prf.go

     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  const (
    78  	masterSecretLength   = 48 // Length of a master secret in TLS 1.1.
    79  	finishedVerifyLength = 12 // Length of verify_data in a Finished message.
    80  )
    81  
    82  var masterSecretLabel = []byte("master secret")
    83  var extendedMasterSecretLabel = []byte("extended master secret")
    84  var keyExpansionLabel = []byte("key expansion")
    85  var clientFinishedLabel = []byte("client finished")
    86  var serverFinishedLabel = []byte("server finished")
    87  
    88  func prfAndHashForVersion(version uint16, suite *cipherSuite) (func(result, secret, label, seed []byte), crypto.Hash) {
    89  	switch version {
    90  	case VersionTLS10, VersionTLS11:
    91  		return prf10, crypto.Hash(0)
    92  	case VersionTLS12:
    93  		if suite.flags&suiteSHA384 != 0 {
    94  			return prf12(sha512.New384), crypto.SHA384
    95  		}
    96  		return prf12(sha256.New), crypto.SHA256
    97  	default:
    98  		panic("unknown version")
    99  	}
   100  }
   101  
   102  func prfForVersion(version uint16, suite *cipherSuite) func(result, secret, label, seed []byte) {
   103  	prf, _ := prfAndHashForVersion(version, suite)
   104  	return prf
   105  }
   106  
   107  // masterFromPreMasterSecret generates the master secret from the pre-master
   108  // secret. See RFC 5246, Section 8.1.
   109  func masterFromPreMasterSecret(version uint16, suite *cipherSuite, preMasterSecret, clientRandom, serverRandom []byte) []byte {
   110  	seed := make([]byte, 0, len(clientRandom)+len(serverRandom))
   111  	seed = append(seed, clientRandom...)
   112  	seed = append(seed, serverRandom...)
   113  
   114  	masterSecret := make([]byte, masterSecretLength)
   115  	prfForVersion(version, suite)(masterSecret, preMasterSecret, masterSecretLabel, seed)
   116  	return masterSecret
   117  }
   118  
   119  // extMasterFromPreMasterSecret generates the extended master secret from the
   120  // pre-master secret. See RFC 7627.
   121  func extMasterFromPreMasterSecret(version uint16, suite *cipherSuite, preMasterSecret, transcript []byte) []byte {
   122  	masterSecret := make([]byte, masterSecretLength)
   123  	prfForVersion(version, suite)(masterSecret, preMasterSecret, extendedMasterSecretLabel, transcript)
   124  	return masterSecret
   125  }
   126  
   127  // keysFromMasterSecret generates the connection keys from the master
   128  // secret, given the lengths of the MAC key, cipher key and IV, as defined in
   129  // RFC 2246, Section 6.3.
   130  func keysFromMasterSecret(version uint16, suite *cipherSuite, masterSecret, clientRandom, serverRandom []byte, macLen, keyLen, ivLen int) (clientMAC, serverMAC, clientKey, serverKey, clientIV, serverIV []byte) {
   131  	seed := make([]byte, 0, len(serverRandom)+len(clientRandom))
   132  	seed = append(seed, serverRandom...)
   133  	seed = append(seed, clientRandom...)
   134  
   135  	n := 2*macLen + 2*keyLen + 2*ivLen
   136  	keyMaterial := make([]byte, n)
   137  	prfForVersion(version, suite)(keyMaterial, masterSecret, keyExpansionLabel, seed)
   138  	clientMAC = keyMaterial[:macLen]
   139  	keyMaterial = keyMaterial[macLen:]
   140  	serverMAC = keyMaterial[:macLen]
   141  	keyMaterial = keyMaterial[macLen:]
   142  	clientKey = keyMaterial[:keyLen]
   143  	keyMaterial = keyMaterial[keyLen:]
   144  	serverKey = keyMaterial[:keyLen]
   145  	keyMaterial = keyMaterial[keyLen:]
   146  	clientIV = keyMaterial[:ivLen]
   147  	keyMaterial = keyMaterial[ivLen:]
   148  	serverIV = keyMaterial[:ivLen]
   149  	return
   150  }
   151  
   152  func newFinishedHash(version uint16, cipherSuite *cipherSuite) finishedHash {
   153  	var buffer []byte
   154  	if version >= VersionTLS12 {
   155  		buffer = []byte{}
   156  	}
   157  
   158  	prf, hash := prfAndHashForVersion(version, cipherSuite)
   159  	if hash != 0 {
   160  		return finishedHash{hash.New(), hash.New(), nil, nil, buffer, version, prf}
   161  	}
   162  
   163  	return finishedHash{sha1.New(), sha1.New(), md5.New(), md5.New(), buffer, version, prf}
   164  }
   165  
   166  // A finishedHash calculates the hash of a set of handshake messages suitable
   167  // for including in a Finished message.
   168  type finishedHash struct {
   169  	client hash.Hash
   170  	server hash.Hash
   171  
   172  	// Prior to TLS 1.2, an additional MD5 hash is required.
   173  	clientMD5 hash.Hash
   174  	serverMD5 hash.Hash
   175  
   176  	// In TLS 1.2, a full buffer is sadly required.
