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Source file src/crypto/tls/prf.go

Documentation: crypto/tls

     1  // Copyright 2009 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/hmac"
    10  	"crypto/md5"
    11  	"crypto/sha1"
    12  	"crypto/sha256"
    13  	"crypto/sha512"
    14  	"errors"
    15  	"fmt"
    16  	"hash"
    17  )
    18  
    19  // Split a premaster secret in two as specified in RFC 4346, Section 5.
    20  func splitPreMasterSecret(secret []byte) (s1, s2 []byte) {
    21  	s1 = secret[0 : (len(secret)+1)/2]
    22  	s2 = secret[len(secret)/2:]
    23  	return
    24  }
    25  
    26  // pHash implements the P_hash function, as defined in RFC 4346, Section 5.
    27  func pHash(result, secret, seed []byte, hash func() hash.Hash) {
    28  	h := hmac.New(hash, secret)
    29  	h.Write(seed)
    30  	a := h.Sum(nil)
    31  
    32  	j := 0
    33  	for j < len(result) {
    34  		h.Reset()
    35  		h.Write(a)
    36  		h.Write(seed)
    37  		b := h.Sum(nil)
    38  		copy(result[j:], b)
    39  		j += len(b)
    40  
    41  		h.Reset()
    42  		h.Write(a)
    43  		a = h.Sum(nil)
    44  	}
    45  }
    46  
    47  // prf10 implements the TLS 1.0 pseudo-random function, as defined in RFC 2246, Section 5.
    48  func prf10(result, secret, label, seed []byte) {
    49  	hashSHA1 := sha1.New
    50  	hashMD5 := md5.New
    51  
    52  	labelAndSeed := make([]byte, len(label)+len(seed))
    53  	copy(labelAndSeed, label)
    54  	copy(labelAndSeed[len(label):], seed)
    55  
    56  	s1, s2 := splitPreMasterSecret(secret)
    57  	pHash(result, s1, labelAndSeed, hashMD5)
    58  	result2 := make([]byte, len(result))
    59  	pHash(result2, s2, labelAndSeed, hashSHA1)
    60  
    61  	for i, b := range result2 {
    62  		result[i] ^= b
    63  	}
    64  }
    65  
    66  // prf12 implements the TLS 1.2 pseudo-random function, as defined in RFC 5246, Section 5.
    67  func prf12(hashFunc func() hash.Hash) func(result, secret, label, seed []byte) {
    68  	return func(result, secret, label, seed []byte) {
    69  		labelAndSeed := make([]byte, len(label)+len(seed))
    70  		copy(labelAndSeed, label)
    71  		copy(labelAndSeed[len(label):], seed)
    72  
    73  		pHash(result, secret, labelAndSeed, hashFunc)
    74  	}
    75  }
    76  
    77  // prf30 implements the SSL 3.0 pseudo-random function, as defined in
    78  // www.mozilla.org/projects/security/pki/nss/ssl/draft302.txt section 6.
    79  func prf30(result, secret, label, seed []byte) {
    80  	hashSHA1 := sha1.New()
    81  	hashMD5 := md5.New()
    82  
    83  	done := 0
    84  	i := 0
    85  	// RFC 5246 section 6.3 says that the largest PRF output needed is 128
    86  	// bytes. Since no more ciphersuites will be added to SSLv3, this will
    87  	// remain true. Each iteration gives us 16 bytes so 10 iterations will
    88  	// be sufficient.
    89  	var b [11]byte
    90  	for done < len(result) {
    91  		for j := 0; j <= i; j++ {
    92  			b[j] = 'A' + byte(i)
    93  		}
    94  
    95  		hashSHA1.Reset()
    96  		hashSHA1.Write(b[:i+1])
    97  		hashSHA1.Write(secret)
    98  		hashSHA1.Write(seed)
    99  		digest := hashSHA1.Sum(nil)
   100  
   101  		hashMD5.Reset()
   102  		hashMD5.Write(secret)
   103  		hashMD5.Write(digest)
   104  
   105  		done += copy(result[done:], hashMD5.Sum(nil))
   106  		i++
   107  	}
   108  }
   109  
   110  const (
   111  	masterSecretLength   = 48 // Length of a master secret in TLS 1.1.
   112  	finishedVerifyLength = 12 // Length of verify_data in a Finished message.
