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1 | NAME |
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2 | Crypt::Spritz - Spritz stream cipher/hash/MAC/AEAD/CSPRNG module |
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3 | |
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4 | SYNOPSIS |
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5 | use Crypt::Spritz; |
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6 | |
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7 | # see the commented examples in their respective classes, |
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8 | # but basically |
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9 | |
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10 | my $cipher = new Crypt::Spritz::Cipher::XOR $key, $iv; |
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11 | $ciphertext = $cipher->crypt ($cleartext); |
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12 | |
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13 | my $hasher = new Crypt::Spritz::Hash; |
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14 | $hasher->add ($data); |
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15 | $digest = $hasher->finish; |
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16 | |
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17 | my $hasher = new Crypt::Spritz::MAC $key; |
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18 | $hasher->add ($data); |
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19 | $mac = $hasher->finish; |
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20 | |
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21 | my $aead = new Crypt::Spritz::AEAD::XOR $key; |
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22 | $aead->nonce ($counter); |
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23 | $aead->associated_data ($header); |
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24 | $ciphertext = $aead->crypt ($cleartext); |
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25 | $mac = $aead->mac; |
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26 | |
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27 | my $prng = new Crypt::Spritz::PRNG $entropy; |
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28 | $prng->add ($additional_entropy); |
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29 | $keydata = $prng->get (32); |
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30 | |
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31 | DESCRIPTION |
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32 | This module implements the Spritz spongelike function (with N=256), the |
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33 | spiritual successor of RC4 developed by Ron Rivest and Jacob Schuldt. |
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34 | |
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35 | Its strength is extreme versatility (you get a stream cipher, a hash, a |
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36 | MAC, a DRBG/CSPRNG, an authenticated encryption block/stream cipher and |
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37 | more) and extremely simple and small code (encryption and authentication |
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38 | can be had in 1KB of compiled code on amd64, which isn't an issue for |
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39 | most uses in Perl, but is useful in embedded situations, or e.g. when |
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40 | doing crypto using javascript in a browser and communicating with Perl). |
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41 | |
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42 | Its weakness is its relatively slow speed (encryption is a few times |
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43 | slower than RC4 or AES, hashing many times slower than SHA-3, although |
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44 | this might be reversed on an 8-bit-cpu) and the fact that it is totally |
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45 | unproven in the field (as of this writing, the cipher was just a few |
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46 | months old), so it can't be called production-ready. |
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47 | |
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48 | All the usual caveats regarding stream ciphers apply - never repeat your |
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49 | key, never repeat your nonce and so on - you should have some basic |
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50 | understanding of cryptography before using this cipher in your own |
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51 | designs. |
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52 | |
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53 | The Spritz base class is not meant for end users. To make usage simpler |
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54 | and safer, a number of convenience classes are provided for typical |
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55 | end-user tasks: |
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56 | |
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57 | encryption - Crypt::Spritz::Cipher::XOR |
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58 | hashing - Crypt::Spritz::Hash |
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59 | message authentication - Crypt::Spritz::MAC |
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60 | authenticated encryption - Crypt::Spritz::AEAD::XOR |
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61 | random number generation - Crypt::Spritz::PRNG |
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62 | |
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63 | THE Crypt::Spritz CLASS |
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64 | This class implements most of the Spritz primitives. To use it |
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65 | effectively you should understand them, for example, by reading the |
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66 | "http://people.csail.mit.edu/rivest/pubs/RS14.pdf" in Spritz paper, |
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67 | especially pp. 5-6. |
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68 | |
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69 | The Spritz primitive corresponding to the Perl method is given as |
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70 | comment. |
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71 | |
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72 | $spritz = new Crypt::Spritz # InitializeState |
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73 | Creates and returns a new, initialised Spritz state. |
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74 | |
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75 | $spritz->init # InitializeState |
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76 | Initialises the Spritz state again, throwing away the previous |
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77 | state. |
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78 | |
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79 | $spritz->update # Update |
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80 | $spritz->whip ($r) # Whip |
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81 | $spritz->crush # Crush |
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82 | $spritz->shuffle # Shuffle |
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83 | $spritz->output # Output |
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84 | Calls the Spritz primitive ovf the same name - these are not |
