1 // Copyright 2010 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
23 var errClientKeyExchange = errors.New("tls: invalid ClientKeyExchange message")
24 var errServerKeyExchange = errors.New("tls: invalid ServerKeyExchange message")
26 // rsaKeyAgreement implements the standard TLS key agreement where the client
27 // encrypts the pre-master secret to the server's public key.
28 type rsaKeyAgreement struct{}
30 func (ka rsaKeyAgreement) generateServerKeyExchange(config *Config, cert *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg) (*serverKeyExchangeMsg, error) {
34 func (ka rsaKeyAgreement) processClientKeyExchange(config *Config, cert *Certificate, ckx *clientKeyExchangeMsg, version uint16) ([]byte, error) {
35 preMasterSecret := make([]byte, 48)
36 _, err := io.ReadFull(config.rand(), preMasterSecret[2:])
41 if len(ckx.ciphertext) < 2 {
42 return nil, errClientKeyExchange
45 ciphertext := ckx.ciphertext
46 if version != VersionSSL30 {
47 ciphertextLen := int(ckx.ciphertext[0])<<8 | int(ckx.ciphertext[1])
48 if ciphertextLen != len(ckx.ciphertext)-2 {
49 return nil, errClientKeyExchange
51 ciphertext = ckx.ciphertext[2:]
54 err = rsa.DecryptPKCS1v15SessionKey(config.rand(), cert.PrivateKey.(*rsa.PrivateKey), ciphertext, preMasterSecret)
58 // We don't check the version number in the premaster secret. For one,
59 // by checking it, we would leak information about the validity of the
60 // encrypted pre-master secret. Secondly, it provides only a small
61 // benefit against a downgrade attack and some implementations send the
62 // wrong version anyway. See the discussion at the end of section
63 // 7.4.7.1 of RFC 4346.
64 return preMasterSecret, nil
67 func (ka rsaKeyAgreement) processServerKeyExchange(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, skx *serverKeyExchangeMsg) error {
68 return errors.New("tls: unexpected ServerKeyExchange")
71 func (ka rsaKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, error) {
72 preMasterSecret := make([]byte, 48)
73 preMasterSecret[0] = byte(clientHello.vers >> 8)
74 preMasterSecret[1] = byte(clientHello.vers)
75 _, err := io.ReadFull(config.rand(), preMasterSecret[2:])
80 encrypted, err := rsa.EncryptPKCS1v15(config.rand(), cert.PublicKey.(*rsa.PublicKey), preMasterSecret)
84 ckx := new(clientKeyExchangeMsg)
85 ckx.ciphertext = make([]byte, len(encrypted)+2)
86 ckx.ciphertext[0] = byte(len(encrypted) >> 8)
87 ckx.ciphertext[1] = byte(len(encrypted))
88 copy(ckx.ciphertext[2:], encrypted)
89 return preMasterSecret, ckx, nil
92 // sha1Hash calculates a SHA1 hash over the given byte slices.
93 func sha1Hash(slices [][]byte) []byte {
95 for _, slice := range slices {
101 // md5SHA1Hash implements TLS 1.0's hybrid hash function which consists of the
102 // concatenation of an MD5 and SHA1 hash.
103 func md5SHA1Hash(slices [][]byte) []byte {
104 md5sha1 := make([]byte, md5.Size+sha1.Size)
106 for _, slice := range slices {
109 copy(md5sha1, hmd5.Sum(nil))
110 copy(md5sha1[md5.Size:], sha1Hash(slices))
114 // sha256Hash implements TLS 1.2's hash function.
115 func sha256Hash(slices [][]byte) []byte {
117 for _, slice := range slices {
123 // hashForServerKeyExchange hashes the given slices and returns their digest
124 // and the identifier of the hash function used. The hashFunc argument is only
125 // used for >= TLS 1.2 and precisely identifies the hash function to use.
126 func hashForServerKeyExchange(sigType, hashFunc uint8, version uint16, slices ...[]byte) ([]byte, crypto.Hash, error) {
127 if version >= VersionTLS12 {
130 return sha256Hash(slices), crypto.SHA256, nil
132 return sha1Hash(slices), crypto.SHA1, nil
134 return nil, crypto.Hash(0), errors.New("tls: unknown hash function used by peer")
137 if sigType == signatureECDSA {
138 return sha1Hash(slices), crypto.SHA1, nil
140 return md5SHA1Hash(slices), crypto.MD5SHA1, nil
143 // pickTLS12HashForSignature returns a TLS 1.2 hash identifier for signing a
144 // ServerKeyExchange given the signature type being used and the client's
145 // advertized list of supported signature and hash combinations.
