1 | /**
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2 | * Hash-based Message Authentication Code implementation. Requires a message
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3 | * digest object that can be obtained, for example, from forge.md.sha1 or
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4 | * forge.md.md5.
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5 | *
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6 | * @author Dave Longley
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7 | *
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8 | * Copyright (c) 2010-2012 Digital Bazaar, Inc. All rights reserved.
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9 | */
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10 | var forge = require('./forge');
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11 | require('./md');
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12 | require('./util');
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13 |
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14 | /* HMAC API */
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15 | var hmac = module.exports = forge.hmac = forge.hmac || {};
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16 |
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17 | /**
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18 | * Creates an HMAC object that uses the given message digest object.
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19 | *
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20 | * @return an HMAC object.
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21 | */
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22 | hmac.create = function() {
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23 | // the hmac key to use
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24 | var _key = null;
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25 |
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26 | // the message digest to use
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27 | var _md = null;
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28 |
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29 | // the inner padding
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30 | var _ipadding = null;
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31 |
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32 | // the outer padding
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33 | var _opadding = null;
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34 |
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35 | // hmac context
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36 | var ctx = {};
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37 |
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38 | /**
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39 | * Starts or restarts the HMAC with the given key and message digest.
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40 | *
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41 | * @param md the message digest to use, null to reuse the previous one,
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42 | * a string to use builtin 'sha1', 'md5', 'sha256'.
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43 | * @param key the key to use as a string, array of bytes, byte buffer,
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44 | * or null to reuse the previous key.
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45 | */
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46 | ctx.start = function(md, key) {
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47 | if(md !== null) {
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48 | if(typeof md === 'string') {
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49 | // create builtin message digest
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50 | md = md.toLowerCase();
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51 | if(md in forge.md.algorithms) {
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52 | _md = forge.md.algorithms[md].create();
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53 | } else {
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54 | throw new Error('Unknown hash algorithm "' + md + '"');
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55 | }
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56 | } else {
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57 | // store message digest
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58 | _md = md;
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59 | }
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60 | }
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61 |
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62 | if(key === null) {
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63 | // reuse previous key
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64 | key = _key;
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65 | } else {
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66 | if(typeof key === 'string') {
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67 | // convert string into byte buffer
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68 | key = forge.util.createBuffer(key);
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69 | } else if(forge.util.isArray(key)) {
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70 | // convert byte array into byte buffer
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71 | var tmp = key;
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72 | key = forge.util.createBuffer();
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73 | for(var i = 0; i < tmp.length; ++i) {
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74 | key.putByte(tmp[i]);
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75 | }
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76 | }
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77 |
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78 | // if key is longer than blocksize, hash it
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79 | var keylen = key.length();
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80 | if(keylen > _md.blockLength) {
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81 | _md.start();
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82 | _md.update(key.bytes());
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83 | key = _md.digest();
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84 | }
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85 |
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86 | // mix key into inner and outer padding
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87 | // ipadding = [0x36 * blocksize] ^ key
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88 | // opadding = [0x5C * blocksize] ^ key
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89 | _ipadding = forge.util.createBuffer();
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90 | _opadding = forge.util.createBuffer();
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91 | keylen = key.length();
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92 | for(var i = 0; i < keylen; ++i) {
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93 | var tmp = key.at(i);
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94 | _ipadding.putByte(0x36 ^ tmp);
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95 | _opadding.putByte(0x5C ^ tmp);
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96 | }
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97 |
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98 | // if key is shorter than blocksize, add additional padding
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99 | if(keylen < _md.blockLength) {
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100 | var tmp = _md.blockLength - keylen;
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101 | for(var i = 0; i < tmp; ++i) {
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102 | _ipadding.putByte(0x36);
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103 | _opadding.putByte(0x5C);
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104 | }
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105 | }
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106 | _key = key;
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107 | _ipadding = _ipadding.bytes();
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108 | _opadding = _opadding.bytes();
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109 | }
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110 |
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111 | // digest is done like so: hash(opadding | hash(ipadding | message))
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112 |
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113 | // prepare to do inner hash
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114 | // hash(ipadding | message)
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115 | _md.start();
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116 | _md.update(_ipadding);
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117 | };
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118 |
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119 | /**
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120 | * Updates the HMAC with the given message bytes.
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121 | *
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122 | * @param bytes the bytes to update with.
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123 | */
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124 | ctx.update = function(bytes) {
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125 | _md.update(bytes);
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126 | };
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127 |
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128 | /**
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129 | * Produces the Message Authentication Code (MAC).
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130 | *
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131 | * @return a byte buffer containing the digest value.
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132 | */
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133 | ctx.getMac = function() {
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134 | // digest is done like so: hash(opadding | hash(ipadding | message))
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135 | // here we do the outer hashing
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136 | var inner = _md.digest().bytes();
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137 | _md.start();
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138 | _md.update(_opadding);
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139 | _md.update(inner);
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140 | return _md.digest();
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141 | };
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142 | // alias for getMac
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143 | ctx.digest = ctx.getMac;
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144 |
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145 | return ctx;
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146 | };
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