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/internal/fips140/tls12"
    11  	"crypto/md5"
    12  	"crypto/sha1"
    13  	"crypto/sha256"
    14  	"crypto/sha512"
    15  	"errors"
    16  	"fmt"
    17  	"hash"
    18  )
    19  
    20  type prfFunc func(secret []byte, label string, seed []byte, keyLen int) []byte
    21  
    22  // Split a premaster secret in two as specified in RFC 4346, Section 5.
    23  func splitPreMasterSecret(secret []byte) (s1, s2 []byte) {
    24  	s1 = secret[0 : (len(secret)+1)/2]
    25  	s2 = secret[len(secret)/2:]
    26  	return
    27  }
    28  
    29  // pHash implements the P_hash function, as defined in RFC 4346, Section 5.
    30  func pHash(result, secret, seed []byte, hash func() hash.Hash) {
    31  	h := hmac.New(hash, secret)
    32  	h.Write(seed)
    33  	a := h.Sum(nil)
    34  
    35  	j := 0
    36  	for j < len(result) {
    37  		h.Reset()
    38  		h.Write(a)
    39  		h.Write(seed)
    40  		b := h.Sum(nil)
    41  		copy(result[j:], b)
    42  		j += len(b)
    43  
    44  		h.Reset()
    45  		h.Write(a)
    46  		a = h.Sum(nil)
    47  	}
    48  }
    49  
    50  // prf10 implements the TLS 1.0 pseudo-random function, as defined in RFC 2246, Section 5.
    51  func prf10(secret []byte, label string, seed []byte, keyLen int) []byte {
    52  	result := make([]byte, keyLen)
    53  	hashSHA1 := sha1.New
    54  	hashMD5 := md5.New
    55  
    56  	labelAndSeed := make([]byte, len(label)+len(seed))
    57  	copy(labelAndSeed, label)
    58  	copy(labelAndSeed[len(label):], seed)
    59  
    60  	s1, s2 := splitPreMasterSecret(secret)
    61  	pHash(result, s1, labelAndSeed, hashMD5)
    62  	result2 := make([]byte, len(result))
    63  	pHash(result2, s2, labelAndSeed, hashSHA1)
    64  
    65  	for i, b := range result2 {
    66  		result[i] ^= b
    67  	}
    68  
    69  	return result
    70  }
    71  
    72  // prf12 implements the TLS 1.2 pseudo-random function, as defined in RFC 5246, Section 5.
    73  func prf12(hashFunc func() hash.Hash) prfFunc {
    74  	return func(secret []byte, label string, seed []byte, keyLen int) []byte {
    75  		return tls12.PRF(hashFunc, secret, label, seed, keyLen)
    76  	}
    77  }
    78  
    79  const (
    80  	masterSecretLength   = 48 // Length of a master secret in TLS 1.1.
    81  	finishedVerifyLength = 12 // Length of verify_data in a Finished message.
    82  )
    83  
    84  const masterSecretLabel = "master secret"
    85  const extendedMasterSecretLabel = "extended master secret"
    86  const keyExpansionLabel = "key expansion"
    87  const clientFinishedLabel = "client finished"
    88  const serverFinishedLabel = "server finished"
    89  
    90  func prfAndHashForVersion(version uint16, suite *cipherSuite) (prfFunc, crypto.Hash) {
    91  	switch version {
    92  	case VersionTLS10, VersionTLS11:
    93  		return prf10, crypto.Hash(0)
    94  	case VersionTLS12:
    95  		if suite.flags&suiteSHA384 != 0 {
    96  			return prf12(sha512.New384), crypto.SHA384
    97  		}
    98  		return prf12(sha256.New), crypto.SHA256
    99  	default:
   100  		panic("unknown version")
   101  	}
   102  }
   103  
   104  func prfForVersion(version uint16, suite *cipherSuite) prfFunc {
   105  	prf, _ := prfAndHashForVersion(version, suite)
   106  	return prf
   107  }
   108  
   109  // masterFromPreMasterSecret generates the master secret from the pre-master
   110  // secret. See RFC 5246, Section 8.1.
