Source file src/pkg/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/hmac"
     9		"crypto/md5"
    10		"crypto/sha1"
    11		"hash"
    12	)
    13	
    14	// Split a premaster secret in two as specified in RFC 4346, section 5.
    15	func splitPreMasterSecret(secret []byte) (s1, s2 []byte) {
    16		s1 = secret[0 : (len(secret)+1)/2]
    17		s2 = secret[len(secret)/2:]
    18		return
    19	}
    20	
    21	// pHash implements the P_hash function, as defined in RFC 4346, section 5.
    22	func pHash(result, secret, seed []byte, hash func() hash.Hash) {
    23		h := hmac.New(hash, secret)
    24		h.Write(seed)
    25		a := h.Sum(nil)
    26	
    27		j := 0
    28		for j < len(result) {
    29			h.Reset()
    30			h.Write(a)
    31			h.Write(seed)
    32			b := h.Sum(nil)
    33			todo := len(b)
    34			if j+todo > len(result) {
    35				todo = len(result) - j
    36			}
    37			copy(result[j:j+todo], b)
    38			j += todo
    39	
    40			h.Reset()
    41			h.Write(a)
    42			a = h.Sum(nil)
    43		}
    44	}
    45	
    46	// pRF10 implements the TLS 1.0 pseudo-random function, as defined in RFC 2246, section 5.
    47	func pRF10(result, secret, label, seed []byte) {
    48		hashSHA1 := sha1.New
    49		hashMD5 := md5.New
    50	
    51		labelAndSeed := make([]byte, len(label)+len(seed))
    52		copy(labelAndSeed, label)
    53		copy(labelAndSeed[len(label):], seed)
    54	
    55		s1, s2 := splitPreMasterSecret(secret)
    56		pHash(result, s1, labelAndSeed, hashMD5)
    57		result2 := make([]byte, len(result))
    58		pHash(result2, s2, labelAndSeed, hashSHA1)
    59	
    60		for i, b := range result2 {
    61			result[i] ^= b
    62		}
    63	}
    64	
    65	// pRF30 implements the SSL 3.0 pseudo-random function, as defined in
    66	// www.mozilla.org/projects/security/pki/nss/ssl/draft302.txt section 6.
    67	func pRF30(result, secret, label, seed []byte) {
    68		hashSHA1 := sha1.New()
    69		hashMD5 := md5.New()
    70	
    71		done := 0
    72		i := 0
    73		// RFC5246 section 6.3 says that the largest PRF output needed is 128
    74		// bytes. Since no more ciphersuites will be added to SSLv3, this will
    75		// remain true. Each iteration gives us 16 bytes so 10 iterations will
    76		// be sufficient.
    77		var b [11]byte
    78		for done < len(result) {
    79			for j := 0; j <= i; j++ {
    80				b[j] = 'A' + byte(i)
    81			}
    82	
    83			hashSHA1.Reset()
    84			hashSHA1.Write(b[:i+1])
    85			hashSHA1.Write(secret)
    86			hashSHA1.Write(seed)
    87			digest := hashSHA1.Sum(nil)
    88	
    89			hashMD5.Reset()
    90			hashMD5.Write(secret)
    91			hashMD5.Write(digest)
    92	
    93			done += copy(result[done:], hashMD5.Sum(nil))
    94			i++
    95		}
    96	}
    97	
    98	const (
    99		tlsRandomLength      = 32 // Length of a random nonce in TLS 1.1.
   100		masterSecretLength   = 48 // Length of a master secret in TLS 1.1.
   101		finishedVerifyLength = 12 // Length of verify_data in a Finished message.
   102	)
   103	
   104	var masterSecretLabel = []byte("master secret")
   105	var keyExpansionLabel = []byte("key expansion")
   106	var clientFinishedLabel = []byte("client finished")
   107	var serverFinishedLabel = []byte("server finished")
   108	
   109	// keysFromPreMasterSecret generates the connection keys from the pre master
   110	// secret, given the lengths of the MAC key, cipher key and IV, as defined in
   111	// RFC 2246, section 6.3.