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85 | normally called manually. |
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86 | |
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87 | $spritz->absorb ($I) # Absorb |
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88 | Absorbs the given data into the state (usually used for key |
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89 | material, nonces, IVs messages to be hashed and so on). |
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90 | |
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91 | $spritz->absorb_stop # AbsorbStop |
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92 | Absorbs a special stop symbol - this is usually used as delimiter |
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93 | between multiple strings to be absorbed, to thwart extension |
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94 | attacks. |
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95 | |
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96 | $spritz->absorb_and_stop ($I) |
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97 | This is a convenience function that simply calls "absorb" followed |
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98 | by "absorb_stop". |
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99 | |
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100 | $octet = $spritz->drip # Drip |
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101 | Squeezes out a single byte from the state. |
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102 | |
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103 | $octets = $spritz->squeeze ($len) # Squeeze |
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104 | Squeezes out the requested number of bytes from the state - this is |
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105 | usually |
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106 | |
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107 | THE Crypt::Spritz::Cipher::XOR CLASS |
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108 | This class implements stream encryption/decryption. It doesn't implement |
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109 | the standard Spritz encryption but the XOR variant (called spritz-xor in |
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110 | the paper). |
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111 | |
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112 | The XOR variant should be as secure as the standard variant, but doesn't |
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113 | have separate encryption and decryaption functions, which saves |
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114 | codesize. IT is not compatible with standard Spritz encryption, however |
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115 | - drop me a note if you want that implemented as well. |
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116 | |
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117 | Typical use for encryption *and* decryption (code is identical for |
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118 | decryption, you simply pass the encrypted data to "crypt"): |
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119 | |
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120 | # create a cipher - $salt can be a random string you send |
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121 | # with your message, in clear, a counter (best), or empty if |
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122 | # you only want to encrypt one message with the given key. |
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123 | # 16 or 32 octets are typical sizes for the key, for the salt, |
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124 | # use whatever you need to give a unique salt for every |
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125 | # message you encrypt with the same key. |
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126 | |
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127 | my $cipher = Crypt::Spritz::Cipher::XOR $key, $salt; |
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128 | |
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129 | # encrypt a message in one or more calls to crypt |
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130 | |
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131 | my $encrypted; |
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132 | |
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133 | $encrypted .= $cipher->crypt ("This is"); |
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134 | $encrypted .= $cipher->crypt ("all very"); |
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135 | $encrypted .= $cipher->crypt ("secret"); |
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136 | |
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137 | # that's all |
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138 | |
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139 | $cipher = new Crypt::Spritz::Cipher::XOR $key[, $iv] |
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140 | Creates a new cipher object usable for encryption and decryption. |
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141 | The $key must be provided, the initial vector $IV is optional. |
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142 | |
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143 | Both $key and $IV can be of any length. Typical lengths for the $key |
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144 | are 16 (128 bit) or 32 (256 bit), while the $IV simply needs to be |
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145 | long enough to distinguish repeated uses of tghe same key. |
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146 | |
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147 | $encrypted = $cipher->crypt ($cleartext) |
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148 | $cleartext = $cipher->crypt ($encrypted) |
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149 | Encrypt or decrypt a piece of a message. This cna be called as many |
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150 | times as you want, and the message can be split into as few or many |
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151 | pieces as required without affecting the results. |
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152 | |
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153 | $cipher->crypt_inplace ($cleartext_or_ciphertext) |
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154 | Same as "crypt", except it *modifies the argument in-place*. |
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155 | |
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156 | $constant_32 = $cipher->keysize |
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157 | $constant_64 = $cipher->blocksize |
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158 | These methods are provided for Crypt::CBC compatibility and simply |
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159 | return 32 and 64, respectively. |
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160 | |
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161 | Note that it is pointless to use Spritz with Crypt::CBC, as Spritz |
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162 | is not a block cipher and already provides an appropriate mode. |
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163 | |
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164 | THE Crypt::Spritz::Hash CLASS |
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165 | This implements the Spritz digest/hash algorithm. It works very similar |
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166 | to other digest modules on CPAN, such as Digest::SHA3. |
