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// Copyright 2010 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 tls
import (
// a keyAgreement implements the client and server side of a TLS key agreement
// protocol by generating and processing key exchange messages.
type keyAgreement interface {
// On the server side, the first two methods are called in order.
// In the case that the key agreement protocol doesn't use a
// ServerKeyExchange message, generateServerKeyExchange can return nil,
// nil.
generateServerKeyExchange(*Config, *clientHelloMsg, *serverHelloMsg) (*serverKeyExchangeMsg, os.Error)
processClientKeyExchange(*Config, *clientKeyExchangeMsg) ([]byte, os.Error)
// On the client side, the next two methods are called in order.
// This method may not be called if the server doesn't send a
// ServerKeyExchange message.
processServerKeyExchange(*Config, *clientHelloMsg, *serverHelloMsg, *x509.Certificate, *serverKeyExchangeMsg) os.Error
generateClientKeyExchange(*Config, *clientHelloMsg, *x509.Certificate) ([]byte, *clientKeyExchangeMsg, os.Error)
// A cipherSuite is a specific combination of key agreement, cipher and MAC
// function. All cipher suites currently assume RSA key agreement.
type cipherSuite struct {
// the lengths, in bytes, of the key material needed for each component.
keyLen int
macLen int
ivLen int
ka func() keyAgreement
// If elliptic is set, a server will only consider this ciphersuite if
// the ClientHello indicated that the client supports an elliptic curve
// and point format that we can handle.
elliptic bool
cipher func(key, iv []byte, isRead bool) interface{}
mac func(macKey []byte) hash.Hash
var cipherSuites = map[uint16]*cipherSuite{
TLS_RSA_WITH_RC4_128_SHA: &cipherSuite{16, 20, 0, rsaKA, false, cipherRC4, hmacSHA1},
TLS_RSA_WITH_AES_128_CBC_SHA: &cipherSuite{16, 20, 16, rsaKA, false, cipherAES, hmacSHA1},
TLS_ECDHE_RSA_WITH_RC4_128_SHA: &cipherSuite{16, 20, 0, ecdheRSAKA, true, cipherRC4, hmacSHA1},
TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA: &cipherSuite{16, 20, 16, ecdheRSAKA, true, cipherAES, hmacSHA1},
func cipherRC4(key, iv []byte, isRead bool) interface{} {
cipher, _ := rc4.NewCipher(key)
return cipher
func cipherAES(key, iv []byte, isRead bool) interface{} {
block, _ := aes.NewCipher(key)
if isRead {
return cipher.NewCBCDecrypter(block, iv)
return cipher.NewCBCEncrypter(block, iv)
func hmacSHA1(key []byte) hash.Hash {
return hmac.NewSHA1(key)
func rsaKA() keyAgreement {
return rsaKeyAgreement{}
func ecdheRSAKA() keyAgreement {
return new(ecdheRSAKeyAgreement)
// mutualCipherSuite returns a cipherSuite and its id given a list of supported
// ciphersuites and the id requested by the peer.
func mutualCipherSuite(have []uint16, want uint16) (suite *cipherSuite, id uint16) {
for _, id := range have {
if id == want {
return cipherSuites[id], id
// A list of the possible cipher suite ids. Taken from
const (
TLS_RSA_WITH_RC4_128_SHA uint16 = 0x0005
TLS_RSA_WITH_AES_128_CBC_SHA uint16 = 0x002f
TLS_ECDHE_RSA_WITH_RC4_128_SHA uint16 = 0xc011
TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA uint16 = 0xc013