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. 4 5 package tls 6 7 import ( 8 "crypto" 9 "crypto/ecdsa" 10 "crypto/elliptic" 11 "crypto/md5" 12 "crypto/rsa" 13 "crypto/sha1" 14 "crypto/x509" 15 "encoding/asn1" 16 "errors" 17 "io" 18 "math/big" 19 20 "golang_org/x/crypto/curve25519" 21 ) 22 23 var errClientKeyExchange = errors.New("tls: invalid ClientKeyExchange message") 24 var errServerKeyExchange = errors.New("tls: invalid ServerKeyExchange message") 25 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{} 29 30 func (ka rsaKeyAgreement) generateServerKeyExchange(config *Config, cert *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg) (*serverKeyExchangeMsg, error) { 31 return nil, nil 32 } 33 34 func (ka rsaKeyAgreement) processClientKeyExchange(config *Config, cert *Certificate, ckx *clientKeyExchangeMsg, version uint16) ([]byte, error) { 35 if len(ckx.ciphertext) < 2 { 36 return nil, errClientKeyExchange 37 } 38 39 ciphertext := ckx.ciphertext 40 if version != VersionSSL30 { 41 ciphertextLen := int(ckx.ciphertext[0])<<8 | int(ckx.ciphertext[1]) 42 if ciphertextLen != len(ckx.ciphertext)-2 { 43 return nil, errClientKeyExchange 44 } 45 ciphertext = ckx.ciphertext[2:] 46 } 47 priv, ok := cert.PrivateKey.(crypto.Decrypter) 48 if !ok { 49 return nil, errors.New("tls: certificate private key does not implement crypto.Decrypter") 50 } 51 // Perform constant time RSA PKCS#1 v1.5 decryption 52 preMasterSecret, err := priv.Decrypt(config.rand(), ciphertext, &rsa.PKCS1v15DecryptOptions{SessionKeyLen: 48}) 53 if err != nil { 54 return nil, err 55 } 56 // We don't check the version number in the premaster secret. For one, 57 // by checking it, we would leak information about the validity of the 58 // encrypted pre-master secret. Secondly, it provides only a small 59 // benefit against a downgrade attack and some implementations send the 60 // wrong version anyway. See the discussion at the end of section 61 // 7.4.7.1 of RFC 4346. 62 return preMasterSecret, nil 63 } 64 65 func (ka rsaKeyAgreement) processServerKeyExchange(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, skx *serverKeyExchangeMsg) error { 66 return errors.New("tls: unexpected ServerKeyExchange") 67 } 68 69 func (ka rsaKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, error) { 70 preMasterSecret := make([]byte, 48) 71 preMasterSecret[0] = byte(clientHello.vers >> 8) 72 preMasterSecret[1] = byte(clientHello.vers) 73 _, err := io.ReadFull(config.rand(), preMasterSecret[2:]) 74 if err != nil { 75 return nil, nil, err 76 } 77 78 encrypted, err := rsa.EncryptPKCS1v15(config.rand(), cert.PublicKey.(*rsa.PublicKey), preMasterSecret) 79 if err != nil { 80 return nil, nil, err 81 } 82 ckx := new(clientKeyExchangeMsg) 83 ckx.ciphertext = make([]byte, len(encrypted)+2) 84 ckx.ciphertext[0] = byte(len(encrypted) >> 8) 85 ckx.ciphertext[1] = byte(len(encrypted)) 86 copy(ckx.ciphertext[2:], encrypted) 87 return preMasterSecret, ckx, nil 88 } 89 90 // sha1Hash calculates a SHA1 hash over the given byte slices. 91 func sha1Hash(slices [][]byte) []byte { 92 hsha1 := sha1.New() 93 for _, slice := range slices { 94 hsha1.Write(slice) 95 } 96 return hsha1.Sum(nil) 97 } 98 99 // md5SHA1Hash implements TLS 1.0's hybrid hash function which consists of the 100 // concatenation of an MD5 and SHA1 hash. 101 func md5SHA1Hash(slices [][]byte) []byte { 102 md5sha1 := make([]byte, md5.Size+sha1.Size) 103 hmd5 := md5.New() 104 for _, slice := range slices { 105 hmd5.Write(slice) 106 } 107 copy(md5sha1, hmd5.Sum(nil)) 108 copy(md5sha1[md5.Size:], sha1Hash(slices)) 109 return md5sha1 110 } 111 112 // hashForServerKeyExchange hashes the given slices and returns their digest 113 // and the identifier of the hash function used. The signatureAlgorithm argument 114 // is only used for >= TLS 1.2 and identifies the hash function to use. 115 func hashForServerKeyExchange(sigType uint8, signatureAlgorithm SignatureScheme, version uint16, slices ...