146 func pickTLS12HashForSignature(sigType uint8, clientSignatureAndHashes []signatureAndHash) (uint8, error) {
147 if len(clientSignatureAndHashes) == 0 {
148 // If the client didn't specify any signature_algorithms
149 // extension then we can assume that it supports SHA1. See
150 // http://tools.ietf.org/html/rfc5246#section-7.4.1.4.1
154 for _, sigAndHash := range clientSignatureAndHashes {
155 if sigAndHash.signature != sigType {
158 switch sigAndHash.hash {
159 case hashSHA1, hashSHA256:
160 return sigAndHash.hash, nil
164 return 0, errors.New("tls: client doesn't support any common hash functions")
167 func curveForCurveID(id CurveID) (elliptic.Curve, bool) {
170 return elliptic.P256(), true
172 return elliptic.P384(), true
174 return elliptic.P521(), true
181 // signedKeyAgreement implements helper functions for key agreement
182 // methods that involve signed parameters in the ServerKeyExchange.
183 type signedKeyAgreement struct {
188 func (ka *signedKeyAgreement) signParameters(config *Config, cert *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg, params []byte) (*serverKeyExchangeMsg, error) {
189 var tls12HashId uint8
191 if ka.version >= VersionTLS12 {
192 if tls12HashId, err = pickTLS12HashForSignature(ka.sigType, clientHello.signatureAndHashes); err != nil {
197 digest, hashFunc, err := hashForServerKeyExchange(ka.sigType, tls12HashId, ka.version, clientHello.random, hello.random, params)
202 if config.Bugs.InvalidSKXSignature {
209 privKey, ok := cert.PrivateKey.(*ecdsa.PrivateKey)
211 return nil, errors.New("ECDHE ECDSA requires an ECDSA server private key")
213 r, s, err := ecdsa.Sign(config.rand(), privKey, digest)
215 return nil, errors.New("failed to sign ECDHE parameters: " + err.Error())
217 order := privKey.Curve.Params().N
218 r = maybeCorruptECDSAValue(r, config.Bugs.BadECDSAR, order)
219 s = maybeCorruptECDSAValue(s, config.Bugs.BadECDSAS, order)
220 sig, err = asn1.Marshal(ecdsaSignature{r, s})
222 privKey, ok := cert.PrivateKey.(*rsa.PrivateKey)
224 return nil, errors.New("ECDHE RSA requires a RSA server private key")
226 sig, err = rsa.SignPKCS1v15(config.rand(), privKey, hashFunc, digest)
228 return nil, errors.New("failed to sign ECDHE parameters: " + err.Error())
231 return nil, errors.New("unknown ECDHE signature algorithm")
234 skx := new(serverKeyExchangeMsg)
235 if config.Bugs.UnauthenticatedECDH {
239 if ka.version >= VersionTLS12 {
242 skx.key = make([]byte, len(params)+sigAndHashLen+2+len(sig))
243 copy(skx.key, params)
244 k := skx.key[len(params):]
245 if ka.version >= VersionTLS12 {
250 k[0] = byte(len(sig) >> 8)
251 k[1] = byte(len(sig))
258 func (ka *signedKeyAgreement) verifyParameters(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, params []byte, sig []byte) error {
260 return errServerKeyExchange
263 var tls12HashId uint8
264 if ka.version >= VersionTLS12 {
265 // handle SignatureAndHashAlgorithm
266 var sigAndHash []uint8
267 sigAndHash, sig = sig[:2], sig[2:]
268 if sigAndHash[1] != ka.sigType {
269 return errServerKeyExchange
271 tls12HashId = sigAndHash[0]
273 return errServerKeyExchange
276 sigLen := int(sig[0])<<8 | int(sig[1])
277 if sigLen+2 != len(sig) {
278 return errServerKeyExchange
282 digest, hashFunc, err := hashForServerKeyExchange(ka.sigType, tls12HashId, ka.version, clientHello.random, serverHello.random, params)
288 pubKey, ok := cert.PublicKey.(*ecdsa.PublicKey)
290 return errors.New("ECDHE ECDSA requires a ECDSA server public key")
292 ecdsaSig := new(ecdsaSignature)
293 if _, err := asn1.Unmarshal(sig, ecdsaSig); err != nil {
296 if ecdsaSig.R.Sign() <= 0 || ecdsaSig.S.Sign() <= 0 {
297 return errors.New("ECDSA signature contained zero or negative values")
299 if !ecdsa.Verify(pubKey, digest, ecdsaSig.R, ecdsaSig.S) {
300 return errors.New("ECDSA verification failure")
303 pubKey, ok := cert.PublicKey.(*rsa.PublicKey)
305 return errors.New("ECDHE RSA requires a RSA server public key")
307 if err := rsa.VerifyPKCS1v15(pubKey, hashFunc, digest, sig); err != nil {
311 return errors.New("unknown ECDHE signature algorithm")
317 // ecdheRSAKeyAgreement implements a TLS key agreement where the server
318 // generates a ephemeral EC public/private key pair and signs it. The
319 // pre-master secret is then calculated using ECDH. The signature may
320 // either be ECDSA or RSA.
