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-Go file.
4
5package xtls
6
7import (
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.
20func 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.
27func 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.
48func 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.
67func 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
77const (
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
82var masterSecretLabel = []byte("master secret")
83var keyExpansionLabel = []byte("key expansion")
84var clientFinishedLabel = []byte("client finished")
85var serverFinishedLabel = []byte("server finished")
86
87func 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
101func 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.
108func 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.
121func 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
143func 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.
159type 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
174func (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
190func (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.
202func (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.
210func (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.
218func (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.
242func (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.
249func 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.
254func 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