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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 (
"big"
"crypto/elliptic"
"crypto/md5"
"crypto/rsa"
"crypto/sha1"
"crypto/x509"
"io"
"os"
)
// rsaKeyAgreement implements the standard TLS key agreement where the client
// encrypts the pre-master secret to the server's public key.
type rsaKeyAgreement struct{}
func (ka rsaKeyAgreement) generateServerKeyExchange(config *Config, clientHello *clientHelloMsg, hello *serverHelloMsg) (*serverKeyExchangeMsg, os.Error) {
return nil, nil
}
func (ka rsaKeyAgreement) processClientKeyExchange(config *Config, ckx *clientKeyExchangeMsg) ([]byte, os.Error) {
preMasterSecret := make([]byte, 48)
_, err := io.ReadFull(config.rand(), preMasterSecret[2:])
if err != nil {
return nil, err
}
if len(ckx.ciphertext) < 2 {
return nil, os.ErrorString("bad ClientKeyExchange")
}
ciphertextLen := int(ckx.ciphertext[0])<<8 | int(ckx.ciphertext[1])
if ciphertextLen != len(ckx.ciphertext)-2 {
return nil, os.ErrorString("bad ClientKeyExchange")
}
ciphertext := ckx.ciphertext[2:]
err = rsa.DecryptPKCS1v15SessionKey(config.rand(), config.Certificates[0].PrivateKey, ciphertext, preMasterSecret)
if err != nil {
return nil, err
}
// We don't check the version number in the premaster secret. For one,
// by checking it, we would leak information about the validity of the
// encrypted pre-master secret. Secondly, it provides only a small
// benefit against a downgrade attack and some implementations send the
// wrong version anyway. See the discussion at the end of section
// 7.4.7.1 of RFC 4346.
return preMasterSecret, nil
}
func (ka rsaKeyAgreement) processServerKeyExchange(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, skx *serverKeyExchangeMsg) os.Error {
return os.ErrorString("unexpected ServerKeyExchange")
}
func (ka rsaKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, os.Error) {
preMasterSecret := make([]byte, 48)
preMasterSecret[0] = byte(clientHello.vers >> 8)
preMasterSecret[1] = byte(clientHello.vers)
_, err := io.ReadFull(config.rand(), preMasterSecret[2:])
if err != nil {
return nil, nil, err
}
encrypted, err := rsa.EncryptPKCS1v15(config.rand(), cert.PublicKey.(*rsa.PublicKey), preMasterSecret)
if err != nil {
return nil, nil, err
}
ckx := new(clientKeyExchangeMsg)
ckx.ciphertext = make([]byte, len(encrypted)+2)
ckx.ciphertext[0] = byte(len(encrypted) >> 8)
ckx.ciphertext[1] = byte(len(encrypted))
copy(ckx.ciphertext[2:], encrypted)
return preMasterSecret, ckx, nil
}
// md5SHA1Hash implements TLS 1.0's hybrid hash function which consists of the
// concatenation of an MD5 and SHA1 hash.
func md5SHA1Hash(slices ...[]byte) []byte {
md5sha1 := make([]byte, md5.Size+sha1.Size)
hmd5 := md5.New()
for _, slice := range slices {
hmd5.Write(slice)
}
copy(md5sha1, hmd5.Sum())
hsha1 := sha1.New()
for _, slice := range slices {
hsha1.Write(slice)
}
copy(md5sha1[md5.Size:], hsha1.Sum())
return md5sha1
}
// ecdheRSAKeyAgreement implements a TLS key agreement where the server
// generates a ephemeral EC public/private key pair and signs it. The
// pre-master secret is then calculated using ECDH.