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167 | |
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168 | Typical use for hashing: |
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169 | |
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170 | # create hasher object |
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171 | my $hasher = new Crypt::Spritz::Hash; |
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172 | |
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173 | # now feed data to be hashed into $hasher |
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174 | # in as few or many calls as required |
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175 | $hasher->add ("Some data"); |
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176 | $hasher->add ("Some more"); |
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177 | |
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178 | # extract the hash - the object is not usable afterwards |
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179 | my $digest = $hasher->finish (32); |
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180 | |
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181 | $hasher = new Crypt::Spritz::Hash |
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182 | Creates a new hasher object. |
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183 | |
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184 | $hasher->add ($data) |
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185 | Adds data to be hashed into the hasher state. It doesn't matter |
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186 | whether you pass your data in in one go or split it up, the hash |
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187 | will be the same. |
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188 | |
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189 | $digest = $hasher->finish ($length) |
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190 | Calculates a hash digest of the given length and return it. The |
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191 | object cannot sensibly be used for further hashing afterwards. |
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192 | |
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193 | Typical digest lengths are 16 and 32, corresponding to 128 and 256 |
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194 | bit digests, respectively. |
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195 | |
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196 | THE Crypt::Spritz::MAC CLASS |
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197 | This implements the Spritz Message Authentication Code algorithm. It |
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198 | works very similar to other digest modules on CPAN, such as |
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199 | Digest::SHA3, but implements an authenticated digest (like |
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200 | Digest::HMAC). |
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201 | |
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202 | *Authenticated* means that, unlike Crypt::Spritz::Hash, where everybody |
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203 | can verify and recreate the hash value for some data, with a MAC, |
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204 | knowledge of the (hopefully) secret key is required both to create and |
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205 | to verify the digest. |
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206 | |
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207 | Typical use for hashing is almost the same as with Crypt::Spritz::MAC, |
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208 | except a key (typically 16 or 32 octets) is provided to the constructor: |
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209 | |
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210 | # create hasher object |
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211 | my $hasher = new Crypt::Spritz::Mac $key; |
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212 | |
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213 | # now feed data to be hashed into $hasher |
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214 | # in as few or many calls as required |
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215 | $hasher->add ("Some data"); |
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216 | $hasher->add ("Some more"); |
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217 | |
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218 | # extract the mac - the object is not usable afterwards |
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219 | my $mac = $hasher->finish (32); |
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220 | |
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221 | $hasher = new Crypt::Spritz::MAC $key |
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222 | Creates a new hasher object. The $key can be of any length, but 16 |
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223 | and 32 (128 and 256 bit) are customary. |
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224 | |
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225 | $hasher->add ($data) |
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226 | Adds data to be hashed into the hasher state. It doesn't matter |
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227 | whether you pass your data in in one go or split it up, the hash |
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228 | will be the same. |
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229 | |
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230 | $mac = $hasher->finish ($length) |
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231 | Calculates a message code of the given length and return it. The |
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232 | object cannot sensibly be used for further hashing afterwards. |
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233 | |
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234 | Typical digest lengths are 16 and 32, corresponding to 128 and 256 |
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235 | bit digests, respectively. |
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236 | |
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237 | THE Crypt::Spritz::AEAD::XOR CLASS |
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238 | This is the most complicated class - it combines encryption and message |
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239 | authentication into a single "authenticated encryption mode". It is |
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240 | similar to using both Crypt::Spritz::Cipher::XOR and Crypt::Spritz::MAC, |
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241 | but makes it harder to make mistakes in combining them. |
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242 | |
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243 | You can additionally provide cleartext data that will not be encrypted |
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244 | or decrypted, but that is nevertheless authenticated using the MAC, |
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245 | which is why this mode is called *AEAD*, *Authenticated Encryption with |
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246 | Associated Data*. Associated data is usually used to any header data |
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247 | that is in cleartext, but should nevertheless be authenticated. |
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248 | |
