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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 (
"crypto"
"crypto/ecdsa"
"crypto/elliptic"
"crypto/md5"
"crypto/rsa"
"crypto/sha1"
"crypto/x509"
"encoding/asn1"
"errors"
"io"
"math/big"
)
var errClientKeyExchange = errors.New("tls: invalid ClientKeyExchange message")
var errServerKeyExchange = errors.New("tls: invalid ServerKeyExchange message")
// 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, cert *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg) (*serverKeyExchangeMsg, error) {
return nil, nil
}
func (ka rsaKeyAgreement) processClientKeyExchange(config *Config, cert *Certificate, ckx *clientKeyExchangeMsg, version uint16) ([]byte, error) {
if len(ckx.ciphertext) < 2 {
return nil, errClientKeyExchange
}
ciphertext := ckx.ciphertext
if version != VersionSSL30 {
ciphertextLen := int(ckx.ciphertext[0])<<8 | int(ckx.ciphertext[1])
if ciphertextLen != len(ckx.ciphertext)-2 {
return nil, errClientKeyExchange
}
ciphertext = ckx.ciphertext[2:]
}
priv, ok := cert.PrivateKey.(crypto.Decrypter)
if !ok {
return nil, errors.New("tls: certificate private key does not implement crypto.Decrypter")
}
// Perform constant time RSA PKCS#1 v1.5 decryption
preMasterSecret, err := priv.Decrypt(config.rand(), ciphertext, &rsa.PKCS1v15DecryptOptions{SessionKeyLen: 48})
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) error {
return errors.New("tls: unexpected ServerKeyExchange")
}
func (ka rsaKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, 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
}
// sha1Hash calculates a SHA1 hash over the given byte slices.
func sha1Hash(slices [][]byte) []byte {
hsha1 := sha1.New()
for _, slice := range slices {
hsha1.Write(slice)
}
return hsha1.Sum(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(nil))
copy(md5sha1[md5.Size:], sha1Hash(slices))
return md5sha1
}
// hashForServerKeyExchange hashes the given slices and returns their digest
// and the identifier of the hash function used. The sigAndHash argument is
// only used for >= TLS 1.2 and precisely identifies the hash function to use.
func hashForServerKeyExchange(sigAndHash signatureAndHash, version uint16, slices ...[]byte) ([]byte, crypto.Hash, error) {
if version >= VersionTLS12 {
if !isSupportedSignatureAndHash(sigAndHash, supportedSignatureAlgorithms) {
return nil, crypto.Hash(0), errors.New("tls: unsupported hash function used by peer")
}
hashFunc, err := lookupTLSHash(sigAndHash.hash)
if err != nil {
return nil, crypto.Hash(0), err
}
h := hashFunc.New()
for _, slice := range slices {
h.Write(slice)
}
digest := h.Sum(nil)
return digest, hashFunc, nil
}
if sigAndHash.signature == signatureECDSA {
return sha1Hash(slices), crypto.SHA1, nil
}
return md5SHA1Hash(slices), crypto.MD5SHA1, nil
}
// pickTLS12HashForSignature returns a TLS 1.2 hash identifier for signing a
// ServerKeyExchange given the signature type being used and the client's
// advertised list of supported signature and hash combinations.
func pickTLS12HashForSignature(sigType uint8, clientList []signatureAndHash) (uint8, error) {
if len(clientList) == 0 {
// If the client didn't specify any signature_algorithms
// extension then we can assume that it supports SHA1. See
// http://tools.ietf.org/html/rfc5246#section-7.4.1.4.1
return hashSHA1, nil
}
for _, sigAndHash := range clientList {
if sigAndHash.signature != sigType {
continue
}
if isSupportedSignatureAndHash(sigAndHash, supportedSignatureAlgorithms) {
return sigAndHash.hash, nil
}
}
return 0, errors.New("tls: client doesn't support any common hash functions")
}
func curveForCurveID(id CurveID) (elliptic.Curve, bool) {
switch id {
case CurveP256:
return elliptic.P256(), true
case CurveP384:
return elliptic.P384(), true
case CurveP521:
return elliptic.P521(), true
default:
return nil, false
}
}
// 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. The signature may
// either be ECDSA or RSA.
