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 vers := clientHello.vers
74 if config.Bugs.RsaClientKeyExchangeVersion != 0 {
75 vers = config.Bugs.RsaClientKeyExchangeVersion
77 vers = versionToWire(vers, clientHello.isDTLS)
78 preMasterSecret[0] = byte(vers >> 8)
79 preMasterSecret[1] = byte(vers)
80 _, err := io.ReadFull(config.rand(), preMasterSecret[2:])
85 encrypted, err := rsa.EncryptPKCS1v15(config.rand(), cert.PublicKey.(*rsa.PublicKey), preMasterSecret)
89 ckx := new(clientKeyExchangeMsg)
90 if clientHello.vers != VersionSSL30 && !config.Bugs.SSL3RSAKeyExchange {
91 ckx.ciphertext = make([]byte, len(encrypted)+2)
92 ckx.ciphertext[0] = byte(len(encrypted) >> 8)
93 ckx.ciphertext[1] = byte(len(encrypted))
94 copy(ckx.ciphertext[2:], encrypted)
96 ckx.ciphertext = encrypted
98 return preMasterSecret, ckx, nil
101 // sha1Hash calculates a SHA1 hash over the given byte slices.
102 func sha1Hash(slices [][]byte) []byte {
104 for _, slice := range slices {
107 return hsha1.Sum(nil)
110 // md5SHA1Hash implements TLS 1.0's hybrid hash function which consists of the
111 // concatenation of an MD5 and SHA1 hash.
112 func md5SHA1Hash(slices [][]byte) []byte {
113 md5sha1 := make([]byte, md5.Size+sha1.Size)
115 for _, slice := range slices {
118 copy(md5sha1, hmd5.Sum(nil))
119 copy(md5sha1[md5.Size:], sha1Hash(slices))
123 // sha256Hash implements TLS 1.2's hash function.
124 func sha256Hash(slices [][]byte) []byte {
126 for _, slice := range slices {
132 // hashForServerKeyExchange hashes the given slices and returns their digest
133 // and the identifier of the hash function used. The hashFunc argument is only
134 // used for >= TLS 1.2 and precisely identifies the hash function to use.
135 func hashForServerKeyExchange(sigType, hashFunc uint8, version uint16, slices ...[]byte) ([]byte, crypto.Hash, error) {
136 if version >= VersionTLS12 {
139 return sha256Hash(slices), crypto.SHA256, nil
141 return sha1Hash(slices), crypto.SHA1, nil
143 return nil, crypto.Hash(0), errors.New("tls: unknown hash function used by peer")
146 if sigType == signatureECDSA {
147 return sha1Hash(slices), crypto.SHA1, nil
149 return md5SHA1Hash(slices), crypto.MD5SHA1, nil
152 // pickTLS12HashForSignature returns a TLS 1.2 hash identifier for signing a
153 // ServerKeyExchange given the signature type being used and the client's
154 // advertized list of supported signature and hash combinations.
155 func pickTLS12HashForSignature(sigType uint8, clientSignatureAndHashes []signatureAndHash) (uint8, error) {
156 if len(clientSignatureAndHashes) == 0 {
157 // If the client didn't specify any signature_algorithms
158 // extension then we can assume that it supports SHA1. See
159 // http://tools.ietf.org/html/rfc5246#section-7.4.1.4.1
163 for _, sigAndHash := range clientSignatureAndHashes {
164 if sigAndHash.signature != sigType {
167 switch sigAndHash.hash {
168 case hashSHA1, hashSHA256:
169 return sigAndHash.hash, nil
173 return 0, errors.New("tls: client doesn't support any common hash functions")
176 func curveForCurveID(id CurveID) (elliptic.Curve, bool) {
179 return elliptic.P256(), true
181 return elliptic.P384(), true
183 return elliptic.P521(), true
190 // keyAgreementAuthentication is a helper interface that specifies how
191 // to authenticate the ServerKeyExchange parameters.