   111  func masterFromPreMasterSecret(version uint16, suite *cipherSuite, preMasterSecret, clientRandom, serverRandom []byte) []byte {
   112  	seed := make([]byte, 0, len(clientRandom)+len(serverRandom))
   113  	seed = append(seed, clientRandom...)
   114  	seed = append(seed, serverRandom...)
   115  
   116  	return prfForVersion(version, suite)(preMasterSecret, masterSecretLabel, seed, masterSecretLength)
   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  	prf, hash := prfAndHashForVersion(version, suite)
   123  	if version == VersionTLS12 {
   124  		// Use the FIPS 140-3 module only for TLS 1.2 with EMS, which is the
   125  		// only TLS 1.0-1.2 approved mode per IG D.Q.
   126  		return tls12.MasterSecret(hash.New, preMasterSecret, transcript)
   127  	}
   128  	return prf(preMasterSecret, extendedMasterSecretLabel, transcript, masterSecretLength)
   129  }
   130  
   131  // keysFromMasterSecret generates the connection keys from the master
   132  // secret, given the lengths of the MAC key, cipher key and IV, as defined in
   133  // RFC 2246, Section 6.3.
   134  func keysFromMasterSecret(version uint16, suite *cipherSuite, masterSecret, clientRandom, serverRandom []byte, macLen, keyLen, ivLen int) (clientMAC, serverMAC, clientKey, serverKey, clientIV, serverIV []byte) {
   135  	seed := make([]byte, 0, len(serverRandom)+len(clientRandom))
   136  	seed = append(seed, serverRandom...)
   137  	seed = append(seed, clientRandom...)
   138  
   139  	n := 2*macLen + 2*keyLen + 2*ivLen
   140  	keyMaterial := prfForVersion(version, suite)(masterSecret, keyExpansionLabel, seed, n)
   141  	clientMAC = keyMaterial[:macLen]
   142  	keyMaterial = keyMaterial[macLen:]
   143  	serverMAC = keyMaterial[:macLen]
   144  	keyMaterial = keyMaterial[macLen:]
   145  	clientKey = keyMaterial[:keyLen]
   146  	keyMaterial = keyMaterial[keyLen:]
   147  	serverKey = keyMaterial[:keyLen]
   148  	keyMaterial = keyMaterial[keyLen:]
   149  	clientIV = keyMaterial[:ivLen]
   150  	keyMaterial = keyMaterial[ivLen:]
   151  	serverIV = keyMaterial[:ivLen]
   152  	return
   153  }
   154  
   155  func newFinishedHash(version uint16, cipherSuite *cipherSuite) finishedHash {
   156  	var buffer []byte
   157  	if version >= VersionTLS12 {
   158  		buffer = []byte{}
   159  	}
   160  
   161  	prf, hash := prfAndHashForVersion(version, cipherSuite)
   162  	if hash != 0 {
   163  		return finishedHash{hash.New(), hash.New(), nil, nil, buffer, version, prf}
   164  	}
   165  
   166  	return finishedHash{sha1.New(), sha1.New(), md5.New(), md5.New(), buffer, version, prf}
   167  }
   168  
   169  // A finishedHash calculates the hash of a set of handshake messages suitable
   170  // for including in a Finished message.
   171  type finishedHash struct {
   172  	client hash.Hash
   173  	server hash.Hash
   174  
   175  	// Prior to TLS 1.2, an additional MD5 hash is required.
   176  	clientMD5 hash.Hash
   177  	serverMD5 hash.Hash
   178  
   179  	// In TLS 1.2, a full buffer is sadly required.
   180  	buffer []byte
   181  
   182  	version uint16
   183  	prf     prfFunc
   184  }
   185  
   186  func (h *finishedHash) Write(msg []byte) (n int, err error) {
   187  	h.client.Write(msg)
   188  	h.server.Write(msg)
   189  
   190  	if h.version < VersionTLS12 {
   191  		h.clientMD5.Write(msg)
   192  		h.serverMD5.Write(msg)
   193  	}
   194  
   195  	if h.buffer != nil {
   196  		h.buffer = append(h.buffer, msg...)