   177  	buffer []byte
   178  
   179  	version uint16
   180  	prf     func(result, secret, label, seed []byte)
   181  }
   182  
   183  func (h *finishedHash) Write(msg []byte) (n int, err error) {
   184  	h.client.Write(msg)
   185  	h.server.Write(msg)
   186  
   187  	if h.version < VersionTLS12 {
   188  		h.clientMD5.Write(msg)
   189  		h.serverMD5.Write(msg)
   190  	}
   191  
   192  	if h.buffer != nil {
   193  		h.buffer = append(h.buffer, msg...)
   194  	}
   195  
   196  	return len(msg), nil
   197  }
   198  
   199  func (h finishedHash) Sum() []byte {
   200  	if h.version >= VersionTLS12 {
   201  		return h.client.Sum(nil)
   202  	}
   203  
   204  	out := make([]byte, 0, md5.Size+sha1.Size)
   205  	out = h.clientMD5.Sum(out)
   206  	return h.client.Sum(out)
   207  }
   208  
   209  // clientSum returns the contents of the verify_data member of a client's
   210  // Finished message.
   211  func (h finishedHash) clientSum(masterSecret []byte) []byte {
   212  	out := make([]byte, finishedVerifyLength)
   213  	h.prf(out, masterSecret, clientFinishedLabel, h.Sum())
   214  	return out
   215  }
   216  
   217  // serverSum returns the contents of the verify_data member of a server's
   218  // Finished message.
   219  func (h finishedHash) serverSum(masterSecret []byte) []byte {
   220  	out := make([]byte, finishedVerifyLength)
   221  	h.prf(out, masterSecret, serverFinishedLabel, h.Sum())
   222  	return out
   223  }
   224  
   225  // hashForClientCertificate returns the handshake messages so far, pre-hashed if
   226  // necessary, suitable for signing by a TLS client certificate.
   227  func (h finishedHash) hashForClientCertificate(sigType uint8, hashAlg crypto.Hash) []byte {
   228  	if (h.version >= VersionTLS12 || sigType == signatureEd25519) && h.buffer == nil {
   229  		panic("tls: handshake hash for a client certificate requested after discarding the handshake buffer")
   230  	}
   231  
   232  	if sigType == signatureEd25519 {
   233  		return h.buffer
   234  	}
   235  
   236  	if h.version >= VersionTLS12 {
   237  		hash := hashAlg.New()
   238  		hash.Write(h.buffer)
   239  		return hash.Sum(nil)
   240  	}
   241  
   242  	if sigType == signatureECDSA {
   243  		return h.server.Sum(nil)
   244  	}
   245  
   246  	return h.Sum()
   247  }
   248  
   249  // discardHandshakeBuffer is called when there is no more need to
   250  // buffer the entirety of the handshake messages.
   251  func (h *finishedHash) discardHandshakeBuffer() {
   252  	h.buffer = nil
   253  }
   254  
   255  // noEKMBecauseRenegotiation is used as a value of
   256  // ConnectionState.ekm when renegotiation is enabled and thus
   257  // we wish to fail all key-material export requests.
   258  func noEKMBecauseRenegotiation(label string, context []byte, length int) ([]byte, error) {
   259  	return nil, errors.New("crypto/tls: ExportKeyingMaterial is unavailable when renegotiation is enabled")
   260  }
   261  
   262  // noEKMBecauseNoEMS is used as a value of ConnectionState.ekm when Extended
   263  // Master Secret is not negotiated and thus we wish to fail all key-material
   264  // export requests.
   265  func noEKMBecauseNoEMS(label string, context []byte, length int) ([]byte, error) {
   266  	return nil, errors.New("crypto/tls: ExportKeyingMaterial is unavailable when neither TLS 1.3 nor Extended Master Secret are negotiated; override with GODEBUG=tlsunsafeekm=1")
   267  }
   268  
   269  // ekmFromMasterSecret generates exported keying material as defined in RFC 5705.
   270  func ekmFromMasterSecret(version uint16, suite *cipherSuite, masterSecret, clientRandom, serverRandom []byte) func(string, []byte, int) ([]byte, error) {
   271  	return func(label string, context []byte, length int) ([]byte, error) {
   272  		switch label {
   273  		case "client finished", "server finished", "master secret", "key expansion":
   274  			// These values are reserved and may not be used.
   275  			return nil, fmt.Errorf("crypto/tls: reserved ExportKeyingMaterial label: %s", label)
   276  		}
   277  
   278  		seedLen := len(serverRandom) + len(clientRandom)
   279  		if context != nil {
   280  			seedLen += 2 + len(context)
   281  		}
   282  		seed := make([]byte, 0, seedLen)
   283  
   284  		seed = append(seed, clientRandom...)
   285  		seed = append(seed, serverRandom...)
   286  
   287  		if context != nil {
   288  			if len(context) >= 1<<16 {
   289  				return nil, fmt.Errorf("crypto/tls: ExportKeyingMaterial context too long")
   290  			}
   291  			seed = append(seed, byte(len(context)>>8), byte(len(context)))
   292  			seed = append(seed, context...)
   293  		}
   294  
   295  		keyMaterial := make([]byte, length)
   296  		prfForVersion(version, suite)(keyMaterial, masterSecret, []byte(label), seed)
   297  		return keyMaterial, nil
   298  	}
   299  }
   300
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