[]byte) ([]byte, crypto.Hash, error) { 116 if version >= VersionTLS12 { 117 if !isSupportedSignatureAlgorithm(signatureAlgorithm, supportedSignatureAlgorithms) { 118 return nil, crypto.Hash(0), errors.New("tls: unsupported hash function used by peer") 119 } 120 hashFunc, err := lookupTLSHash(signatureAlgorithm) 121 if err != nil { 122 return nil, crypto.Hash(0), err 123 } 124 h := hashFunc.New() 125 for _, slice := range slices { 126 h.Write(slice) 127 } 128 digest := h.Sum(nil) 129 return digest, hashFunc, nil 130 } 131 if sigType == signatureECDSA { 132 return sha1Hash(slices), crypto.SHA1, nil 133 } 134 return md5SHA1Hash(slices), crypto.MD5SHA1, nil 135 } 136 137 // pickTLS12HashForSignature returns a TLS 1.2 hash identifier for signing a 138 // ServerKeyExchange given the signature type being used and the client's 139 // advertised list of supported signature and hash combinations. 140 func pickTLS12HashForSignature(sigType uint8, clientList []SignatureScheme) (SignatureScheme, error) { 141 if len(clientList) == 0 { 142 // If the client didn't specify any signature_algorithms 143 // extension then we can assume that it supports SHA1. See 144 // http://tools.ietf.org/html/rfc5246#section-7.4.1.4.1 145 switch sigType { 146 case signatureRSA: 147 return PKCS1WithSHA1, nil 148 case signatureECDSA: 149 return ECDSAWithSHA1, nil 150 default: 151 return 0, errors.New("tls: unknown signature algorithm") 152 } 153 } 154 155 for _, sigAlg := range clientList { 156 if signatureFromSignatureScheme(sigAlg) != sigType { 157 continue 158 } 159 if isSupportedSignatureAlgorithm(sigAlg, supportedSignatureAlgorithms) { 160 return sigAlg, nil 161 } 162 } 163 164 return 0, errors.New("tls: client doesn't support any common hash functions") 165 } 166 167 func curveForCurveID(id CurveID) (elliptic.Curve, bool) { 168 switch id { 169 case CurveP256: 170 return elliptic.P256(), true 171 case CurveP384: 172 return elliptic.P384(), true 173 case CurveP521: 174 return elliptic.P521(), true 175 default: 176 return nil, false 177 } 178 179 } 180 181 // ecdheRSAKeyAgreement implements a TLS key agreement where the server 182 // generates an ephemeral EC public/private key pair and signs it. The 183 // pre-master secret is then calculated using ECDH. The signature may 184 // either be ECDSA or RSA. 185 type ecdheKeyAgreement struct { 186 version uint16 187 sigType uint8 188 privateKey []byte 189 curveid CurveID 190 191 // publicKey is used to store the peer's public value when X25519 is 192 // being used. 193 publicKey []byte 194 // x and y are used to store the peer's public value when one of the 195 // NIST curves is being used. 196 x, y *big.Int 197 } 198 199 func (ka *ecdheKeyAgreement) generateServerKeyExchange(config *Config, cert *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg) (*serverKeyExchangeMsg, error) { 200 preferredCurves := config.curvePreferences() 201 202 NextCandidate: 203 for _, candidate := range preferredCurves { 204 for _, c := range clientHello.supportedCurves { 205 if candidate == c { 206 ka.curveid = c 207 break NextCandidate 208 } 209 } 210 } 211 212 if ka.curveid == 0 { 213 return nil, errors.New("tls: no supported elliptic curves offered") 214 } 215 216 var ecdhePublic []byte 217 218 if ka.curveid == X25519 { 219 var scalar, public [32]byte 220 if _, err := io.ReadFull(config.rand(), scalar[:]); err != nil { 221 return nil, err 222 } 223 224 curve25519.ScalarBaseMult(&public, &scalar) 225 ka.privateKey = scalar[:] 226 ecdhePublic = public[:] 227 } else { 228 curve, ok := curveForCurveID(ka.curveid) 229 if !ok { 230 return nil, errors.New("tls: preferredCurves includes unsupported curve") 231 } 232 233 var x, y *big.Int 234 var err