libgo/go/crypto/tls/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 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 }