1 /*
2 * Copyright 2019 The Netty Project
3 *
4 * The Netty Project licenses this file to you under the Apache License,
5 * version 2.0 (the "License"); you may not use this file except in compliance
6 * with the License. You may obtain a copy of the License at:
7 *
8 * https://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
12 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
13 * License for the specific language governing permissions and limitations
14 * under the License.
15 */
16 package io.netty.handler.ssl;
17
18 import static io.netty.util.internal.ObjectUtil.checkPositiveOrZero;
19
20 import io.netty.util.internal.EmptyArrays;
21
22 import javax.crypto.Mac;
23 import javax.crypto.spec.SecretKeySpec;
24 import java.security.GeneralSecurityException;
25 import java.util.Arrays;
26
27 /**
28 * This pseudorandom function (PRF) takes as input a secret, a seed, and
29 * an identifying label and produces an output of arbitrary length.
30 *
31 * This is used by the TLS RFC to construct/deconstruct an array of bytes into
32 * composite secrets.
33 *
34 * {@link <a href="https://tools.ietf.org/html/rfc5246">rfc5246</a>}
35 */
36 final class PseudoRandomFunction {
37
38 /**
39 * Constructor never to be called.
40 */
41 private PseudoRandomFunction() {
42 }
43
44 /**
45 * Use a single hash function to expand a secret and seed into an
46 * arbitrary quantity of output.
47 *
48 * P_hash(secret, seed) = HMAC_hash(secret, A(1) + seed) +
49 * HMAC_hash(secret, A(2) + seed) +
50 * HMAC_hash(secret, A(3) + seed) + ...
51 * where + indicates concatenation.
52 * A() is defined as:
53 * A(0) = seed
54 * A(i) = HMAC_hash(secret, A(i-1))
55 * @param secret The starting secret to use for expansion
56 * @param label An ascii string without a length byte or trailing null character.
57 * @param seed The seed of the hash
58 * @param length The number of bytes to return
59 * @param algo the hmac algorithm to use
60 * @return The expanded secrets
61 * @throws IllegalArgumentException if the algo could not be found.
62 */
63 static byte[] hash(byte[] secret, byte[] label, byte[] seed, int length, String algo) {
64 checkPositiveOrZero(length, "length");
65 try {
66 Mac hmac = Mac.getInstance(algo);
67 hmac.init(new SecretKeySpec(secret, algo));
68 /*
69 * P_hash(secret, seed) = HMAC_hash(secret, A(1) + seed) +
70 * HMAC_hash(secret, A(2) + seed) + HMAC_hash(secret, A(3) + seed) + ...
71 * where + indicates concatenation. A() is defined as: A(0) = seed, A(i)
72 * = HMAC_hash(secret, A(i-1))
73 */
74
75 int iterations = (int) Math.ceil(length / (double) hmac.getMacLength());
76 byte[] expansion = EmptyArrays.EMPTY_BYTES;
77 byte[] data = concat(label, seed);
78 byte[] A = data;
79 for (int i = 0; i < iterations; i++) {
80 A = hmac.doFinal(A);
81 expansion = concat(expansion, hmac.doFinal(concat(A, data)));
82 }
83 return Arrays.copyOf(expansion, length);
84 } catch (GeneralSecurityException e) {
85 throw new IllegalArgumentException("Could not find algo: " + algo, e);
86 }
87 }
88
89 private static byte[] concat(byte[] first, byte[] second) {
90 byte[] result = Arrays.copyOf(first, first.length + second.length);
91 System.arraycopy(second, 0, result, first.length, second.length);
92 return result;
93 }
94 }
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