error 235 ka.privateKey, x, y, err = elliptic.GenerateKey(curve, config.rand()) 236 if err != nil { 237 return nil, err 238 } 239 ecdhePublic = elliptic.Marshal(curve, x, y) 240 } 241 242 // http://tools.ietf.org/html/rfc4492#section-5.4 243 serverECDHParams := make([]byte, 1+2+1+len(ecdhePublic)) 244 serverECDHParams[0] = 3 // named curve 245 serverECDHParams[1] = byte(ka.curveid >> 8) 246 serverECDHParams[2] = byte(ka.curveid) 247 serverECDHParams[3] = byte(len(ecdhePublic)) 248 copy(serverECDHParams[4:], ecdhePublic) 249 250 var signatureAlgorithm SignatureScheme 251 252 if ka.version >= VersionTLS12 { 253 var err error 254 signatureAlgorithm, err = pickTLS12HashForSignature(ka.sigType, clientHello.supportedSignatureAlgorithms) 255 if err != nil { 256 return nil, err 257 } 258 } 259 260 digest, hashFunc, err := hashForServerKeyExchange(ka.sigType, signatureAlgorithm, ka.version, clientHello.random, hello.random, serverECDHParams) 261 if err != nil { 262 return nil, err 263 } 264 265 priv, ok := cert.PrivateKey.(crypto.Signer) 266 if !ok { 267 return nil, errors.New("tls: certificate private key does not implement crypto.Signer") 268 } 269 var sig []byte 270 switch ka.sigType { 271 case signatureECDSA: 272 _, ok := priv.Public().(*ecdsa.PublicKey) 273 if !ok { 274 return nil, errors.New("tls: ECDHE ECDSA requires an ECDSA server key") 275 } 276 case signatureRSA: 277 _, ok := priv.Public().(*rsa.PublicKey) 278 if !ok { 279 return nil, errors.New("tls: ECDHE RSA requires a RSA server key") 280 } 281 default: 282 return nil, errors.New("tls: unknown ECDHE signature algorithm") 283 } 284 sig, err = priv.Sign(config.rand(), digest, hashFunc) 285 if err != nil { 286 return nil, errors.New("tls: failed to sign ECDHE parameters: " + err.Error()) 287 } 288 289 skx := new(serverKeyExchangeMsg) 290 sigAndHashLen := 0 291 if ka.version >= VersionTLS12 { 292 sigAndHashLen = 2 293 } 294 skx.key = make([]byte, len(serverECDHParams)+sigAndHashLen+2+len(sig)) 295 copy(skx.key, serverECDHParams) 296 k := skx.key[len(serverECDHParams):] 297 if ka.version >= VersionTLS12 { 298 k[0] = byte(signatureAlgorithm >> 8) 299 k[1] = byte(signatureAlgorithm) 300 k = k[2:] 301 } 302 k[0] = byte(len(sig) >> 8) 303 k[1] = byte(len(sig)) 304 copy(k[2:], sig) 305 306 return skx, nil 307 } 308 309 func (ka *ecdheKeyAgreement) processClientKeyExchange(config *Config, cert *Certificate, ckx *clientKeyExchangeMsg, version uint16) ([]byte, error) { 310 if len(ckx.ciphertext) == 0 || int(ckx.ciphertext[0]) != len(ckx.ciphertext)-1 { 311 return nil, errClientKeyExchange 312 } 313 314 if ka.curveid == X25519 { 315 if len(ckx.ciphertext) != 1+32 { 316 return nil, errClientKeyExchange 317 } 318 319 var theirPublic, sharedKey, scalar [32]byte 320 copy(theirPublic[:], ckx.ciphertext[1:]) 321 copy(scalar[:], ka.privateKey) 322 curve25519.ScalarMult(&sharedKey, &scalar, &theirPublic) 323 return sharedKey[:], nil 324 } 325 326 curve, ok := curveForCurveID(ka.curveid) 327 if !ok { 328 panic("internal error") 329 } 330 x, y := elliptic.Unmarshal(curve, ckx.ciphertext[1:]) // Unmarshal also checks whether the given point is on the curve 331 if x == nil { 332 return nil, errClientKeyExchange 333 } 334 x, _ = curve.ScalarMult(x, y, ka.privateKey) 335 preMasterSecret := make([]byte, (curve.Params().BitSize+7)>>3) 336 xBytes := x.Bytes() 337 copy(preMasterSecret[len(preMasterSecret)-len(xBytes):], xBytes) 338 339 return preMasterSecret, nil 340 } 341 342 func (ka *ecdheKeyAgreement) processServerKeyExchange(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, skx *serverKeyExchangeMsg) error { 343 if len(skx.key) < 4 { 344 return errServerKeyExchange 345 } 346 if skx.key[0] != 3 { // named curve 347 return errors.New("tls: server selected unsupported curve") 348 } 349 ka.curveid = CurveID(skx.key[1])<<8 | CurveID(skx.key[2]) 