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  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 keyExpansionLabel = []byte("key expansion")
    84  var clientFinishedLabel = []byte("client finished")
    85  var serverFinishedLabel = []byte("server finished")
    86  
    87  func prfAndHashForVersion(version uint16, suite *cipherSuite) (func(result, secret, label, seed []byte), crypto.Hash) {
    88  	switch version {
    89  	case VersionTLS10, VersionTLS11:
    90  		return prf10, crypto.Hash(0)
    91  	case VersionTLS12:
    92  		if suite.flags&suiteSHA384 != 0 {
    93  			return prf12(sha512.New384), crypto.SHA384
    94  		}
    95  		return prf12(sha256.New), crypto.SHA256
    96  	default:
    97  		panic("unknown version")
    98  	}
    99  }
   100  
   101  func prfForVersion(version uint16, suite *cipherSuite) func(result, secret, label, seed []byte) {
   102  	prf, _ := prfAndHashForVersion(version, suite)
   103  	return prf
   104  }
   105  
   106  // masterFromPreMasterSecret generates the master secret from the pre-master
   107  // secret. See RFC 5246, Section 8.1.
   108  func masterFromPreMasterSecret(version uint16, suite *cipherSuite, preMasterSecret, clientRandom, serverRandom []byte) []byte {
   109  	seed := make([]byte, 0, len(clientRandom)+len(serverRandom))
   110  	seed = append(seed, clientRandom...)
   111  	seed = append(seed, serverRandom...)
   112  
   113  	masterSecret := make([]byte, masterSecretLength)
   114  	prfForVersion(version, suite)(masterSecret, preMasterSecret, masterSecretLabel, seed)
   115  	return masterSecret
   116  }
   117  
   118  // keysFromMasterSecret generates the connection keys from the master
   119  // secret, given the lengths of the MAC key, cipher key and IV, as defined in
   120  // RFC 2246, Section 6.3.
   121  func keysFromMasterSecret(version uint16, suite *cipherSuite, masterSecret, clientRandom, serverRandom []byte, macLen, keyLen, ivLen int) (clientMAC, serverMAC, clientKey, serverKey, clientIV, serverIV []byte) {
   122  	seed := make([]byte, 0, len(serverRandom)+len(clientRandom))
   123  	seed = append(seed, serverRandom...)
   124  	seed = append(seed, clientRandom...)
   125  
   126  	n := 2*macLen + 2*keyLen + 2*ivLen
   127  	keyMaterial := make([]byte, n)
   128  	prfForVersion(version, suite)(keyMaterial, masterSecret, keyExpansionLabel, seed)
   129  	clientMAC = keyMaterial[:macLen]
   130  	keyMaterial = keyMaterial[macLen:]
   131  	serverMAC = keyMaterial[:macLen]
   132  	keyMaterial = keyMaterial[macLen:]
   133  	clientKey = keyMaterial[:keyLen]
   134  	keyMaterial = keyMaterial[keyLen:]
   135  	serverKey = keyMaterial[:keyLen]
   136  	keyMaterial = keyMaterial[keyLen:]
   137  	clientIV = keyMaterial[:ivLen]
   138  	keyMaterial = keyMaterial[ivLen:]
   139  	serverIV = keyMaterial[:ivLen]
   140  	return
   141  }
   142  
   143  func newFinishedHash(version uint16, cipherSuite *cipherSuite) finishedHash {
   144  	var buffer []byte
   145  	if version >= VersionTLS12 {
   146  		buffer = []byte{}
   147  	}
   148  
   149  	prf, hash := prfAndHashForVersion(version, cipherSuite)
   150  	if hash != 0 {
   151  		return finishedHash{hash.New(), hash.New(), nil, nil, buffer, version, prf}
   152  	}
   153  
   154  	return finishedHash{sha1.New(), sha1.New(), md5.New(), md5.New(), buffer, version, prf}
   155  }
   156  
   157  // A finishedHash calculates the hash of a set of handshake messages suitable
   158  // for including in a Finished message.
   159  type finishedHash struct {
   160  	client hash.Hash
   161  	server hash.Hash
   162  
   163  	// Prior to TLS 1.2, an additional MD5 hash is required.
   164  	clientMD5 hash.Hash
   165  	serverMD5 hash.Hash
   166  
   167  	// In TLS 1.2, a full buffer is sadly required.
