Mercurial > dropbear
view libtomcrypt/notes/tech0003.txt @ 1855:35d504d59c05
Implement server-side support for sk-ecdsa U2F-backed keys (#142)
* Implement server-side support for sk-ecdsa U2F-backed keys
* Fix out-of-bounds read on normal ecdsa-sha2-[identifier] keys
* Fix one more potential out-of-bounds read
* Check if nistp256 curve is used in sk-ecdsa-sha2- key
It's the only allowed curve per PROTOCOL.u2f specification
* Implement server-side support for sk-ed25519 FIDO2-backed keys
* Keys with type sk-* make no sense as host keys, so they should be
disabled
* fix typo
* Make sk-ecdsa call buf_ecdsa_verify
This reduces code duplication, the SK code just handles the
different message format.
* Reduce sk specific code
The application id can be stored in signkey, then we don't need
to call sk-specific functions from svr-authpubkey
* Remove debugging output, which causes compilation errors with DEBUG_TRACE disabled
* Proper cleanup of sk_app
Co-authored-by: Matt Johnston <[email protected]>
author | egor-duda <egor-duda@users.noreply.github.com> |
---|---|
date | Sat, 22 Jan 2022 16:53:04 +0300 |
parents | 6dba84798cd5 |
children |
line wrap: on
line source
Tech Note 0003 Minimizing Memory Usage Tom St Denis Introduction ------------ For the most part the library can get by with around 20KB of stack and about 32KB of heap even if you use the public key functions. If all you plan on using are the hashes and ciphers than only about 1KB of stack is required and no heap. To save space all of the symmetric key scheduled keys are stored in a union called "symmetric_key". This means the size of a symmetric_key is the size of the largest scheduled key. By removing the ciphers you don't use from the build you can minimize the size of this structure. For instance, by removing both Twofish and Blowfish the size reduces to 768 bytes from the 4,256 bytes it would have been (on a 32-bit platform). Or if you remove Blowfish and use Twofish with TWOFISH_SMALL defined its still 768 bytes. Even at its largest the structure is only 4KB which is normally not a problem for any platform. Cipher Name | Size of scheduled key (bytes) | ------------+-------------------------------| Twofish | 4,256 | Blowfish | 4,168 | 3DES | 768 | SAFER+ | 532 | Serpent | 528 | Rijndael | 516 | XTEA | 256 | RC2 | 256 | DES | 256 | SAFER [#] | 217 | RC5 | 204 | Twofish [*] | 193 | RC6 | 176 | CAST5 | 132 | Noekeon | 32 | Skipjack | 10 | ------------+-------------------------------/ Memory used per cipher on a 32-bit platform. [*] For Twofish with TWOFISH_SMALL defined [#] For all 64-bit SAFER ciphers. Noekeon is a fairly fast cipher and uses very little memory. Ideally in low-ram platforms all other ciphers should be left undefined and Noekeon should remain. While Noekeon is generally considered a secure block cipher (it is insecure as a hash) CAST5 is perhaps a "runner-up" choice. CAST5 has been around longer (it is also known as CAST-128) and is fairly fast as well. You can easily accomplish this via the "config.pl" script. Simply answer "n" to all of the ciphers except the one you want and then rebuild the library. [or you can hand edit tomcrypt_custom.h]