321 type ecdheKeyAgreement struct {
328 func maybeCorruptECDSAValue(n *big.Int, typeOfCorruption BadValue, limit *big.Int) *big.Int {
329 switch typeOfCorruption {
332 case BadValueNegative:
333 return new(big.Int).Neg(n)
339 bad := new(big.Int).Set(limit)
340 return bad.Lsh(bad, 20)
342 panic("unknown BadValue type")
346 func (ka *ecdheKeyAgreement) generateServerKeyExchange(config *Config, cert *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg) (*serverKeyExchangeMsg, error) {
348 preferredCurves := config.curvePreferences()
351 for _, candidate := range preferredCurves {
352 for _, c := range clientHello.supportedCurves {
361 return nil, errors.New("tls: no supported elliptic curves offered")
365 if ka.curve, ok = curveForCurveID(curveid); !ok {
366 return nil, errors.New("tls: preferredCurves includes unsupported curve")
371 ka.privateKey, x, y, err = elliptic.GenerateKey(ka.curve, config.rand())
375 ecdhePublic := elliptic.Marshal(ka.curve, x, y)
377 // http://tools.ietf.org/html/rfc4492#section-5.4
378 serverECDHParams := make([]byte, 1+2+1+len(ecdhePublic))
379 serverECDHParams[0] = 3 // named curve
380 serverECDHParams[1] = byte(curveid >> 8)
381 serverECDHParams[2] = byte(curveid)
382 if config.Bugs.InvalidSKXCurve {
383 serverECDHParams[2] ^= 0xff
385 serverECDHParams[3] = byte(len(ecdhePublic))
386 copy(serverECDHParams[4:], ecdhePublic)
388 return ka.signParameters(config, cert, clientHello, hello, serverECDHParams)
391 func (ka *ecdheKeyAgreement) processClientKeyExchange(config *Config, cert *Certificate, ckx *clientKeyExchangeMsg, version uint16) ([]byte, error) {
392 if len(ckx.ciphertext) == 0 || int(ckx.ciphertext[0]) != len(ckx.ciphertext)-1 {
393 return nil, errClientKeyExchange
395 x, y := elliptic.Unmarshal(ka.curve, ckx.ciphertext[1:])
397 return nil, errClientKeyExchange
399 x, _ = ka.curve.ScalarMult(x, y, ka.privateKey)
400 preMasterSecret := make([]byte, (ka.curve.Params().BitSize+7)>>3)
402 copy(preMasterSecret[len(preMasterSecret)-len(xBytes):], xBytes)
404 return preMasterSecret, nil
407 func (ka *ecdheKeyAgreement) processServerKeyExchange(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, skx *serverKeyExchangeMsg) error {
408 if len(skx.key) < 4 {
409 return errServerKeyExchange
411 if skx.key[0] != 3 { // named curve
412 return errors.New("tls: server selected unsupported curve")
414 curveid := CurveID(skx.key[1])<<8 | CurveID(skx.key[2])
417 if ka.curve, ok = curveForCurveID(curveid); !ok {
418 return errors.New("tls: server selected unsupported curve")
421 publicLen := int(skx.key[3])
422 if publicLen+4 > len(skx.key) {
423 return errServerKeyExchange
425 ka.x, ka.y = elliptic.Unmarshal(ka.curve, skx.key[4:4+publicLen])
427 return errServerKeyExchange
429 serverECDHParams := skx.key[:4+publicLen]
430 sig := skx.key[4+publicLen:]
432 return ka.verifyParameters(config, clientHello, serverHello, cert, serverECDHParams, sig)
435 func (ka *ecdheKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, error) {
437 return nil, nil, errors.New("missing ServerKeyExchange message")
439 priv, mx, my, err := elliptic.GenerateKey(ka.curve, config.rand())
443 x, _ := ka.curve.ScalarMult(ka.x, ka.y, priv)
444 preMasterSecret := make([]byte, (ka.curve.Params().BitSize+7)>>3)
446 copy(preMasterSecret[len(preMasterSecret)-len(xBytes):], xBytes)
448 serialized := elliptic.Marshal(ka.curve, mx, my)
450 ckx := new(clientKeyExchangeMsg)
451 ckx.ciphertext = make([]byte, 1+len(serialized))
452 ckx.ciphertext[0] = byte(len(serialized))
453 copy(ckx.ciphertext[1:], serialized)
455 return preMasterSecret, ckx, nil
458 // dheRSAKeyAgreement implements a TLS key agreement where the server generates
459 // an ephemeral Diffie-Hellman public/private key pair and signs it. The
460 // pre-master secret is then calculated using Diffie-Hellman.
