Mercurial > dropbear
annotate libtomcrypt/notes/tech0003.txt @ 1575:e75dab5bec71
some linting after fuzz merge (#60)
* fix prototype
* remove extra comma
* use m_free after m_strdup
author | François Perrad <francois.perrad@gadz.org> |
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date | Sat, 03 Mar 2018 04:06:45 +0100 |
parents | 6dba84798cd5 |
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1 Tech Note 0003 |
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2 Minimizing Memory Usage |
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3 Tom St Denis |
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4 |
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5 Introduction |
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6 ------------ |
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7 |
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8 For the most part the library can get by with around 20KB of stack and about 32KB of heap even if you use the |
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9 public key functions. If all you plan on using are the hashes and ciphers than only about 1KB of stack is required |
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10 and no heap. |
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11 |
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12 To save space all of the symmetric key scheduled keys are stored in a union called "symmetric_key". This means the |
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13 size of a symmetric_key is the size of the largest scheduled key. By removing the ciphers you don't use from |
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14 the build you can minimize the size of this structure. For instance, by removing both Twofish and Blowfish the |
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15 size reduces to 768 bytes from the 4,256 bytes it would have been (on a 32-bit platform). Or if you remove |
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16 Blowfish and use Twofish with TWOFISH_SMALL defined its still 768 bytes. Even at its largest the structure is only |
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17 4KB which is normally not a problem for any platform. |
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18 |
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19 |
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20 Cipher Name | Size of scheduled key (bytes) | |
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21 ------------+-------------------------------| |
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22 Twofish | 4,256 | |
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23 Blowfish | 4,168 | |
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24 3DES | 768 | |
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25 SAFER+ | 532 | |
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26 Serpent | 528 | |
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27 Rijndael | 516 | |
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28 XTEA | 256 | |
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29 RC2 | 256 | |
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30 DES | 256 | |
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31 SAFER [#] | 217 | |
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32 RC5 | 204 | |
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33 Twofish [*] | 193 | |
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34 RC6 | 176 | |
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35 CAST5 | 132 | |
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36 Noekeon | 32 | |
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