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249 | This implementation implements the XOR variant. Just as with |
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250 | Crypt::Spritz::Cipher::XOR, this means it is not compatible with the |
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251 | standard mode, but uses less code and doesn't distinguish between |
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252 | encryption and decryption. |
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253 | |
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254 | Typical usage is as follows: |
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255 | |
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256 | # create a new aead object |
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257 | # you use one object per message |
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258 | # key length customarily is 16 or 32 |
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259 | my $aead = new Crypt::Spritz::AEAD::XOR $key; |
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260 | |
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261 | # now you must feed the nonce. if you do not need a nonce, |
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262 | # you can provide the empty string, but you have to call it |
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263 | # after creating the object, before calling associated_data. |
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264 | # the nonce must be different for each usage of the $key. |
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265 | # a counter of some kind is good enough. |
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266 | # reusing a nonce with the same key completely |
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267 | # destroys security! |
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268 | $aead->nonce ($counter); |
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269 | |
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270 | # then you must feed any associated data you have. if you |
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271 | # do not have associated cleartext data, you can provide the empty |
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272 | # string, but you have to call it after nonce and before crypt. |
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273 | $aead->associated_data ($header); |
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274 | |
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275 | # next, you call crypt one or more times with your data |
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276 | # to be encrypted (opr decrypted). |
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277 | # all except the last call must use a length that is a |
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278 | # multiple of 64. |
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279 | # the last block can have any length. |
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280 | my $encrypted; |
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281 | |
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282 | $encrypted .= $aead->crypt ("1" x 64); |
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283 | $encrypted .= $aead->crypt ("2" x 64); |
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284 | $encrypted .= $aead->crypt ("3456"); |
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285 | |
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286 | # finally you can calculate the MAC for all of the above |
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287 | my $mac = $aead->finish; |
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288 | |
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289 | $aead = new Crypt::Spritz::AEAD::XOR $key |
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290 | Creates a new cipher object usable for encryption and decryption. |
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291 | |
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292 | The $key can be of any length. Typical lengths for the $key are 16 |
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293 | (128 bit) or 32 (256 bit). |
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294 | |
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295 | After creation, you have to call "nonce" next. |
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296 | |
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297 | $aead->nonce ($nonce) |
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298 | Provide the nonce value (nonce means "value used once"), a value the |
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299 | is unique between all uses with the same key. This method *must* be |
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300 | called *after* "new" and *before* "associated_data". |
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301 | |
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302 | If you only ever use a given key once, you can provide an empty |
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303 | nonce - but you still have to call the method. |
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304 | |
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305 | Common strategies to provide a nonce are to implement a persistent |
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306 | counter or to generate a random string of sufficient length to |
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307 | guarantee that it differs each time. |
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308 | |
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309 | The problem with counters is that you might get confused and forget |
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310 | increments, and thus reuse the same sequence number. The problem |
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311 | with random strings i that your random number generator might be |
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312 | hosed and generate the same randomness multiple times (randomness |
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313 | can be very hard to get especially on embedded devices). |
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314 | |
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315 | $aead->associated_data ($data)( |
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316 | Provide the associated data (cleartext data to be authenticated but |
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317 | not encrypted). This method *must* be called *after* "nonce" and |
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318 | *before* "crypt". |
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319 | |
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320 | If you don't have any associated data, you can provide an empty |
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321 | string - but you still have to call the method. |
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322 | |
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323 | Associated data is typically header data - data anybody is allowed |
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324 | to see in cleartext, but that should nevertheless be protected with |
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325 | an authentication code. Typically such data is used to identify |
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326 | where to forward a message to, how to find the key to decrypt the |
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327 | message or in general how to interpret the encrypted part of a |
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328 | message. |