type ecdheRSAKeyAgreement struct {
privateKey []byte
curve *elliptic.Curve
x, y *big.Int
}
func (ka *ecdheRSAKeyAgreement) generateServerKeyExchange(config *Config, clientHello *clientHelloMsg, hello *serverHelloMsg) (*serverKeyExchangeMsg, os.Error) {
var curveid uint16
Curve:
for _, c := range clientHello.supportedCurves {
switch c {
case curveP256:
ka.curve = elliptic.P256()
curveid = c
break Curve
case curveP384:
ka.curve = elliptic.P384()
curveid = c
break Curve
case curveP521:
ka.curve = elliptic.P521()
curveid = c
break Curve
}
}
var x, y *big.Int
var err os.Error
ka.privateKey, x, y, err = ka.curve.GenerateKey(config.rand())
if err != nil {
return nil, err
}
ecdhePublic := ka.curve.Marshal(x, y)
// http://tools.ietf.org/html/rfc4492#section-5.4
serverECDHParams := make([]byte, 1+2+1+len(ecdhePublic))
serverECDHParams[0] = 3 // named curve
serverECDHParams[1] = byte(curveid >> 8)
serverECDHParams[2] = byte(curveid)
serverECDHParams[3] = byte(len(ecdhePublic))
copy(serverECDHParams[4:], ecdhePublic)
md5sha1 := md5SHA1Hash(clientHello.random, hello.random, serverECDHParams)
sig, err := rsa.SignPKCS1v15(config.rand(), config.Certificates[0].PrivateKey, rsa.HashMD5SHA1, md5sha1)
if err != nil {
return nil, os.ErrorString("failed to sign ECDHE parameters: " + err.String())
}
skx := new(serverKeyExchangeMsg)
skx.key = make([]byte, len(serverECDHParams)+2+len(sig))
copy(skx.key, serverECDHParams)
k := skx.key[len(serverECDHParams):]
k[0] = byte(len(sig) >> 8)
k[1] = byte(len(sig))
copy(k[2:], sig)
return skx, nil
}
func (ka *ecdheRSAKeyAgreement) processClientKeyExchange(config *Config, ckx *clientKeyExchangeMsg) ([]byte, os.Error) {
if len(ckx.ciphertext) == 0 || int(ckx.ciphertext[0]) != len(ckx.ciphertext)-1 {
return nil, os.ErrorString("bad ClientKeyExchange")
}
x, y := ka.curve.Unmarshal(ckx.ciphertext[1:])
if x == nil {
return nil, os.ErrorString("bad ClientKeyExchange")
}
x, _ = ka.curve.ScalarMult(x, y, ka.privateKey)
preMasterSecret := make([]byte, (ka.curve.BitSize+7)>>3)
xBytes := x.Bytes()
copy(preMasterSecret[len(preMasterSecret)-len(xBytes):], xBytes)
return preMasterSecret, nil
}
func (ka *ecdheRSAKeyAgreement) processServerKeyExchange(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, skx *serverKeyExchangeMsg) os.Error {
if len(skx.key) < 4 {
goto Error
}
if skx.key[0] != 3 { // named curve
return os.ErrorString("server selected unsupported curve")
}
curveid := uint16(skx.key[1])<<8 | uint16(skx.key[2])
switch curveid {
case curveP256:
ka.curve = elliptic.P256()
case curveP384:
ka.curve = elliptic.P384()
case curveP521:
ka.curve = elliptic.P521()
default:
return os.ErrorString("server selected unsupported curve")
}
publicLen := int(skx.key[3])
if publicLen+4 > len(skx.key) {
goto Error
}
ka.x, ka.y = ka.curve.Unmarshal(skx.key[4 : 4+publicLen])
if ka.x == nil {
goto Error
}
serverECDHParams := skx.key[:4+publicLen]
sig := skx.key[4+publicLen:]
if len(sig) < 2 {
goto Error
}
sigLen := int(sig[0])<<8 | int(sig[1])
if sigLen+2 != len(sig) {
goto Error
}
sig = sig[2:]
md5sha1 := md5SHA1Hash(clientHello.random, serverHello.random, serverECDHParams)
return rsa.VerifyPKCS1v15(cert.PublicKey.(*rsa.PublicKey), rsa.HashMD5SHA1, md5sha1, sig)
Error:
return os.ErrorString("invalid ServerKeyExchange")
}
func (ka *ecdheRSAKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, os.Error) {
if ka.curve == nil {
return nil, nil, os.ErrorString("missing ServerKeyExchange message")
}
priv, mx, my, err := ka.curve.GenerateKey(config.rand())
if err != nil {
return nil, nil, err
}
x, _ := ka.curve.ScalarMult(ka.x, ka.y, priv)
preMasterSecret := make([]byte, (ka.curve.BitSize+7)>>3)
xBytes := x.Bytes()
copy(preMasterSecret[len(preMasterSecret)-len(xBytes):], xBytes)
serialised := ka.curve.Marshal(mx, my)
ckx := new(clientKeyExchangeMsg)
ckx.ciphertext = make([]byte, 1+len(serialised))
ckx.ciphertext[0] = byte(len(serialised))
copy(ckx.ciphertext[1:], serialised)
return preMasterSecret, ckx, nil
}
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