type ecdheKeyAgreement struct {
version uint16
sigType uint8
privateKey []byte
curve elliptic.Curve
x, y *big.Int
}
func (ka *ecdheKeyAgreement) generateServerKeyExchange(config *Config, cert *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg) (*serverKeyExchangeMsg, error) {
var curveid CurveID
preferredCurves := config.curvePreferences()
NextCandidate:
for _, candidate := range preferredCurves {
for _, c := range clientHello.supportedCurves {
if candidate == c {
curveid = c
break NextCandidate
}
}
}
if curveid == 0 {
return nil, errors.New("tls: no supported elliptic curves offered")
}
var ok bool
if ka.curve, ok = curveForCurveID(curveid); !ok {
return nil, errors.New("tls: preferredCurves includes unsupported curve")
}
var x, y *big.Int
var err error
ka.privateKey, x, y, err = elliptic.GenerateKey(ka.curve, config.rand())
if err != nil {
return nil, err
}
ecdhePublic := elliptic.Marshal(ka.curve, 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)
sigAndHash := signatureAndHash{signature: ka.sigType}
if ka.version >= VersionTLS12 {
if sigAndHash.hash, err = pickTLS12HashForSignature(ka.sigType, clientHello.signatureAndHashes); err != nil {
return nil, err
}
}
digest, hashFunc, err := hashForServerKeyExchange(sigAndHash, ka.version, clientHello.random, hello.random, serverECDHParams)
if err != nil {
return nil, err
}
priv, ok := cert.PrivateKey.(crypto.Signer)
if !ok {
return nil, errors.New("tls: certificate private key does not implement crypto.Signer")
}
var sig []byte
switch ka.sigType {
case signatureECDSA:
_, ok := priv.Public().(*ecdsa.PublicKey)
if !ok {
return nil, errors.New("ECDHE ECDSA requires an ECDSA server key")
}
case signatureRSA:
_, ok := priv.Public().(*rsa.PublicKey)
if !ok {
return nil, errors.New("ECDHE RSA requires a RSA server key")
}
default:
return nil, errors.New("unknown ECDHE signature algorithm")
}
sig, err = priv.Sign(config.rand(), digest, hashFunc)
if err != nil {
return nil, errors.New("failed to sign ECDHE parameters: " + err.Error())
}
skx := new(serverKeyExchangeMsg)
sigAndHashLen := 0
if ka.version >= VersionTLS12 {
sigAndHashLen = 2
}
skx.key = make([]byte, len(serverECDHParams)+sigAndHashLen+2+len(sig))
copy(skx.key, serverECDHParams)
k := skx.key[len(serverECDHParams):]
if ka.version >= VersionTLS12 {
k[0] = sigAndHash.hash
k[1] = sigAndHash.signature
k = k[2:]
}
k[0] = byte(len(sig) >> 8)
k[1] = byte(len(sig))
copy(k[2:], sig)
return skx, nil
}
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
}
x, y := elliptic.Unmarshal(ka.curve, ckx.ciphertext[1:])
if x == nil {
return nil, errClientKeyExchange
}
if !ka.curve.IsOnCurve(x, y) {
return nil, errClientKeyExchange
}
x, _ = ka.curve.ScalarMult(x, y, ka.privateKey)
preMasterSecret := make([]byte, (ka.curve.Params().BitSize+7)>>3)
xBytes := x.Bytes()
copy(preMasterSecret[len(preMasterSecret)-len(xBytes):], xBytes)
return preMasterSecret, nil
}
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])
var ok bool
if ka.curve, ok = curveForCurveID(curveid); !ok {
return errors.New("tls: server selected unsupported curve")
}
publicLen := int(skx.key[3])
if publicLen+4 > len(skx.key) {
return errServerKeyExchange
}
ka.x, ka.y = elliptic.Unmarshal(ka.curve, skx.key[4:4+publicLen])
if ka.x == nil {
return errServerKeyExchange
}
if !ka.curve.IsOnCurve(ka.x, ka.y) {
return errServerKeyExchange
}
serverECDHParams := skx.key[:4+publicLen]
sig := skx.key[4+publicLen:]
if len(sig) < 2 {
return errServerKeyExchange
}
sigAndHash := signatureAndHash{signature: ka.sigType}
if ka.version >= VersionTLS12 {
// handle SignatureAndHashAlgorithm
sigAndHash = signatureAndHash{hash: sig[0], signature: sig[1]}
if sigAndHash.signature != ka.sigType {
return errServerKeyExchange
}
sig = sig[2:]
if len(sig) < 2 {
return errServerKeyExchange
}
}
sigLen := int(sig[0])<<8 | int(sig[1])
if sigLen+2 != len(sig) {
return errServerKeyExchange
}
sig = sig[2:]
digest, hashFunc, err := hashForServerKeyExchange(sigAndHash, ka.version, clientHello.random, serverHello.random, serverECDHParams)
if err != nil {
return err
}
switch ka.sigType {
case signatureECDSA:
pubKey, ok := cert.PublicKey.(*ecdsa.PublicKey)
if !ok {
return errors.New("ECDHE ECDSA requires a ECDSA server public key")
}
ecdsaSig := new(ecdsaSignature)
if _, err := asn1.Unmarshal(sig, ecdsaSig); err != nil {
return err
}
if ecdsaSig.R.Sign() <= 0 || ecdsaSig.S.Sign() <= 0 {
return errors.New("ECDSA signature contained zero or negative values")
}
if !ecdsa.Verify(pubKey, digest, ecdsaSig.R, ecdsaSig.S) {
return errors.New("ECDSA verification failure")
}
case signatureRSA:
pubKey, ok := cert.PublicKey.(*rsa.PublicKey)
if !ok {
return errors.New("ECDHE RSA requires a RSA server public key")
}
if err := rsa.VerifyPKCS1v15(pubKey, hashFunc, digest, sig); err != nil {
return err
}
default:
return errors.New("unknown ECDHE signature algorithm")
}
return nil
}
func (ka *ecdheKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, error) {
if ka.curve == nil {
return nil, nil, errors.New("missing ServerKeyExchange message")
}
priv, mx, my, err := elliptic.GenerateKey(ka.curve, config.rand())
if err != nil {
return nil, nil, err
}
x, _ := ka.curve.ScalarMult(ka.x, ka.y, priv)
preMasterSecret := make([]byte, (ka.curve.Params().BitSize+7)>>3)
xBytes := x.Bytes()
copy(preMasterSecret[len(preMasterSecret)-len(xBytes):], xBytes)
serialized := elliptic.Marshal(ka.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
}