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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	// masterFromPreMasterSecret generates the master secret from the pre-master
   110	// secret. See http://tools.ietf.org/html/rfc5246#section-8.1
   111	func masterFromPreMasterSecret(version uint16, preMasterSecret, clientRandom, serverRandom []byte) []byte {
   112		prf := pRF10
   113		if version == versionSSL30 {
   114			prf = pRF30
   115		}
   116	
   117		var seed [tlsRandomLength * 2]byte
   118		copy(seed[0:len(clientRandom)], clientRandom)
   119		copy(seed[len(clientRandom):], serverRandom)
   120		masterSecret := make([]byte, masterSecretLength)
   121		prf(masterSecret, preMasterSecret, masterSecretLabel, seed[0:])
   122		return masterSecret
   123	}
   124	
   125	// keysFromMasterSecret generates the connection keys from the master
   126	// secret, given the lengths of the MAC key, cipher key and IV, as defined in
   127	// RFC 2246, section 6.3.
   128	func keysFromMasterSecret(version uint16, masterSecret, clientRandom, serverRandom []byte, macLen, keyLen, ivLen int) (clientMAC, serverMAC, clientKey, serverKey, clientIV, serverIV []byte) {
   129		prf := pRF10
   130		if version == versionSSL30 {
   131			prf = pRF30
   132		}
   133	
   134		var seed [tlsRandomLength * 2]byte
   135		copy(seed[0:len(clientRandom)], serverRandom)
   136		copy(seed[len(serverRandom):], clientRandom)
   137	
   138		n := 2*macLen + 2*keyLen + 2*ivLen
   139		keyMaterial := make([]byte, n)
   140		prf(keyMaterial, masterSecret, keyExpansionLabel, seed[0:])
   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) finishedHash {
   156		return finishedHash{md5.New(), sha1.New(), md5.New(), sha1.New(), version}
   157	}
   158	
   159	// A finishedHash calculates the hash of a set of handshake messages suitable
   160	// for including in a Finished message.
   161	type finishedHash struct {
   162		clientMD5  hash.Hash
   163		clientSHA1 hash.Hash
   164		serverMD5  hash.Hash
   165		serverSHA1 hash.Hash
   166		version    uint16
   167	}
   168	
   169	func (h finishedHash) Write(msg []byte) (n int, err error) {
   170		h.clientMD5.Write(msg)
   171		h.clientSHA1.Write(msg)
   172		h.serverMD5.Write(msg)
   173		h.serverSHA1.Write(msg)
   174		return len(msg), nil
   175	}
   176	
   177	// finishedSum10 calculates the contents of the verify_data member of a TLSv1
   178	// Finished message given the MD5 and SHA1 hashes of a set of handshake
   179	// messages.
   180	func finishedSum10(md5, sha1, label, masterSecret []byte) []byte {
   181		seed := make([]byte, len(md5)+len(sha1))
   182		copy(seed, md5)
   183		copy(seed[len(md5):], sha1)
   184		out := make([]byte, finishedVerifyLength)
   185		pRF10(out, masterSecret, label, seed)
   186		return out
   187	}
   188	
   189	// finishedSum30 calculates the contents of the verify_data member of a SSLv3
   190	// Finished message given the MD5 and SHA1 hashes of a set of handshake
   191	// messages.
   192	func finishedSum30(md5, sha1 hash.Hash, masterSecret []byte, magic [4]byte) []byte {
   193		md5.Write(magic[:])
   194		md5.Write(masterSecret)
   195		md5.Write(ssl30Pad1[:])
   196		md5Digest := md5.Sum(nil)
   197	
   198		md5.Reset()
   199		md5.Write(masterSecret)
   200		md5.Write(ssl30Pad2[:])
   201		md5.Write(md5Digest)
   202		md5Digest = md5.Sum(nil)
   203	
   204		sha1.Write(magic[:])
   205		sha1.Write(masterSecret)
   206		sha1.Write(ssl30Pad1[:40])
   207		sha1Digest := sha1.Sum(nil)
   208	
   209		sha1.Reset()
   210		sha1.Write(masterSecret)
   211		sha1.Write(ssl30Pad2[:40])
   212		sha1.Write(sha1Digest)
   213		sha1Digest = sha1.Sum(nil)
   214	
   215		ret := make([]byte, len(md5Digest)+len(sha1Digest))
   216		copy(ret, md5Digest)
   217		copy(ret[len(md5Digest):], sha1Digest)
   218		return ret
   219	}
   220	
   221	var ssl3ClientFinishedMagic = [4]byte{0x43, 0x4c, 0x4e, 0x54}
   222	var ssl3ServerFinishedMagic = [4]byte{0x53, 0x52, 0x56, 0x52}
   223	
   224	// clientSum returns the contents of the verify_data member of a client's
   225	// Finished message.
   226	func (h finishedHash) clientSum(masterSecret []byte) []byte {
   227		if h.version == versionSSL30 {
   228			return finishedSum30(h.clientMD5, h.clientSHA1, masterSecret, ssl3ClientFinishedMagic)
   229		}
   230	
   231		md5 := h.clientMD5.Sum(nil)
   232		sha1 := h.clientSHA1.Sum(nil)
   233		return finishedSum10(md5, sha1, clientFinishedLabel, masterSecret)
   234	}
   235	
   236	// serverSum returns the contents of the verify_data member of a server's
   237	// Finished message.
   238	func (h finishedHash) serverSum(masterSecret []byte) []byte {
   239		if h.version == versionSSL30 {
   240			return finishedSum30(h.serverMD5, h.serverSHA1, masterSecret, ssl3ServerFinishedMagic)
   241		}
   242	
   243		md5 := h.serverMD5.Sum(nil)
   244		sha1 := h.serverSHA1.Sum(nil)
   245		return finishedSum10(md5, sha1, serverFinishedLabel, masterSecret)
   246	}

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