   113  )
   114  
   115  var masterSecretLabel = []byte("master secret")
   116  var keyExpansionLabel = []byte("key expansion")
   117  var clientFinishedLabel = []byte("client finished")
   118  var serverFinishedLabel = []byte("server finished")
   119  
   120  func prfAndHashForVersion(version uint16, suite *cipherSuite) (func(result, secret, label, seed []byte), crypto.Hash) {
   121  	switch version {
   122  	case VersionSSL30:
   123  		return prf30, crypto.Hash(0)
   124  	case VersionTLS10, VersionTLS11:
   125  		return prf10, crypto.Hash(0)
   126  	case VersionTLS12:
   127  		if suite.flags&suiteSHA384 != 0 {
   128  			return prf12(sha512.New384), crypto.SHA384
   129  		}
   130  		return prf12(sha256.New), crypto.SHA256
   131  	default:
   132  		panic("unknown version")
   133  	}
   134  }
   135  
   136  func prfForVersion(version uint16, suite *cipherSuite) func(result, secret, label, seed []byte) {
   137  	prf, _ := prfAndHashForVersion(version, suite)
   138  	return prf
   139  }
   140  
   141  // masterFromPreMasterSecret generates the master secret from the pre-master
   142  // secret. See RFC 5246, Section 8.1.
   143  func masterFromPreMasterSecret(version uint16, suite *cipherSuite, preMasterSecret, clientRandom, serverRandom []byte) []byte {
   144  	seed := make([]byte, 0, len(clientRandom)+len(serverRandom))
   145  	seed = append(seed, clientRandom...)
   146  	seed = append(seed, serverRandom...)
   147  
   148  	masterSecret := make([]byte, masterSecretLength)
   149  	prfForVersion(version, suite)(masterSecret, preMasterSecret, masterSecretLabel, seed)
   150  	return masterSecret
   151  }
   152  
   153  // keysFromMasterSecret generates the connection keys from the master
   154  // secret, given the lengths of the MAC key, cipher key and IV, as defined in
   155  // RFC 2246, Section 6.3.
   156  func keysFromMasterSecret(version uint16, suite *cipherSuite, masterSecret, clientRandom, serverRandom []byte, macLen, keyLen, ivLen int) (clientMAC, serverMAC, clientKey, serverKey, clientIV, serverIV []byte) {
   157  	seed := make([]byte, 0, len(serverRandom)+len(clientRandom))
   158  	seed = append(seed, serverRandom...)
   159  	seed = append(seed, clientRandom...)
   160  
   161  	n := 2*macLen + 2*keyLen + 2*ivLen
   162  	keyMaterial := make([]byte, n)
   163  	prfForVersion(version, suite)(keyMaterial, masterSecret, keyExpansionLabel, seed)
   164  	clientMAC = keyMaterial[:macLen]
   165  	keyMaterial = keyMaterial[macLen:]
   166  	serverMAC = keyMaterial[:macLen]
   167  	keyMaterial = keyMaterial[macLen:]
   168  	clientKey = keyMaterial[:keyLen]
   169  	keyMaterial = keyMaterial[keyLen:]
   170  	serverKey = keyMaterial[:keyLen]
   171  	keyMaterial = keyMaterial[keyLen:]
   172  	clientIV = keyMaterial[:ivLen]
   173  	keyMaterial = keyMaterial[ivLen:]
   174  	serverIV = keyMaterial[:ivLen]
   175  	return
   176  }
   177  
   178  // hashFromSignatureScheme returns the corresponding crypto.Hash for a given
   179  // hash from a TLS SignatureScheme.