192 type keyAgreementAuthentication interface {
193 signParameters(config *Config, cert *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg, params []byte) (*serverKeyExchangeMsg, error)
194 verifyParameters(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, params []byte, sig []byte) error
197 // nilKeyAgreementAuthentication does not authenticate the key
198 // agreement parameters.
199 type nilKeyAgreementAuthentication struct{}
201 func (ka *nilKeyAgreementAuthentication) signParameters(config *Config, cert *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg, params []byte) (*serverKeyExchangeMsg, error) {
202 skx := new(serverKeyExchangeMsg)
207 func (ka *nilKeyAgreementAuthentication) verifyParameters(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, params []byte, sig []byte) error {
211 // signedKeyAgreement signs the ServerKeyExchange parameters with the
212 // server's private key.
213 type signedKeyAgreement struct {
218 func (ka *signedKeyAgreement) signParameters(config *Config, cert *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg, params []byte) (*serverKeyExchangeMsg, error) {
219 var tls12HashId uint8
221 if ka.version >= VersionTLS12 {
222 if tls12HashId, err = pickTLS12HashForSignature(ka.sigType, clientHello.signatureAndHashes); err != nil {
227 digest, hashFunc, err := hashForServerKeyExchange(ka.sigType, tls12HashId, ka.version, clientHello.random, hello.random, params)
232 if config.Bugs.InvalidSKXSignature {
239 privKey, ok := cert.PrivateKey.(*ecdsa.PrivateKey)
241 return nil, errors.New("ECDHE ECDSA requires an ECDSA server private key")
243 r, s, err := ecdsa.Sign(config.rand(), privKey, digest)
245 return nil, errors.New("failed to sign ECDHE parameters: " + err.Error())
247 order := privKey.Curve.Params().N
248 r = maybeCorruptECDSAValue(r, config.Bugs.BadECDSAR, order)
249 s = maybeCorruptECDSAValue(s, config.Bugs.BadECDSAS, order)
250 sig, err = asn1.Marshal(ecdsaSignature{r, s})
252 privKey, ok := cert.PrivateKey.(*rsa.PrivateKey)
254 return nil, errors.New("ECDHE RSA requires a RSA server private key")
256 sig, err = rsa.SignPKCS1v15(config.rand(), privKey, hashFunc, digest)
258 return nil, errors.New("failed to sign ECDHE parameters: " + err.Error())
261 return nil, errors.New("unknown ECDHE signature algorithm")
264 skx := new(serverKeyExchangeMsg)
265 if config.Bugs.UnauthenticatedECDH {
269 if ka.version >= VersionTLS12 {
272 skx.key = make([]byte, len(params)+sigAndHashLen+2+len(sig))
273 copy(skx.key, params)
274 k := skx.key[len(params):]
275 if ka.version >= VersionTLS12 {
280 k[0] = byte(len(sig) >> 8)
281 k[1] = byte(len(sig))
288 func (ka *signedKeyAgreement) verifyParameters(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, params []byte, sig []byte) error {
290 return errServerKeyExchange
293 var tls12HashId uint8
294 if ka.version >= VersionTLS12 {
295 // handle SignatureAndHashAlgorithm
296 var sigAndHash []uint8
297 sigAndHash, sig = sig[:2], sig[2:]
298 if sigAndHash[1] != ka.sigType {
299 return errServerKeyExchange
301 tls12HashId = sigAndHash[0]
303 return errServerKeyExchange
306 sigLen := int(sig[0])<<8 | int(sig[1])
307 if sigLen+2 != len(sig) {
308 return errServerKeyExchange
312 digest, hashFunc, err := hashForServerKeyExchange(ka.sigType, tls12HashId, ka.version, clientHello.random, serverHello.random, params)
318 pubKey, ok := cert.PublicKey.(*ecdsa.PublicKey)
320 return errors.New("ECDHE ECDSA requires a ECDSA server public key")
322 ecdsaSig := new(ecdsaSignature)
323 if _, err := asn1.Unmarshal(sig, ecdsaSig); err != nil {
326 if ecdsaSig.R.Sign() <= 0 || ecdsaSig.S.Sign() <= 0 {
327 return errors.New("ECDSA signature contained zero or negative values")
329 if !ecdsa.Verify(pubKey, digest, ecdsaSig.R, ecdsaSig.S) {
330 return errors.New("ECDSA verification failure")
333 pubKey, ok := cert.PublicKey.(*rsa.PublicKey)
335 return errors.New("ECDHE RSA requires a RSA server public key")
337 if err := rsa.VerifyPKCS1v15(pubKey, hashFunc, digest, sig); err != nil {
341 return errors.New("unknown ECDHE signature algorithm")
347 // ecdheRSAKeyAgreement implements a TLS key agreement where the server
348 // generates a ephemeral EC public/private key pair and signs it. The
349 // pre-master secret is then calculated using ECDH. The signature may
350 // either be ECDSA or RSA.
