nhyatt/putty-source
1
0
Fork 0
mirror of https://git.tartarus.org/simon/putty.git synced 2025-07-02 03:52:49 -05:00
Code Issues Projects Releases Wiki Activity

Make mp_unsafe_mod_integer not be unsafe.

Browse Source 
I've moved it from mpunsafe.c into the main mpint.c, and renamed it
mp_mod_known_integer, because now it manages to avoid leaking
information about the mp_int you give it.

It can still potentially leak information about the small _modulus_
integer - hence the word 'known' in the new function name. This won't
be a problem in any existing use of the function, because it's used
during prime generation to check divisibility by all the small primes,
and optionally also check for residue 1 mod the RSA public exponent.
But all those values are well known and not secret.

This removes one source of side-channel leakage from prime generation.
This commit is contained in:
Simon Tatham
2021-08-27 17:43:40 +01:00
parent 22fab78376
commit 59409d0947
5 changed files with 90 additions and 20 deletions
Download Patch File Download Diff File Expand all files Collapse all files

10
keygen/mpunsafe.c
View File

@ -45,13 +45,3 @@ mp_int *mp_unsafe_copy(mp_int *x)
mp_copy_into(copy, x);
return copy;
}
uint32_t mp_unsafe_mod_integer(mp_int *x, uint32_t modulus)
{
uint64_t accumulator = 0;
for (size_t i = mp_max_bytes(x); i-- > 0 ;) {
accumulator = 0x100 * accumulator + mp_get_byte(x, i);
accumulator %= modulus;
}
return accumulator;
}