461 type dheKeyAgreement struct {
468 func (ka *dheKeyAgreement) generateServerKeyExchange(config *Config, cert *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg) (*serverKeyExchangeMsg, error) {
469 // 2048-bit MODP Group with 256-bit Prime Order Subgroup (RFC
470 // 5114, Section 2.3)
471 ka.p, _ = new(big.Int).SetString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
472 ka.g, _ = new(big.Int).SetString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
473 q, _ := new(big.Int).SetString("8CF83642A709A097B447997640129DA299B1A47D1EB3750BA308B0FE64F5FBD3", 16)
476 ka.xOurs, err = rand.Int(config.rand(), q)
480 yOurs := new(big.Int).Exp(ka.g, ka.xOurs, ka.p)
482 // http://tools.ietf.org/html/rfc5246#section-7.4.3
483 pBytes := ka.p.Bytes()
484 gBytes := ka.g.Bytes()
485 yBytes := yOurs.Bytes()
486 serverDHParams := make([]byte, 0, 2+len(pBytes)+2+len(gBytes)+2+len(yBytes))
487 serverDHParams = append(serverDHParams, byte(len(pBytes)>>8), byte(len(pBytes)))
488 serverDHParams = append(serverDHParams, pBytes...)
489 serverDHParams = append(serverDHParams, byte(len(gBytes)>>8), byte(len(gBytes)))
490 serverDHParams = append(serverDHParams, gBytes...)
491 serverDHParams = append(serverDHParams, byte(len(yBytes)>>8), byte(len(yBytes)))
492 serverDHParams = append(serverDHParams, yBytes...)
494 return ka.signParameters(config, cert, clientHello, hello, serverDHParams)
497 func (ka *dheKeyAgreement) processClientKeyExchange(config *Config, cert *Certificate, ckx *clientKeyExchangeMsg, version uint16) ([]byte, error) {
498 if len(ckx.ciphertext) < 2 {
499 return nil, errClientKeyExchange
501 yLen := (int(ckx.ciphertext[0]) << 8) | int(ckx.ciphertext[1])
502 if yLen != len(ckx.ciphertext)-2 {
503 return nil, errClientKeyExchange
505 yTheirs := new(big.Int).SetBytes(ckx.ciphertext[2:])
506 if yTheirs.Sign() <= 0 || yTheirs.Cmp(ka.p) >= 0 {
507 return nil, errClientKeyExchange
509 return new(big.Int).Exp(yTheirs, ka.xOurs, ka.p).Bytes(), nil
512 func (ka *dheKeyAgreement) processServerKeyExchange(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, skx *serverKeyExchangeMsg) error {
516 return errServerKeyExchange
518 pLen := (int(k[0]) << 8) | int(k[1])
521 return errServerKeyExchange
523 ka.p = new(big.Int).SetBytes(k[:pLen])
528 return errServerKeyExchange
530 gLen := (int(k[0]) << 8) | int(k[1])
533 return errServerKeyExchange
535 ka.g = new(big.Int).SetBytes(k[:gLen])
540 return errServerKeyExchange
542 yLen := (int(k[0]) << 8) | int(k[1])
545 return errServerKeyExchange
547 ka.yTheirs = new(big.Int).SetBytes(k[:yLen])
549 if ka.yTheirs.Sign() <= 0 || ka.yTheirs.Cmp(ka.p) >= 0 {
550 return errServerKeyExchange
554 serverDHParams := skx.key[:len(skx.key)-len(sig)]
556 return ka.verifyParameters(config, clientHello, serverHello, cert, serverDHParams, sig)
559 func (ka *dheKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, error) {
560 if ka.p == nil || ka.g == nil || ka.yTheirs == nil {
561 return nil, nil, errors.New("missing ServerKeyExchange message")
564 xOurs, err := rand.Int(config.rand(), ka.p)
568 preMasterSecret := new(big.Int).Exp(ka.yTheirs, xOurs, ka.p).Bytes()
570 yOurs := new(big.Int).Exp(ka.g, xOurs, ka.p)
571 yBytes := yOurs.Bytes()
572 ckx := new(clientKeyExchangeMsg)
573 ckx.ciphertext = make([]byte, 2+len(yBytes))
574 ckx.ciphertext[0] = byte(len(yBytes) >> 8)
575 ckx.ciphertext[1] = byte(len(yBytes))
576 copy(ckx.ciphertext[2:], yBytes)
578 return preMasterSecret, ckx, nil