351 type ecdheKeyAgreement struct {
352 auth keyAgreementAuthentication
358 func maybeCorruptECDSAValue(n *big.Int, typeOfCorruption BadValue, limit *big.Int) *big.Int {
359 switch typeOfCorruption {
362 case BadValueNegative:
363 return new(big.Int).Neg(n)
369 bad := new(big.Int).Set(limit)
370 return bad.Lsh(bad, 20)
372 panic("unknown BadValue type")
376 func (ka *ecdheKeyAgreement) generateServerKeyExchange(config *Config, cert *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg) (*serverKeyExchangeMsg, error) {
378 preferredCurves := config.curvePreferences()
381 for _, candidate := range preferredCurves {
382 for _, c := range clientHello.supportedCurves {
391 return nil, errors.New("tls: no supported elliptic curves offered")
395 if ka.curve, ok = curveForCurveID(curveid); !ok {
396 return nil, errors.New("tls: preferredCurves includes unsupported curve")
401 ka.privateKey, x, y, err = elliptic.GenerateKey(ka.curve, config.rand())
405 ecdhePublic := elliptic.Marshal(ka.curve, x, y)
407 // http://tools.ietf.org/html/rfc4492#section-5.4
408 serverECDHParams := make([]byte, 1+2+1+len(ecdhePublic))
409 serverECDHParams[0] = 3 // named curve
410 serverECDHParams[1] = byte(curveid >> 8)
411 serverECDHParams[2] = byte(curveid)
412 if config.Bugs.InvalidSKXCurve {
413 serverECDHParams[2] ^= 0xff
415 serverECDHParams[3] = byte(len(ecdhePublic))
416 copy(serverECDHParams[4:], ecdhePublic)
418 return ka.auth.signParameters(config, cert, clientHello, hello, serverECDHParams)
421 func (ka *ecdheKeyAgreement) processClientKeyExchange(config *Config, cert *Certificate, ckx *clientKeyExchangeMsg, version uint16) ([]byte, error) {
422 if len(ckx.ciphertext) == 0 || int(ckx.ciphertext[0]) != len(ckx.ciphertext)-1 {
423 return nil, errClientKeyExchange
425 x, y := elliptic.Unmarshal(ka.curve, ckx.ciphertext[1:])
427 return nil, errClientKeyExchange
429 x, _ = ka.curve.ScalarMult(x, y, ka.privateKey)
430 preMasterSecret := make([]byte, (ka.curve.Params().BitSize+7)>>3)
432 copy(preMasterSecret[len(preMasterSecret)-len(xBytes):], xBytes)
434 return preMasterSecret, nil
437 func (ka *ecdheKeyAgreement) processServerKeyExchange(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, skx *serverKeyExchangeMsg) error {
438 if len(skx.key) < 4 {
439 return errServerKeyExchange
441 if skx.key[0] != 3 { // named curve
442 return errors.New("tls: server selected unsupported curve")
444 curveid := CurveID(skx.key[1])<<8 | CurveID(skx.key[2])
447 if ka.curve, ok = curveForCurveID(curveid); !ok {
448 return errors.New("tls: server selected unsupported curve")
451 publicLen := int(skx.key[3])