   197  	}
   198  
   199  	return len(msg), nil
   200  }
   201  
   202  func (h finishedHash) Sum() []byte {
   203  	if h.version >= VersionTLS12 {
   204  		return h.client.Sum(nil)
   205  	}
   206  
   207  	out := make([]byte, 0, md5.Size+sha1.Size)
   208  	out = h.clientMD5.Sum(out)
   209  	return h.client.Sum(out)
   210  }
   211  
   212  // clientSum returns the contents of the verify_data member of a client's
   213  // Finished message.
   214  func (h finishedHash) clientSum(masterSecret []byte) []byte {
   215  	return h.prf(masterSecret, clientFinishedLabel, h.Sum(), finishedVerifyLength)
   216  }
   217  
   218  // serverSum returns the contents of the verify_data member of a server's
   219  // Finished message.
   220  func (h finishedHash) serverSum(masterSecret []byte) []byte {
   221  	return h.prf(masterSecret, serverFinishedLabel, h.Sum(), finishedVerifyLength)
   222  }
   223  
   224  // hashForClientCertificate returns the handshake messages so far, pre-hashed if
   225  // necessary, suitable for signing by a TLS client certificate.
   226  func (h finishedHash) hashForClientCertificate(sigType uint8, hashAlg crypto.Hash) []byte {
   227  	if (h.version >= VersionTLS12 || sigType == signatureEd25519) && h.buffer == nil {
   228  		panic("tls: handshake hash for a client certificate requested after discarding the handshake buffer")
   229  	}
   230  
   231  	if sigType == signatureEd25519 {
   232  		return h.buffer
   233  	}
   234  
   235  	if h.version >= VersionTLS12 {
   236  		hash := hashAlg.New()
   237  		hash.Write(h.buffer)
   238  		return hash.Sum(nil)
   239  	}
   240  
   241  	if sigType == signatureECDSA {
   242  		return h.server.Sum(nil)
   243  	}
   244  
   245  	return h.Sum()
   246  }
   247  
   248  // discardHandshakeBuffer is called when there is no more need to
   249  // buffer the entirety of the handshake messages.
   250  func (h *finishedHash) discardHandshakeBuffer() {
   251  	h.buffer = nil
   252  }
   253  
   254  // noEKMBecauseRenegotiation is used as a value of
   255  // ConnectionState.ekm when renegotiation is enabled and thus
   256  // we wish to fail all key-material export requests.
   257  func noEKMBecauseRenegotiation(label string, context []byte, length int) ([]byte, error) {
   258  	return nil, errors.New("crypto/tls: ExportKeyingMaterial is unavailable when renegotiation is enabled")
   259  }
   260  
   261  // noEKMBecauseNoEMS is used as a value of ConnectionState.ekm when Extended
   262  // Master Secret is not negotiated and thus we wish to fail all key-material
   263  // export requests.
   264  func noEKMBecauseNoEMS(label string, context []byte, length int) ([]byte, error) {
   265  	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")
   266  }
   267  
   268  // ekmFromMasterSecret generates exported keying material as defined in RFC 5705.
   269  func ekmFromMasterSecret(version uint16, suite *cipherSuite, masterSecret, clientRandom, serverRandom []byte) func(string, []byte, int) ([]byte, error) {
   270  	return func(label string, context []byte, length int) ([]byte, error) {
   271  		switch label {
   272  		case "client finished", "server finished", "master secret", "key expansion":
   273  			// These values are reserved and may not be used.
   274  			return nil, fmt.Errorf("crypto/tls: reserved ExportKeyingMaterial label: %s", label)
   275  		}
   276  
   277  		seedLen := len(serverRandom) + len(clientRandom)
   278  		if context != nil {
   279  			seedLen += 2 + len(context)
   280  		}
   281  		seed := make([]byte, 0, seedLen)
   282  
   283  		seed = append(seed, clientRandom...)
   284  		seed = append(seed, serverRandom...)
   285  
   286  		if context != nil {
   287  			if len(context) >= 1<<16 {
   288  				return nil, fmt.Errorf("crypto/tls: ExportKeyingMaterial context too long")
   289  			}
   290  			seed = append(seed, byte(len(context)>>8), byte(len(context)))
   291  			seed = append(seed, context...)
   292  		}
   293  
   294  		return prfForVersion(version, suite)(masterSecret, label, seed, length), nil
   295  	}
   296  }
   297
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