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annotate libtomcrypt/notes/tech0003.txt @ 1672:3a97f14c0235

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Add Chacha20-Poly1305, AES128-GCM and AES256-GCM support (#93) * Add Chacha20-Poly1305 authenticated encryption * Add general AEAD approach. * Add [email protected] algo using LibTomCrypt chacha and poly1305 routines. Chacha20-Poly1305 is generally faster than AES256 on CPU w/o dedicated AES instructions, having the same key size. Compiling in will add ~5,5kB to binary size on x86-64. function old new delta chacha_crypt - 1397 +1397 _poly1305_block - 608 +608 poly1305_done - 595 +595 dropbear_chachapoly_crypt - 457 +457 .rodata 26976 27392 +416 poly1305_process - 290 +290 poly1305_init - 221 +221 chacha_setup - 218 +218 encrypt_packet 1068 1270 +202 dropbear_chachapoly_getlength - 147 +147 decrypt_packet 756 897 +141 chacha_ivctr64 - 137 +137 read_packet 543 637 +94 dropbear_chachapoly_start - 94 +94 read_kex_algos 792 880 +88 chacha_keystream - 69 +69 dropbear_mode_chachapoly - 48 +48 sshciphers 280 320 +40 dropbear_mode_none 24 48 +24 dropbear_mode_ctr 24 48 +24 dropbear_mode_cbc 24 48 +24 dropbear_chachapoly_mac - 24 +24 dropbear_chachapoly - 24 +24 gen_new_keys 848 854 +6 ------------------------------------------------------------------------------ (add/remove: 14/0 grow/shrink: 10/0 up/down: 5388/0) Total: 5388 bytes * Add AES128-GCM and AES256-GCM authenticated encryption * Add general AES-GCM mode. * Add [email protected] and [email protected] algo using LibTomCrypt gcm routines. AES-GCM is combination of AES CTR mode and GHASH, slower than AES-CTR on CPU w/o dedicated AES/GHASH instructions therefore disabled by default. Compiling in will add ~6kB to binary size on x86-64. function old new delta gcm_process - 1060 +1060 .rodata 26976 27808 +832 gcm_gf_mult - 820 +820 gcm_add_aad - 660 +660 gcm_shift_table - 512 +512 gcm_done - 471 +471 gcm_add_iv - 384 +384 gcm_init - 347 +347 dropbear_gcm_crypt - 309 +309 encrypt_packet 1068 1270 +202 decrypt_packet 756 897 +141 gcm_reset - 118 +118 read_packet 543 637 +94 read_kex_algos 792 880 +88 sshciphers 280 360 +80 gcm_mult_h - 80 +80 dropbear_gcm_start - 62 +62 dropbear_mode_gcm - 48 +48 dropbear_mode_none 24 48 +24 dropbear_mode_ctr 24 48 +24 dropbear_mode_cbc 24 48 +24 dropbear_ghash - 24 +24 dropbear_gcm_getlength - 24 +24 gen_new_keys 848 854 +6 ------------------------------------------------------------------------------ (add/remove: 14/0 grow/shrink: 10/0 up/down: 6434/0) Total: 6434 bytes
author Vladislav Grishenko <themiron@users.noreply.github.com>
date Mon, 25 May 2020 20:50:25 +0500
parents 6dba84798cd5
children
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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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5 Introduction
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6 ------------
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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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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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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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37 Skipjack | 10 |
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38 ------------+-------------------------------/
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39 Memory used per cipher on a 32-bit platform.
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41 [*] For Twofish with TWOFISH_SMALL defined
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42 [#] For all 64-bit SAFER ciphers.
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44 Noekeon is a fairly fast cipher and uses very little memory. Ideally in low-ram platforms all other ciphers should be
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45 left undefined and Noekeon should remain. While Noekeon is generally considered a secure block cipher (it is insecure
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46 as a hash) CAST5 is perhaps a "runner-up" choice. CAST5 has been around longer (it is also known as CAST-128) and is
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47 fairly fast as well.
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49 You can easily accomplish this via the "config.pl" script. Simply answer "n" to all of the ciphers except the one you want
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6dba84798cd5 Update to libtomcrypt 1.18.1, merged with Dropbear changes
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50 and then rebuild the library. [or you can hand edit tomcrypt_custom.h]
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