452 if publicLen+4 > len(skx.key) {
453 return errServerKeyExchange
455 ka.x, ka.y = elliptic.Unmarshal(ka.curve, skx.key[4:4+publicLen])
457 return errServerKeyExchange
459 serverECDHParams := skx.key[:4+publicLen]
460 sig := skx.key[4+publicLen:]
462 return ka.auth.verifyParameters(config, clientHello, serverHello, cert, serverECDHParams, sig)
465 func (ka *ecdheKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, error) {
467 return nil, nil, errors.New("missing ServerKeyExchange message")
469 priv, mx, my, err := elliptic.GenerateKey(ka.curve, config.rand())
473 x, _ := ka.curve.ScalarMult(ka.x, ka.y, priv)
474 preMasterSecret := make([]byte, (ka.curve.Params().BitSize+7)>>3)
476 copy(preMasterSecret[len(preMasterSecret)-len(xBytes):], xBytes)
478 serialized := elliptic.Marshal(ka.curve, mx, my)
480 ckx := new(clientKeyExchangeMsg)
481 ckx.ciphertext = make([]byte, 1+len(serialized))
482 ckx.ciphertext[0] = byte(len(serialized))
483 copy(ckx.ciphertext[1:], serialized)
485 return preMasterSecret, ckx, nil
488 // dheRSAKeyAgreement implements a TLS key agreement where the server generates
489 // an ephemeral Diffie-Hellman public/private key pair and signs it. The
490 // pre-master secret is then calculated using Diffie-Hellman.
491 type dheKeyAgreement struct {
492 auth keyAgreementAuthentication
498 func (ka *dheKeyAgreement) generateServerKeyExchange(config *Config, cert *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg) (*serverKeyExchangeMsg, error) {
499 // 2048-bit MODP Group with 256-bit Prime Order Subgroup (RFC
500 // 5114, Section 2.3)
501 ka.p, _ = new(big.Int).SetString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
502 ka.g, _ = new(big.Int).SetString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
503 q, _ := new(big.Int).SetString("8CF83642A709A097B447997640129DA299B1A47D1EB3750BA308B0FE64F5FBD3", 16)
506 ka.xOurs, err = rand.Int(config.rand(), q)
510 yOurs := new(big.Int).Exp(ka.g, ka.xOurs, ka.p)
512 // http://tools.ietf.org/html/rfc5246#section-7.4.3
513 pBytes := ka.p.Bytes()
514 gBytes := ka.g.Bytes()
515 yBytes := yOurs.Bytes()
516 serverDHParams := make([]byte, 0, 2+len(pBytes)+2+len(gBytes)+2+len(yBytes))
517 serverDHParams = append(serverDHParams, byte(len(pBytes)>>8), byte(len(pBytes)))
518 serverDHParams = append(serverDHParams, pBytes...)
519 serverDHParams = append(serverDHParams, byte(len(gBytes)>>8), byte(len(gBytes)))
520 serverDHParams = append(serverDHParams, gBytes...)
521 serverDHParams = append(serverDHParams, byte(len(yBytes)>>8), byte(len(yBytes)))
522 serverDHParams = append(serverDHParams, yBytes...)
