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 sigAndHash argument is 114 // only used for >= TLS 1.2 and precisely identifies the hash function to use. 115 func hashForServerKeyExchange(sigAndHash signatureAndHash, version uint16, slices ...[]byte) ([]byte, crypto.Hash, error) { 116 if version >= VersionTLS12 { 117 if !isSupportedSignatureAndHash(sigAndHash, supportedSignatureAlgorithms) { 118 return nil, crypto.Hash(0), errors.New("tls: unsupported hash function used by peer") 119 } 120 hashFunc, err := lookupTLSHash(sigAndHash.hash) 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 sigAndHash.signature == 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 []signatureAndHash) (uint8, 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 return hashSHA1, nil 146 } 147 148 for _, sigAndHash := range clientList { 149 if sigAndHash.signature != sigType { 150 continue 151 } 152 if isSupportedSignatureAndHash(sigAndHash, supportedSignatureAlgorithms) { 153 return sigAndHash.hash, nil 154 } 155 } 156 157 return 0, errors.New("tls: client doesn't support any common hash functions") 158 } 159 160 func curveForCurveID(id CurveID) (elliptic.Curve, bool) { 161 switch id { 162 case CurveP256: 163 return elliptic.P256(), true 164 case CurveP384: 165 return elliptic.P384(), true 166 case CurveP521: 167 return elliptic.P521(), true 168 default: 169 return nil, false 170 } 171 172 } 173 174 // ecdheRSAKeyAgreement implements a TLS key agreement where the server 175 // generates a ephemeral EC public/private key pair and signs it. The 176 // pre-master secret is then calculated using ECDH. The signature may 177 // either be ECDSA or RSA. 178 type ecdheKeyAgreement struct { 179 version uint16 180 sigType uint8 181 privateKey []byte 182 curveid CurveID 183 184 // publicKey is used to store the peer's public value when X25519 is 185 // being used. 186 publicKey []byte 187 // x and y are used to store the peer's public value when one of the 188 // NIST curves is being used. 189 x, y *big.Int 190 } 191 192 func (ka *ecdheKeyAgreement) generateServerKeyExchange(config *Config, cert *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg) (*serverKeyExchangeMsg, error) { 193 preferredCurves := config.curvePreferences() 194 195 NextCandidate: 196 for _, candidate := range preferredCurves { 197 for _, c := range clientHello.supportedCurves { 198 if candidate == c { 199 ka.curveid = c 200 break NextCandidate 201 } 202 } 203 } 204 205 if ka.curveid == 0 { 206 return nil, errors.New("tls: no supported elliptic curves offered") 207 } 208 209 var ecdhePublic []byte 210 211 if ka.curveid == X25519 { 212 var scalar, public [32]byte 213 if _, err := io.ReadFull(config.rand(), scalar[:]); err != nil { 214 return nil, err 215 } 216 217 curve25519.ScalarBaseMult(&public, &scalar) 218 ka.privateKey = scalar[:] 219 ecdhePublic = public[:] 220 } else { 221 curve, ok := curveForCurveID(ka.curveid) 222 if !ok { 223 return nil, errors.New("tls: preferredCurves includes unsupported curve") 224 } 225 226 var x, y *big.Int 227 var err error 228 ka.privateKey, x, y, err = elliptic.GenerateKey(curve, config.rand()) 229 if err != nil { 230 return nil, err 231 } 232 ecdhePublic = elliptic.Marshal(curve, x, y) 233 } 234 235 // http://tools.ietf.org/html/rfc4492#section-5.4 236 serverECDHParams := make([]byte, 1+2+1+len(ecdhePublic)) 237 serverECDHParams[0] = 3 // named curve 238 serverECDHParams[1] = byte(ka.curveid >> 8) 239 serverECDHParams[2] = byte(ka.curveid) 240 serverECDHParams[3] = byte(len(ecdhePublic)) 241 copy(serverECDHParams[4:], ecdhePublic) 242 243 sigAndHash := signatureAndHash{signature: ka.sigType} 244 245 if ka.version >= VersionTLS12 { 246 var err error 247 if sigAndHash.hash, err = pickTLS12HashForSignature(ka.sigType, clientHello.signatureAndHashes); err != nil { 248 return nil, err 249 } 250 } 251 252 digest, hashFunc, err := hashForServerKeyExchange(sigAndHash, ka.version, clientHello.random, hello.random, serverECDHParams) 253 if err != nil { 254 return nil, err 255 } 256 257 priv, ok := cert.PrivateKey.