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329 | |
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330 | $encrypted = $cipher->crypt ($cleartext) |
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331 | $cleartext = $cipher->crypt ($encrypted) |
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332 | Encrypt or decrypt a piece of a message. This cna be called as many |
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333 | times as you want, and the message can be split into as few or many |
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334 | pieces as required without affecting the results, with one |
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335 | exception: All except the last call to "crypt" needs to pass in a |
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336 | multiple of 64 octets. The last call to "crypt" does not have this |
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337 | limitation. |
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338 | |
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339 | $cipher->crypt_inplace ($cleartext_or_ciphertext) |
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340 | Same as "crypt", except it *modifies the argument in-place*. |
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341 | |
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342 | THE Crypt::Spritz::PRNG CLASS |
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343 | This class implements a Pseudorandom Number Generatore (PRNG), sometimes |
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344 | also called a Deterministic Random Bit Generator (DRBG). In fact, it is |
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345 | even cryptographically secure, making it a CSPRNG. |
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346 | |
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347 | Typical usage as a random number generator involves creating a PRNG |
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348 | object with a seed of your choice, and then fetching randomness via |
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349 | "get": |
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350 | |
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351 | # create a PRNG object, use a seed string of your choice |
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352 | my $prng = new Crypt::Spritz::PRNG $seed; |
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353 | |
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354 | # now call get as many times as you wish to get binary randomness |
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355 | my $some_randomness = $prng->get (17); |
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356 | my moree_randomness = $prng->get (5000); |
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357 | ... |
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358 | |
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359 | Typical usage as a cryptographically secure random number generator is |
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360 | to feed in some secret entropy (32 octets/256 bits are commonly |
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361 | considered enough), for example from "/dev/random" or "/dev/urandom", |
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362 | and then generate some key material. |
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363 | |
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364 | # create a PRNG object |
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365 | my $prng = new Crypt::Spritz::PRNG; |
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366 | |
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367 | # seed some entropy (either via ->add or in the constructor) |
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368 | $prng->add ($some_secret_highly_entropic_string); |
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369 | |
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370 | # now call get as many times as you wish to get |
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371 | # hard to guess binary randomness |
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372 | my $key1 = $prng->get (32); |
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373 | my $key2 = $prng->get (16); |
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374 | ... |
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375 | |
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376 | # for long running programs, it is advisable to |
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377 | # reseed the PRNG from time to time with new entropy |
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378 | $prng->add ($some_more_entropy); |
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379 | |
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380 | $prng = new Crypt::Spritz::PRNG [$seed] |
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381 | Creates a new random number generator object. If $seed is given, |
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382 | then the $seed is added to the internal state as if by a call to |
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383 | "add". |
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384 | |
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385 | $prng->add ($entropy) |
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386 | Adds entropy to the internal state, thereby hopefully making it |
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387 | harder to guess. Good sources for entropy are irregular hardware |
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388 | events, or randomness provided by "/dev/urandom" or "/dev/random". |
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389 | |
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390 | The design of the Spritz PRNG should make it strong against attacks |
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391 | where the attacker controls all the entropy, so it should be safe to |
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392 | add entropy from untrusted sources - more is better than less if you |
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393 | need a CSPRNG. |
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394 | |
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395 | For use as PRNG, of course, this matters very little. |
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396 | |
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397 | $octets = $prng->get ($length) |
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398 | Generates and returns $length random octets as a string. |
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399 | |
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400 | SEE ALSO |
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401 | <http://people.csail.mit.edu/rivest/pubs/RS14.pdf>. |
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402 | |
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403 | SECURITY CONSIDERATIONS |
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404 | I also cannot give any guarantees for security, Spritz is a very new |
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405 | cryptographic algorithm, and when this module was written, almost |
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406 | completely unproven. |
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407 | |
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408 | AUTHOR |
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409 | Marc Lehmann <schmorp@schmorp.de> |
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410 | http://software.schmorp.de/pkg/Crypt-Spritz |
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411 | |
