The Tor Browser / file comparison
comparison: mobile/android/base/sync/crypto/HKDF.java
mobile/android/base/sync/crypto/HKDF.java
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| 1 /* This Source Code Form is subject to the terms of the Mozilla Public | |
| 2 * License, v. 2.0. If a copy of the MPL was not distributed with this | |
| 3 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ | |
| 4 | |
| 5 package org.mozilla.gecko.sync.crypto; | |
| 6 | |
| 7 import java.security.InvalidKeyException; | |
| 8 import java.security.Key; | |
| 9 import java.security.NoSuchAlgorithmException; | |
| 10 | |
| 11 import javax.crypto.Mac; | |
| 12 import javax.crypto.spec.SecretKeySpec; | |
| 13 | |
| 14 import org.mozilla.gecko.sync.Utils; | |
| 15 | |
| 16 /* | |
| 17 * A standards-compliant implementation of RFC 5869 | |
| 18 * for HMAC-based Key Derivation Function. | |
| 19 * HMAC uses HMAC SHA256 standard. | |
| 20 */ | |
| 21 public class HKDF { | |
| 22 public static String HMAC_ALGORITHM = "hmacSHA256"; | |
| 23 | |
| 24 /** | |
| 25 * Used for conversion in cases in which you *know* the encoding exists. | |
| 26 */ | |
| 27 public static final byte[] bytes(String in) { | |
| 28 try { | |
| 29 return in.getBytes("UTF-8"); | |
| 30 } catch (java.io.UnsupportedEncodingException e) { | |
| 31 return null; | |
| 32 } | |
| 33 } | |
| 34 | |
| 35 public static final int BLOCKSIZE = 256 / 8; | |
| 36 public static final byte[] HMAC_INPUT = bytes("Sync-AES_256_CBC-HMAC256"); | |
| 37 | |
| 38 /* | |
| 39 * Step 1 of RFC 5869 | |
| 40 * Get sha256HMAC Bytes | |
| 41 * Input: salt (message), IKM (input keyring material) | |
| 42 * Output: PRK (pseudorandom key) | |
| 43 */ | |
| 44 public static byte[] hkdfExtract(byte[] salt, byte[] IKM) throws NoSuchAlgorithmException, InvalidKeyException { | |
| 45 return digestBytes(IKM, makeHMACHasher(salt)); | |
| 46 } | |
| 47 | |
| 48 /* | |
| 49 * Step 2 of RFC 5869. | |
| 50 * Input: PRK from step 1, info, length. | |
| 51 * Output: OKM (output keyring material). | |
| 52 */ | |
| 53 public static byte[] hkdfExpand(byte[] prk, byte[] info, int len) throws NoSuchAlgorithmException, InvalidKeyException { | |
| 54 Mac hmacHasher = makeHMACHasher(prk); | |
| 55 | |
| 56 byte[] T = {}; | |
| 57 byte[] Tn = {}; | |
| 58 | |
| 59 int iterations = (int) Math.ceil(((double)len) / ((double)BLOCKSIZE)); | |
| 60 for (int i = 0; i < iterations; i++) { | |
| 61 Tn = digestBytes(Utils.concatAll(Tn, info, Utils.hex2Byte(Integer.toHexString(i + 1))), | |
| 62 hmacHasher); | |
| 63 T = Utils.concatAll(T, Tn); | |
| 64 } | |
| 65 | |
| 66 byte[] result = new byte[len]; | |
| 67 System.arraycopy(T, 0, result, 0, len); | |
| 68 return result; | |
| 69 } | |
| 70 | |
| 71 /* | |
| 72 * Make HMAC key | |
| 73 * Input: key (salt) | |
| 74 * Output: Key HMAC-Key | |
| 75 */ | |
| 76 public static Key makeHMACKey(byte[] key) { | |
| 77 if (key.length == 0) { | |
| 78 key = new byte[BLOCKSIZE]; | |
| 79 } | |
| 80 return new SecretKeySpec(key, HMAC_ALGORITHM); | |
| 81 } | |
| 82 | |
| 83 /* | |
| 84 * Make an HMAC hasher | |
| 85 * Input: Key hmacKey | |
| 86 * Ouput: An HMAC Hasher | |
| 87 */ | |
| 88 public static Mac makeHMACHasher(byte[] key) throws NoSuchAlgorithmException, InvalidKeyException { | |
| 89 Mac hmacHasher = null; | |
| 90 hmacHasher = Mac.getInstance(HMAC_ALGORITHM); | |
| 91 | |
| 92 // If Mac.getInstance doesn't throw NoSuchAlgorithmException, hmacHasher is | |
| 93 // non-null. | |
| 94 assert(hmacHasher != null); | |
| 95 | |
| 96 hmacHasher.init(makeHMACKey(key)); | |
| 97 return hmacHasher; | |
| 98 } | |
| 99 | |
| 100 /* | |
| 101 * Hash bytes with given hasher | |
| 102 * Input: message to hash, HMAC hasher | |
| 103 * Output: hashed byte[]. | |
| 104 */ | |
| 105 public static byte[] digestBytes(byte[] message, Mac hasher) { | |
| 106 hasher.update(message); | |
| 107 byte[] ret = hasher.doFinal(); | |
| 108 hasher.reset(); | |
| 109 return ret; | |
| 110 } | |
| 111 | |
| 112 public static byte[] derive(byte[] skm, byte[] xts, byte[] ctxInfo, int dkLen) throws InvalidKeyException, NoSuchAlgorithmException { | |
| 113 return hkdfExpand(hkdfExtract(xts, skm), ctxInfo, dkLen); | |
| 114 } | |
| 115 | |
| 116 public static void deriveMany(byte[] skm, byte[] xts, byte[] ctxInfo, byte[]... keys) throws InvalidKeyException, NoSuchAlgorithmException { | |
| 117 int length = 0; | |
| 118 for (byte[] key : keys) { | |
| 119 length += key.length; | |
| 120 } | |
| 121 byte[] derived = hkdfExpand(hkdfExtract(xts, skm), ctxInfo, length); | |
| 122 int offset = 0; | |
| 123 for (byte[] key : keys) { | |
| 124 System.arraycopy(derived, offset, key, 0, key.length); | |
| 125 offset += key.length; | |
| 126 } | |
| 127 } | |
| 128 } |
