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59409d0947
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.
48 lines
1.2 KiB
C
48 lines
1.2 KiB
C
#include <assert.h>
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#include <limits.h>
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#include <stdio.h>
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#include "defs.h"
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#include "misc.h"
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#include "puttymem.h"
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#include "mpint.h"
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#include "crypto/mpint_i.h"
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/*
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* This global symbol is also defined in ssh/kex2-client.c, to ensure
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* that these unsafe non-constant-time mp_int functions can't end up
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* accidentally linked in to any PuTTY tool that actually makes an SSH
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* client connection.
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*
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* (Only _client_ connections, however. Uppity, being a test server
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* only, is exempt.)
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*/
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const int deliberate_symbol_clash = 12345;
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static size_t mp_unsafe_words_needed(mp_int *x)
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{
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size_t words = x->nw;
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while (words > 1 && !x->w[words-1])
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words--;
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return words;
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}
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mp_int *mp_unsafe_shrink(mp_int *x)
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{
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x->nw = mp_unsafe_words_needed(x);
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/* This potentially leaves some allocated words between the new
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* and old values of x->nw, which won't be wiped by mp_free now
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* that x->nw doesn't mention that they exist. But we've just
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* checked they're all zero, so we don't need to wipe them now
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* either. */
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return x;
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}
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mp_int *mp_unsafe_copy(mp_int *x)
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{
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mp_int *copy = mp_make_sized(mp_unsafe_words_needed(x));
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mp_copy_into(copy, x);
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return copy;
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}
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