524 return ka.auth.signParameters(config, cert, clientHello, hello, serverDHParams)
527 func (ka *dheKeyAgreement) processClientKeyExchange(config *Config, cert *Certificate, ckx *clientKeyExchangeMsg, version uint16) ([]byte, error) {
528 if len(ckx.ciphertext) < 2 {
529 return nil, errClientKeyExchange
531 yLen := (int(ckx.ciphertext[0]) << 8) | int(ckx.ciphertext[1])
532 if yLen != len(ckx.ciphertext)-2 {
533 return nil, errClientKeyExchange
535 yTheirs := new(big.Int).SetBytes(ckx.ciphertext[2:])
536 if yTheirs.Sign() <= 0 || yTheirs.Cmp(ka.p) >= 0 {
537 return nil, errClientKeyExchange
539 return new(big.Int).Exp(yTheirs, ka.xOurs, ka.p).Bytes(), nil
542 func (ka *dheKeyAgreement) processServerKeyExchange(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, skx *serverKeyExchangeMsg) error {
546 return errServerKeyExchange
548 pLen := (int(k[0]) << 8) | int(k[1])
551 return errServerKeyExchange
553 ka.p = new(big.Int).SetBytes(k[:pLen])
558 return errServerKeyExchange
560 gLen := (int(k[0]) << 8) | int(k[1])
563 return errServerKeyExchange
565 ka.g = new(big.Int).SetBytes(k[:gLen])
570 return errServerKeyExchange
572 yLen := (int(k[0]) << 8) | int(k[1])
575 return errServerKeyExchange
577 ka.yTheirs = new(big.Int).SetBytes(k[:yLen])
579 if ka.yTheirs.Sign() <= 0 || ka.yTheirs.Cmp(ka.p) >= 0 {
580 return errServerKeyExchange
584 serverDHParams := skx.key[:len(skx.key)-len(sig)]
586 return ka.auth.verifyParameters(config, clientHello, serverHello, cert, serverDHParams, sig)
589 func (ka *dheKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, error) {
590 if ka.p == nil || ka.g == nil || ka.yTheirs == nil {
591 return nil, nil, errors.New("missing ServerKeyExchange message")
594 xOurs, err := rand.Int(config.rand(), ka.p)
598 preMasterSecret := new(big.Int).Exp(ka.yTheirs, xOurs, ka.p).Bytes()
600 yOurs := new(big.Int).Exp(ka.g, xOurs, ka.p)
601 yBytes := yOurs.Bytes()
602 ckx := new(clientKeyExchangeMsg)
603 ckx.ciphertext = make([]byte, 2+len(yBytes))
604 ckx.ciphertext[0] = byte(len(yBytes) >> 8)
605 ckx.ciphertext[1] = byte(len(yBytes))
606 copy(ckx.ciphertext[2:], yBytes)
608 return preMasterSecret, ckx, nil
611 // nilKeyAgreement is a fake key agreement used to implement the plain PSK key
613 type nilKeyAgreement struct{}
615 func (ka *nilKeyAgreement) generateServerKeyExchange(config *Config, cert *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg) (*serverKeyExchangeMsg, error) {
619 func (ka *nilKeyAgreement) processClientKeyExchange(config *Config, cert *Certificate, ckx *clientKeyExchangeMsg, version uint16) ([]byte, error) {
620 if len(ckx.ciphertext) != 0 {
621 return nil, errClientKeyExchange
624 // Although in plain PSK, otherSecret is all zeros, the base key
625 // agreement does not access to the length of the pre-shared
626 // key. pskKeyAgreement instead interprets nil to mean to use all zeros
627 // of the appropriate length.
631 func (ka *nilKeyAgreement) processServerKeyExchange(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, skx *serverKeyExchangeMsg) error {
632 if len(skx.key) != 0 {
633 return errServerKeyExchange
638 func (ka *nilKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, error) {
639 // Although in plain PSK, otherSecret is all zeros, the base key
640 // agreement does not access to the length of the pre-shared
641 // key. pskKeyAgreement instead interprets nil to mean to use all zeros
642 // of the appropriate length.
643 return nil, &clientKeyExchangeMsg{}, nil
646 // makePSKPremaster formats a PSK pre-master secret based on otherSecret from
647 // the base key exchange and psk.
648 func makePSKPremaster(otherSecret, psk []byte) []byte {
649 out := make([]byte, 0, 2+len(otherSecret)+2+len(psk))
650 out = append(out, byte(len(otherSecret)>>8), byte(len(otherSecret)))
651 out = append(out, otherSecret...)
652 out = append(out, byte(len(psk)>>8), byte(len(psk)))
653 out = append(out, psk...)
657 // pskKeyAgreement implements the PSK key agreement.
658 type pskKeyAgreement struct {
663 func (ka *pskKeyAgreement) generateServerKeyExchange(config *Config, cert *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg) (*serverKeyExchangeMsg, error) {
664 // Assemble the identity hint.