(crypto.Signer) 258 if !ok { 259 return nil, errors.New("tls: certificate private key does not implement crypto.Signer") 260 } 261 var sig []byte 262 switch ka.sigType { 263 case signatureECDSA: 264 _, ok := priv.Public().(*ecdsa.PublicKey) 265 if !ok { 266 return nil, errors.New("tls: ECDHE ECDSA requires an ECDSA server key") 267 } 268 case signatureRSA: 269 _, ok := priv.Public().(*rsa.PublicKey) 270 if !ok { 271 return nil, errors.New("tls: ECDHE RSA requires a RSA server key") 272 } 273 default: 274 return nil, errors.New("tls: unknown ECDHE signature algorithm") 275 } 276 sig, err = priv.Sign(config.rand(), digest, hashFunc) 277 if err != nil { 278 return nil, errors.New("tls: failed to sign ECDHE parameters: " + err.Error()) 279 } 280 281 skx := new(serverKeyExchangeMsg) 282 sigAndHashLen := 0 283 if ka.version >= VersionTLS12 { 284 sigAndHashLen = 2 285 } 286 skx.key = make([]byte, len(serverECDHParams)+sigAndHashLen+2+len(sig)) 287 copy(skx.key, serverECDHParams) 288 k := skx.key[len(serverECDHParams):] 289 if ka.version >= VersionTLS12 { 290 k[0] = sigAndHash.hash 291 k[1] = sigAndHash.signature 292 k = k[2:] 293 } 294 k[0] = byte(len(sig) >> 8) 295 k[1] = byte(len(sig)) 296 copy(k[2:], sig) 297 298 return skx, nil 299 } 300 301 func (ka *ecdheKeyAgreement) processClientKeyExchange(config *Config, cert *Certificate, ckx *clientKeyExchangeMsg, version uint16) ([]byte, error) { 302 if len(ckx.ciphertext) == 0 || int(ckx.ciphertext[0]) != len(ckx.ciphertext)-1 { 303 return nil, errClientKeyExchange 304 } 305 306 if ka.curveid == X25519 { 307 if len(ckx.ciphertext) != 1+32 { 308 return nil, errClientKeyExchange 309 } 310 311 var theirPublic, sharedKey, scalar [32]byte 312 copy(theirPublic[:], ckx.ciphertext[1:]) 313 copy(scalar[:], ka.privateKey) 314 curve25519.ScalarMult(&sharedKey, &scalar, &theirPublic) 315 return sharedKey[:], nil 316 } 317 318 curve, ok := curveForCurveID(ka.curveid) 319 if !ok { 320 panic("internal error") 321 } 322 x, y := elliptic.Unmarshal(curve, ckx.ciphertext[1:]) 323 if x == nil { 324 return nil, errClientKeyExchange 325 } 326 if !curve.IsOnCurve(x, y) { 327 return nil, errClientKeyExchange 328 } 329 x, _ = curve.ScalarMult(x, y, ka.privateKey) 330 preMasterSecret := make([]byte, (curve.Params().BitSize+7)>>3) 331 xBytes := x.Bytes() 332 copy(preMasterSecret[len(preMasterSecret)-len(xBytes):], xBytes) 333 334 return preMasterSecret, nil 335 } 336 337 func (ka *ecdheKeyAgreement) processServerKeyExchange(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, skx *serverKeyExchangeMsg) error { 338 if len(skx.key) < 4 { 339 return errServerKeyExchange 340 } 341 if skx.key[0] != 3 { // named curve 342 return errors.New("tls: server selected unsupported curve") 343 } 344 ka.curveid = CurveID(skx.key[1])<<8 | CurveID(skx.key[2]) 345 346 publicLen := int(skx.key[3]) 347 if publicLen+4 > len(skx.key) { 348 return errServerKeyExchange 349 } 350 serverECDHParams := skx.key[:4+publicLen] 351 publicKey := serverECDHParams[4:] 352 353 sig := skx.key[4+publicLen:] 354 if