   168  	buffer []byte
   169  
   170  	version uint16
   171  	prf     func(result, secret, label, seed []byte)
   172  }
   173  
   174  func (h *finishedHash) Write(msg []byte) (n int, err error) {
   175  	h.client.Write(msg)
   176  	h.server.Write(msg)
   177  
   178  	if h.version < VersionTLS12 {
   179  		h.clientMD5.Write(msg)
   180  		h.serverMD5.Write(msg)
   181  	}
   182  
   183  	if h.buffer != nil {
   184  		h.buffer = append(h.buffer, msg...)
   185  	}
   186  
   187  	return len(msg), nil
   188  }
   189  
   190  func (h finishedHash) Sum() []byte {
   191  	if h.version >= VersionTLS12 {
   192  		return h.client.Sum(nil)
   193  	}
   194  
   195  	out := make([]byte, 0, md5.Size+sha1.Size)
   196  	out = h.clientMD5.Sum(out)
   197  	return h.client.Sum(out)
   198  }
   199  
   200  // clientSum returns the contents of the verify_data member of a client's
   201  // Finished message.
   202  func (h finishedHash) clientSum(masterSecret []byte) []byte {
   203  	out := make([]byte, finishedVerifyLength)
   204  	h.prf(out, masterSecret, clientFinishedLabel, h.Sum())
   205  	return out
   206  }
   207  
   208  // serverSum returns the contents of the verify_data member of a server's
   209  // Finished message.
   210  func (h finishedHash) serverSum(masterSecret []byte) []byte {
   211  	out := make([]byte, finishedVerifyLength)
   212  	h.prf(out, masterSecret, serverFinishedLabel, h.Sum())
   213  	return out
   214  }
   215  
   216  // hashForClientCertificate returns the handshake messages so far, pre-hashed if
   217  // necessary, suitable for signing by a TLS client certificate.
   218  func (h finishedHash) hashForClientCertificate(sigType uint8, hashAlg crypto.Hash, masterSecret []byte) []byte {
   219  	if (h.version >= VersionTLS12 || sigType == signatureEd25519) && h.buffer == nil {
   220  		panic("tls: handshake hash for a client certificate requested after discarding the handshake buffer")
   221  	}
   222  
   223  	if sigType == signatureEd25519 {
   224  		return h.buffer
   225  	}
   226  
   227  	if h.version >= VersionTLS12 {
   228  		hash := hashAlg.New()
   229  		hash.Write(h.buffer)
   230  		return hash.Sum(nil)
   231  	}
   232  
   233  	if sigType == signatureECDSA {
   234  		return h.server.Sum(nil)
   235  	}
   236  
   237  	return h.Sum()
   238  }
   239  
   240  // discardHandshakeBuffer is called when there is no more need to
   241  // buffer the entirety of the handshake messages.
   242  func (h *finishedHash) discardHandshakeBuffer() {
   243  	h.buffer = nil
   244  }
   245  
   246  // noExportedKeyingMaterial is used as a value of
   247  // ConnectionState.ekm when renegotiation is enabled and thus
   248  // we wish to fail all key-material export requests.
   249  func noExportedKeyingMaterial(label string, context []byte, length int) ([]byte, error) {
   250  	return nil, errors.New("crypto/tls: ExportKeyingMaterial is unavailable when renegotiation is enabled")
   251  }
   252  
   253  // ekmFromMasterSecret generates exported keying material as defined in RFC 5705.
   254  func ekmFromMasterSecret(version uint16, suite *cipherSuite, masterSecret, clientRandom, serverRandom []byte) func(string, []byte, int) ([]byte, error) {
   255  	return func(label string, context []byte, length int) ([]byte, error) {
   256  		switch label {
   257  		case "client finished", "server finished", "master secret", "key expansion":
   258  			// These values are reserved and may not be used.
   259  			return nil, fmt.Errorf("crypto/tls: reserved ExportKeyingMaterial label: %s", label)
   260  		}
   261  
   262  		seedLen := len(serverRandom) + len(clientRandom)
   263  		if context != nil {
   264  			seedLen += 2 + len(context)
   265  		}
   266  		seed := make([]byte, 0, seedLen)
   267  
   268  		seed = append(seed, clientRandom...)
   269  		seed = append(seed, serverRandom...)
   270  
   271  		if context != nil {
   272  			if len(context) >= 1<<16 {
   273  				return nil, fmt.Errorf("crypto/tls: ExportKeyingMaterial context too long")
   274  			}
   275  			seed = append(seed, byte(len(context)>>8), byte(len(context)))
   276  			seed = append(seed, context...)
   277  		}
   278  
   279  		keyMaterial := make([]byte, length)
   280  		prfForVersion(version, suite)(keyMaterial, masterSecret, []byte(label), seed)
   281  		return keyMaterial, nil
   282  	}
   283  }
   284  

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