   180  func hashFromSignatureScheme(signatureAlgorithm SignatureScheme) (crypto.Hash, error) {
   181  	switch signatureAlgorithm {
   182  	case PKCS1WithSHA1, ECDSAWithSHA1:
   183  		return crypto.SHA1, nil
   184  	case PKCS1WithSHA256, PSSWithSHA256, ECDSAWithP256AndSHA256:
   185  		return crypto.SHA256, nil
   186  	case PKCS1WithSHA384, PSSWithSHA384, ECDSAWithP384AndSHA384:
   187  		return crypto.SHA384, nil
   188  	case PKCS1WithSHA512, PSSWithSHA512, ECDSAWithP521AndSHA512:
   189  		return crypto.SHA512, nil
   190  	default:
   191  		return 0, fmt.Errorf("tls: unsupported signature algorithm: %#04x", signatureAlgorithm)
   192  	}
   193  }
   194  
   195  func newFinishedHash(version uint16, cipherSuite *cipherSuite) finishedHash {
   196  	var buffer []byte
   197  	if version == VersionSSL30 || version >= VersionTLS12 {
   198  		buffer = []byte{}
   199  	}
   200  
   201  	prf, hash := prfAndHashForVersion(version, cipherSuite)
   202  	if hash != 0 {
   203  		return finishedHash{hash.New(), hash.New(), nil, nil, buffer, version, prf}
   204  	}
   205  
   206  	return finishedHash{sha1.New(), sha1.New(), md5.New(), md5.New(), buffer, version, prf}
   207  }
   208  
   209  // A finishedHash calculates the hash of a set of handshake messages suitable
   210  // for including in a Finished message.
   211  type finishedHash struct {
   212  	client hash.Hash
   213  	server hash.Hash
   214  
   215  	// Prior to TLS 1.2, an additional MD5 hash is required.
   216  	clientMD5 hash.Hash
   217  	serverMD5 hash.Hash
   218  
   219  	// In TLS 1.2, a full buffer is sadly required.
   220  	buffer []byte
   221  
   222  	version uint16
   223  	prf     func(result, secret, label, seed []byte)
   224  }
   225  
   226  func (h *finishedHash) Write(msg []byte) (n int, err error) {
   227  	h.client.Write(msg)
   228  	h.server.Write(msg)
   229  
   230  	if h.version < VersionTLS12 {
   231  		h.clientMD5.Write(msg)
   232  		h.serverMD5.Write(msg)
   233  	}
   234  
   235  	if h.buffer != nil {
   236  		h.buffer = append(h.buffer, msg...)
   237  	}
   238  
   239  	return len(msg), nil
   240  }
   241  
   242  func (h finishedHash) Sum() []byte {
   243  	if h.version >= VersionTLS12 {
   244  		return h.client.Sum(nil)
   245  	}
   246  
   247  	out := make([]byte, 0, md5.Size+sha1.Size)
   248  	out = h.clientMD5.Sum(out)
   249  	return h.client.Sum(out)
   250  }
   251  
   252  // finishedSum30 calculates the contents of the verify_data member of a SSLv3
   253  // Finished message given the MD5 and SHA1 hashes of a set of handshake
   254  // messages.
   255  func finishedSum30(md5, sha1 hash.Hash, masterSecret []byte, magic []byte) []byte {
   256  	md5.Write(magic)
   257  	md5.Write(masterSecret)
   258  	md5.Write(ssl30Pad1[:])
   259  	md5Digest := md5.Sum(nil)
   260  
   261  	md5.Reset()
   262  	md5.Write(masterSecret)
   263  	md5.Write(ssl30Pad2[:])
   264  	md5.Write(md5Digest)
   265  	md5Digest = md5.Sum(nil)
   266  
   267  	sha1.Write(magic)
   268  	sha1.Write(masterSecret)
   269  	sha1.Write(ssl30Pad1[:40])
   270  	sha1Digest := sha1.Sum(nil)
   271  
   272  	sha1.Reset()
   273  	sha1.Write(masterSecret)
   274  	sha1.Write(ssl30Pad2[:40])
   275  	sha1.Write(sha1Digest)
   276  	sha1Digest = sha1.Sum(nil)
   277  
   278  	ret := make([]byte, len(md5Digest)+len(sha1Digest))
   279  	copy(ret, md5Digest)
   280  	copy(ret[len(md5Digest):], sha1Digest)
   281  	return ret
   282  }
   283  
   284  var ssl3ClientFinishedMagic = [4]byte{0x43, 0x4c, 0x4e, 0x54}
   285  var ssl3ServerFinishedMagic = [4]byte{0x53, 0x52, 0x56, 0x52}
   286  
   287  // clientSum returns the contents of the verify_data member of a client's
   288  // Finished message.