len(sig) < 2 { 355 return errServerKeyExchange 356 } 357 358 if ka.curveid == X25519 { 359 if len(publicKey) != 32 { 360 return errors.New("tls: bad X25519 public value") 361 } 362 ka.publicKey = publicKey 363 } else { 364 curve, ok := curveForCurveID(ka.curveid) 365 if !ok { 366 return errors.New("tls: server selected unsupported curve") 367 } 368 369 ka.x, ka.y = elliptic.Unmarshal(curve, publicKey) 370 if ka.x == nil { 371 return errServerKeyExchange 372 } 373 if !curve.IsOnCurve(ka.x, ka.y) { 374 return errServerKeyExchange 375 } 376 } 377 378 sigAndHash := signatureAndHash{signature: ka.sigType} 379 if ka.version >= VersionTLS12 { 380 // handle SignatureAndHashAlgorithm 381 sigAndHash = signatureAndHash{hash: sig[0], signature: sig[1]} 382 if sigAndHash.signature != ka.sigType { 383 return errServerKeyExchange 384 } 385 sig = sig[2:] 386 if len(sig) < 2 { 387 return errServerKeyExchange 388 } 389 } 390 sigLen := int(sig[0])<<8 | int(sig[1]) 391 if sigLen+2 != len(sig) { 392 return errServerKeyExchange 393 } 394 sig = sig[2:] 395 396 digest, hashFunc, err := hashForServerKeyExchange(sigAndHash, ka.version, clientHello.random, serverHello.random, serverECDHParams) 397 if err != nil { 398 return err 399 } 400 switch ka.sigType { 401 case signatureECDSA: 402 pubKey, ok := cert.PublicKey.(*ecdsa.PublicKey) 403 if !ok { 404 return errors.New("tls: ECDHE ECDSA requires a ECDSA server public key") 405 } 406 ecdsaSig := new(ecdsaSignature) 407 if _, err := asn1.Unmarshal(sig, ecdsaSig); err != nil { 408 return err 409 } 410 if ecdsaSig.R.Sign() <= 0 || ecdsaSig.S.Sign() <= 0 { 411 return errors.New("tls: ECDSA signature contained zero or negative values") 412 } 413 if !ecdsa.Verify(pubKey, digest, ecdsaSig.R, ecdsaSig.S) { 414 return errors.New("tls: ECDSA verification failure") 415 } 416 case signatureRSA: 417 pubKey, ok := cert.PublicKey.(*rsa.PublicKey) 418 if !ok { 419 return errors.New("tls: ECDHE RSA requires a RSA server public key") 420 } 421 if err := rsa.VerifyPKCS1v15(pubKey, hashFunc, digest, sig); err != nil { 422 return err 423 } 424 default: 425 return errors.New("tls: unknown ECDHE signature algorithm") 426 } 427 428 return nil 429 } 430 431 func (ka *ecdheKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, error) { 432 if ka.curveid == 0 { 433 return nil, nil, errors.New("tls: missing ServerKeyExchange message") 434 } 435 436 var serialized, preMasterSecret []byte 437 438 if ka.curveid == X25519 { 439 var ourPublic, theirPublic, sharedKey, scalar [32]byte 440 441 if _, err := io.ReadFull(config.rand(), scalar[:]); err != nil { 442 return nil, nil, err 443 } 444 445 copy(theirPublic[:], ka.publicKey) 446 curve25519.ScalarBaseMult(&ourPublic, &scalar) 447 curve25519.ScalarMult(&sharedKey, &scalar, &theirPublic) 448 serialized = ourPublic[:] 449 preMasterSecret = sharedKey[:] 450 } else { 451 curve, ok := curveForCurveID(ka.curveid) 452 if !ok { 453 panic("internal error") 454 } 455 priv, mx, my, err := elliptic.GenerateKey(curve, config.rand()) 456 if err != nil { 457 return nil, nil, err 458 } 459 x, _ := curve.ScalarMult(ka.x, ka.y, priv) 460 preMasterSecret = make([]byte, (curve.Params().BitSize+7)>>3) 461 xBytes := x.Bytes() 462 copy(preMasterSecret[len(preMasterSecret)-len(xBytes):], xBytes) 463 464 serialized = elliptic.Marshal(curve, mx, my) 465 } 466 467 ckx := new(clientKeyExchangeMsg) 468 ckx.ciphertext = make([]byte, 1+len(serialized)) 469 ckx.ciphertext[0] = byte(len(serialized)) 470 copy(ckx.ciphertext[1:], serialized) 471 472 return preMasterSecret, ckx, nil 473 } 474
