyAgreement) processServerKeyExchange(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, skx *serverKeyExchangeMsg) error {
	if len(skx.key) < 4 {
		return errServerKeyExchange
	}
	if skx.key[0] != 3 { // named curve
		return errors.New("tls: server selected unsupported curve")
	}
	curveID := CurveID(skx.key[1])<<8 | CurveID(skx.key[2])

	publicLen := int(skx.key[3])
	if publicLen+4 > len(skx.key) {
		return errServerKeyExchange
	}
	serverECDHEParams := skx.key[:4+publicLen]
	publicKey := serverECDHEParams[4:]

	sig := skx.key[4+publicLen:]
	if len(sig) < 2 {
		return errServerKeyExchange
	}

	if _, ok := curveForCurveID(curveID); curveID != X25519 && !ok {
		return errors.New("tls: server selected unsupported curve")
	}

	params, err := generateECDHEParameters(config.rand(), curveID)
	if err != nil {
		return err
	}
	ka.params = params

	ka.preMasterSecret = params.SharedKey(publicKey)
	if ka.preMasterSecret == nil {
		return errServerKeyExchange
	}

	ourPublicKey := params.PublicKey()
	ka.ckx = new(clientKeyExchangeMsg)
	ka.ckx.ciphertext = make([]byte, 1+len(ourPublicKey))
	ka.ckx.ciphertext[0] = byte(len(ourPublicKey))
	copy(ka.ckx.ciphertext[1:], ourPublicKey)

	var sigType uint8
	var sigHash crypto.Hash
	if ka.version >= VersionTLS12 {
		signatureAlgorithm := SignatureScheme(sig[0])<<8 | SignatureScheme(sig[1])
		sig = sig[2:]
		if len(sig) < 2 {
			return errServerKeyExchange
		}

		if !isSupportedSignatureAlgorithm(signatureAlgorithm, clientHello.supportedSignatureAlgorithms) {
			return errors.New("tls: certificate used with invalid signature algorithm")
		}
		sigType, sigHash, err = typeAndHashFromSignatureScheme(signatureAlgorithm)
		if err != nil {
			return err
		}