   289  func (h finishedHash) clientSum(masterSecret []byte) []byte {
   290  	if h.version == VersionSSL30 {
   291  		return finishedSum30(h.clientMD5, h.client, masterSecret, ssl3ClientFinishedMagic[:])
   292  	}
   293  
   294  	out := make([]byte, finishedVerifyLength)
   295  	h.prf(out, masterSecret, clientFinishedLabel, h.Sum())
   296  	return out
   297  }
   298  
   299  // serverSum returns the contents of the verify_data member of a server's
   300  // Finished message.
   301  func (h finishedHash) serverSum(masterSecret []byte) []byte {
   302  	if h.version == VersionSSL30 {
   303  		return finishedSum30(h.serverMD5, h.server, masterSecret, ssl3ServerFinishedMagic[:])
   304  	}
   305  
   306  	out := make([]byte, finishedVerifyLength)
   307  	h.prf(out, masterSecret, serverFinishedLabel, h.Sum())
   308  	return out
   309  }
   310  
   311  // hashForClientCertificate returns a digest over the handshake messages so far,
   312  // suitable for signing by a TLS client certificate.
   313  func (h finishedHash) hashForClientCertificate(sigType uint8, hashAlg crypto.Hash, masterSecret []byte) ([]byte, error) {
   314  	if (h.version == VersionSSL30 || h.version >= VersionTLS12) && h.buffer == nil {
   315  		panic("a handshake hash for a client-certificate was requested after discarding the handshake buffer")
   316  	}
   317  
   318  	if h.version == VersionSSL30 {
   319  		if sigType != signaturePKCS1v15 {
   320  			return nil, errors.New("tls: unsupported signature type for client certificate")
   321  		}
   322  
   323  		md5Hash := md5.New()
   324  		md5Hash.Write(h.buffer)
   325  		sha1Hash := sha1.New()
   326  		sha1Hash.Write(h.buffer)
   327  		return finishedSum30(md5Hash, sha1Hash, masterSecret, nil), nil
   328  	}
   329  	if h.version >= VersionTLS12 {
   330  		hash := hashAlg.New()
   331  		hash.Write(h.buffer)
   332  		return hash.Sum(nil), nil
   333  	}
   334  
   335  	if sigType == signatureECDSA {
   336  		return h.server.Sum(nil), nil
   337  	}
   338  
   339  	return h.Sum(), nil
   340  }
   341  
   342  // discardHandshakeBuffer is called when there is no more need to
   343  // buffer the entirety of the handshake messages.
   344  func (h *finishedHash) discardHandshakeBuffer() {
   345  	h.buffer = nil
   346  }
   347  
   348  // noExportedKeyingMaterial is used as a value of
   349  // ConnectionState.ekm when renegotation is enabled and thus
   350  // we wish to fail all key-material export requests.
   351  func noExportedKeyingMaterial(label string, context []byte, length int) ([]byte, error) {
   352  	return nil, errors.New("crypto/tls: ExportKeyingMaterial is unavailable when renegotiation is enabled")
   353  }
   354  
   355  // ekmFromMasterSecret generates exported keying material as defined in RFC 5705.
   356  func ekmFromMasterSecret(version uint16, suite *cipherSuite, masterSecret, clientRandom, serverRandom []byte) func(string, []byte, int) ([]byte, error) {
   357  	return func(label string, context []byte, length int) ([]byte, error) {
   358  		switch label {
   359  		case "client finished", "server finished", "master secret", "key expansion":
   360  			// These values are reserved and may not be used.
   361  			return nil, fmt.Errorf("crypto/tls: reserved ExportKeyingMaterial label: %s", label)
   362  		}
   363  
   364  		seedLen := len(serverRandom) + len(clientRandom)
   365  		if context != nil {
   366  			seedLen += 2 + len(context)
   367  		}
   368  		seed := make([]byte, 0, seedLen)
   369  
   370  		seed = append(seed, clientRandom...)
   371  		seed = append(seed, serverRandom...)
   372  
   373  		if context != nil {
   374  			if len(context) >= 1<<16 {
   375  				return nil, fmt.Errorf("crypto/tls: ExportKeyingMaterial context too long")
   376  			}
   377  			seed = append(seed, byte(len(context)>>8), byte(len(context)))
   378  			seed = append(seed, context...)
   379  		}
   380  
   381  		keyMaterial := make([]byte, length)
   382  		prfForVersion(version, suite)(keyMaterial, masterSecret, []byte(label), seed)
   383  		return keyMaterial, nil
   384  	}
   385  }
   386  

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