350 351 publicLen := int(skx.key[3]) 352 if publicLen+4 > len(skx.key) { 353 return errServerKeyExchange 354 } 355 serverECDHParams := skx.key[:4+publicLen] 356 publicKey := serverECDHParams[4:] 357 358 sig := skx.key[4+publicLen:] 359 if len(sig) < 2 { 360 return errServerKeyExchange 361 } 362 363 if ka.curveid == X25519 { 364 if len(publicKey) != 32 { 365 return errors.New("tls: bad X25519 public value") 366 } 367 ka.publicKey = publicKey 368 } else { 369 curve, ok := curveForCurveID(ka.curveid) 370 if !ok { 371 return errors.New("tls: server selected unsupported curve") 372 } 373 ka.x, ka.y = elliptic.Unmarshal(curve, publicKey) // Unmarshal also checks whether the given point is on the curve 374 if ka.x == nil { 375 return errServerKeyExchange 376 } 377 } 378 379 var signatureAlgorithm SignatureScheme 380 if ka.version >= VersionTLS12 { 381 // handle SignatureAndHashAlgorithm 382 signatureAlgorithm = SignatureScheme(sig[0])<<8 | SignatureScheme(sig[1]) 383 if signatureFromSignatureScheme(signatureAlgorithm) != ka.sigType { 384 return errServerKeyExchange 385 } 386 sig = sig[2:] 387 if len(sig) < 2 { 388 return errServerKeyExchange 389 } 390 } 391 sigLen := int(sig[0])<<8 | int(sig[1]) 392 if sigLen+2 != len(sig) { 393 return errServerKeyExchange 394 } 395 sig = sig[2:] 396 397 digest, hashFunc, err := hashForServerKeyExchange(ka.sigType, signatureAlgorithm, ka.version, clientHello.random, serverHello.random, serverECDHParams) 398 if err != nil { 399 return err 400 } 401 switch ka.sigType { 402 case signatureECDSA: 403 pubKey, ok := cert.PublicKey.(*ecdsa.PublicKey) 404 if !ok { 405 return errors.New("tls: ECDHE ECDSA requires a ECDSA server public key") 406 } 407 ecdsaSig := new(ecdsaSignature) 408 if _, err := asn1.Unmarshal(sig, ecdsaSig); err != nil { 409 return err 410 } 411 if ecdsaSig.R.Sign() <= 0 || ecdsaSig.S.Sign() <= 0 { 412 return errors.New("tls: ECDSA signature contained zero or negative values") 413 } 414 if !ecdsa.Verify(pubKey, digest, ecdsaSig.R, ecdsaSig.S) { 415 return errors.New("tls: ECDSA verification failure") 416 } 417 case signatureRSA: 418 pubKey, ok := cert.PublicKey.(*rsa.PublicKey) 419 if !ok { 420 return errors.New("tls: ECDHE RSA requires a RSA server public key") 421 } 422 if err := rsa.VerifyPKCS1v15(pubKey, hashFunc, digest, sig); err != nil { 423 return err 424 } 425 default: 426 return errors.New("tls: unknown ECDHE signature algorithm") 427 } 428 429 return nil 430 } 431 432 func (ka *ecdheKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, error) { 433 if ka.curveid == 0 { 434 return nil, nil, errors.New("tls: missing ServerKeyExchange message") 435 } 436 437 var serialized, preMasterSecret []byte 438 439 if ka.curveid == X25519 { 440 var ourPublic, theirPublic, sharedKey, scalar [32]byte 441 442 if _, err := io.ReadFull(config.rand(), scalar[:]); err != nil { 443 return nil, nil, err 444 } 445 446 copy(theirPublic[:], ka.publicKey) 447 curve25519.ScalarBaseMult(&ourPublic, &scalar) 448 curve25519.ScalarMult(&sharedKey, &scalar, &theirPublic) 449 serialized = ourPublic[:] 450 preMasterSecret = sharedKey[:] 451 } else { 452 curve, ok := curveForCurveID(ka.curveid) 453 if !ok { 454 panic("internal error") 455 } 456 priv, mx, my, err := elliptic.GenerateKey(curve, config.rand()) 457 if err != nil { 458 return nil, nil, err 459 } 460 x, _ := curve.ScalarMult(ka.x, ka.y, priv) 461 preMasterSecret = make([]byte, (curve.Params().BitSize+7)>>3) 462 xBytes := x.Bytes() 463 copy(preMasterSecret[len(preMasterSecret)-len(xBytes):], xBytes) 464 465 serialized = elliptic.Marshal(curve, mx, my) 466 } 467 468 ckx := new(clientKeyExchangeMsg) 469 ckx.ciphertext = make([]byte, 1+len(serialized)) 470 ckx.ciphertext[0] = byte(len(serialized)) 471 copy(ckx.ciphertext[1:], serialized) 472 473 return preMasterSecret, ckx, nil 474 } 475