   112	func keysFromPreMasterSecret(version uint16, preMasterSecret, clientRandom, serverRandom []byte, macLen, keyLen, ivLen int) (masterSecret, clientMAC, serverMAC, clientKey, serverKey, clientIV, serverIV []byte) {
   113		prf := pRF10
   114		if version == versionSSL30 {
   115			prf = pRF30
   116		}
   117	
   118		var seed [tlsRandomLength * 2]byte
   119		copy(seed[0:len(clientRandom)], clientRandom)
   120		copy(seed[len(clientRandom):], serverRandom)
   121		masterSecret = make([]byte, masterSecretLength)
   122		prf(masterSecret, preMasterSecret, masterSecretLabel, seed[0:])
   123	
   124		copy(seed[0:len(clientRandom)], serverRandom)
   125		copy(seed[len(serverRandom):], clientRandom)
   126	
   127		n := 2*macLen + 2*keyLen + 2*ivLen
   128		keyMaterial := make([]byte, n)
   129		prf(keyMaterial, masterSecret, keyExpansionLabel, seed[0:])
   130		clientMAC = keyMaterial[:macLen]
   131		keyMaterial = keyMaterial[macLen:]
   132		serverMAC = keyMaterial[:macLen]
   133		keyMaterial = keyMaterial[macLen:]
   134		clientKey = keyMaterial[:keyLen]
   135		keyMaterial = keyMaterial[keyLen:]
   136		serverKey = keyMaterial[:keyLen]
   137		keyMaterial = keyMaterial[keyLen:]
   138		clientIV = keyMaterial[:ivLen]
   139		keyMaterial = keyMaterial[ivLen:]
   140		serverIV = keyMaterial[:ivLen]
   141		return
   142	}
   143	
   144	func newFinishedHash(version uint16) finishedHash {
   145		return finishedHash{md5.New(), sha1.New(), md5.New(), sha1.New(), version}
   146	}
   147	
   148	// A finishedHash calculates the hash of a set of handshake messages suitable
   149	// for including in a Finished message.
   150	type finishedHash struct {
   151		clientMD5  hash.Hash
   152		clientSHA1 hash.Hash
   153		serverMD5  hash.Hash
   154		serverSHA1 hash.Hash
   155		version    uint16
   156	}
   157	
   158	func (h finishedHash) Write(msg []byte) (n int, err error) {
   159		h.clientMD5.Write(msg)
   160		h.clientSHA1.Write(msg)
   161		h.serverMD5.Write(msg)
   162		h.serverSHA1.Write(msg)
   163		return len(msg), nil
   164	}
   165	
   166	// finishedSum10 calculates the contents of the verify_data member of a TLSv1
   167	// Finished message given the MD5 and SHA1 hashes of a set of handshake
   168	// messages.
   169	func finishedSum10(md5, sha1, label, masterSecret []byte) []byte {
   170		seed := make([]byte, len(md5)+len(sha1))
   171		copy(seed, md5)
   172		copy(seed[len(md5):], sha1)
   173		out := make([]byte, finishedVerifyLength)
   174		pRF10(out, masterSecret, label, seed)
   175		return out
   176	}
   177	
   178	// finishedSum30 calculates the contents of the verify_data member of a SSLv3
   179	// Finished message given the MD5 and SHA1 hashes of a set of handshake
   180	// messages.
   181	func finishedSum30(md5, sha1 hash.Hash, masterSecret []byte, magic [4]byte) []byte {
   182		md5.Write(magic[:])
   183		md5.Write(masterSecret)
   184		md5.Write(ssl30Pad1[:])
   185		md5Digest := md5.Sum(nil)
   186	
   187		md5.Reset()
   188		md5.Write(masterSecret)
   189		md5.Write(ssl30Pad2[:])
   190		md5.Write(md5Digest)
   191		md5Digest = md5.Sum(nil)
   192	
   193		sha1.Write(magic[:])
   194		sha1.Write(masterSecret)
   195		sha1.Write(ssl30Pad1[:40])
   196		sha1Digest := sha1.Sum(nil)
   197	
   198		sha1.Reset()
   199		sha1.Write(masterSecret)
   200		sha1.Write(ssl30Pad2[:40])
   201		sha1.Write(sha1Digest)
   202		sha1Digest = sha1.Sum(nil)
   203	
   204		ret := make([]byte, len(md5Digest)+len(sha1Digest))
   205		copy(ret, md5Digest)
   206		copy(ret[len(md5Digest):], sha1Digest)
   207		return ret
   208	}
   209	
   210	var ssl3ClientFinishedMagic = [4]byte{0x43, 0x4c, 0x4e, 0x54}
   211	var ssl3ServerFinishedMagic = [4]byte{0x53, 0x52, 0x56, 0x52}
   212	
   213	// clientSum returns the contents of the verify_data member of a client's
   214	// Finished message.
   215	func (h finishedHash) clientSum(masterSecret []byte) []byte {
   216		if h.version == versionSSL30 {
   217			return finishedSum30(h.clientMD5, h.clientSHA1, masterSecret, ssl3ClientFinishedMagic)
   218		}
   219	
   220		md5 := h.clientMD5.Sum(nil)
   221		sha1 := h.clientSHA1.Sum(nil)
   222		return finishedSum10(md5, sha1, clientFinishedLabel, masterSecret)
   223	}
   224	
   225	// serverSum returns the contents of the verify_data member of a server's
   226	// Finished message.
   227	func (h finishedHash) serverSum(masterSecret []byte) []byte {
   228		if h.version == versionSSL30 {
   229			return finishedSum30(h.serverMD5, h.serverSHA1, masterSecret, ssl3ServerFinishedMagic)
   230		}
   231	
   232		md5 := h.serverMD5.Sum(nil)
   233		sha1 := h.serverSHA1.Sum(nil)
   234		return finishedSum10(md5, sha1, serverFinishedLabel, masterSecret)
   235	}