665 bytes := make([]byte, 2+len(config.PreSharedKeyIdentity))
666 bytes[0] = byte(len(config.PreSharedKeyIdentity) >> 8)
667 bytes[1] = byte(len(config.PreSharedKeyIdentity))
668 copy(bytes[2:], []byte(config.PreSharedKeyIdentity))
670 // If there is one, append the base key agreement's
671 // ServerKeyExchange.
672 baseSkx, err := ka.base.generateServerKeyExchange(config, cert, clientHello, hello)
678 bytes = append(bytes, baseSkx.key...)
679 } else if config.PreSharedKeyIdentity == "" {
680 // ServerKeyExchange is optional if the identity hint is empty
681 // and there would otherwise be no ServerKeyExchange.
685 skx := new(serverKeyExchangeMsg)
690 func (ka *pskKeyAgreement) processClientKeyExchange(config *Config, cert *Certificate, ckx *clientKeyExchangeMsg, version uint16) ([]byte, error) {
691 // First, process the PSK identity.
692 if len(ckx.ciphertext) < 2 {
693 return nil, errClientKeyExchange
695 identityLen := (int(ckx.ciphertext[0]) << 8) | int(ckx.ciphertext[1])
696 if 2+identityLen > len(ckx.ciphertext) {
697 return nil, errClientKeyExchange
699 identity := string(ckx.ciphertext[2 : 2+identityLen])
701 if identity != config.PreSharedKeyIdentity {
702 return nil, errors.New("tls: unexpected identity")
705 if config.PreSharedKey == nil {
706 return nil, errors.New("tls: pre-shared key not configured")
709 // Process the remainder of the ClientKeyExchange to compute the base
710 // pre-master secret.
711 newCkx := new(clientKeyExchangeMsg)
712 newCkx.ciphertext = ckx.ciphertext[2+identityLen:]
713 otherSecret, err := ka.base.processClientKeyExchange(config, cert, newCkx, version)
718 if otherSecret == nil {
719 // Special-case for the plain PSK key exchanges.
720 otherSecret = make([]byte, len(config.PreSharedKey))
722 return makePSKPremaster(otherSecret, config.PreSharedKey), nil
725 func (ka *pskKeyAgreement) processServerKeyExchange(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, skx *serverKeyExchangeMsg) error {
726 if len(skx.key) < 2 {
727 return errServerKeyExchange
729 identityLen := (int(skx.key[0]) << 8) | int(skx.key[1])
730 if 2+identityLen > len(skx.key) {
731 return errServerKeyExchange
733 ka.identityHint = string(skx.key[2 : 2+identityLen])
735 // Process the remainder of the ServerKeyExchange.
736 newSkx := new(serverKeyExchangeMsg)
737 newSkx.key = skx.key[2+identityLen:]
738 return ka.base.processServerKeyExchange(config, clientHello, serverHello, cert, newSkx)
741 func (ka *pskKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, error) {
742 // The server only sends an identity hint but, for purposes of
743 // test code, the server always sends the hint and it is
744 // required to match.
745 if ka.identityHint != config.PreSharedKeyIdentity {
746 return nil, nil, errors.New("tls: unexpected identity")
749 // Serialize the identity.
750 bytes := make([]byte, 2+len(config.PreSharedKeyIdentity))
751 bytes[0] = byte(len(config.PreSharedKeyIdentity) >> 8)
752 bytes[1] = byte(len(config.PreSharedKeyIdentity))
753 copy(bytes[2:], []byte(config.PreSharedKeyIdentity))
755 // Append the base key exchange's ClientKeyExchange.
756 otherSecret, baseCkx, err := ka.base.generateClientKeyExchange(config, clientHello, cert)
760 ckx := new(clientKeyExchangeMsg)
761 ckx.ciphertext = append(bytes, baseCkx.ciphertext...)
763 if config.PreSharedKey == nil {
764 return nil, nil, errors.New("tls: pre-shared key not configured")
766 if otherSecret == nil {
767 otherSecret = make([]byte, len(config.PreSharedKey))
769 return makePSKPremaster(otherSecret, config.PreSharedKey), ckx, nil