src/TortoisePlink/mpunsafe.c

   1 #include <assert.h>
   2 #include <limits.h>
   3 #include <stdio.h>
   4
   5 #include "defs.h"
   6 #include "misc.h"
   7 #include "puttymem.h"
   8
   9 #include "mpint.h"
  10 #include "mpint_i.h"
  11
  12 /*
  13  * This global symbol is also defined in ssh2kex-client.c, to ensure
  14  * that these unsafe non-constant-time mp_int functions can't end up
  15  * accidentally linked in to any PuTTY tool that actually makes an SSH
  16  * client connection.
  17  *
  18  * (Only _client_ connections, however. Uppity, being a test server
  19  * only, is exempt.)
  20  */
  21 const int deliberate_symbol_clash = 12345;
  22
  23 static size_t mp_unsafe_words_needed(mp_int *x)
  24 {
  25     size_t words = x->nw;
  26     while (words > 1 && !x->w[words-1])
  27         words--;
  28     return words;
  29 }
  30
  31 mp_int *mp_unsafe_shrink(mp_int *x)
  32 {
  33     x->nw = mp_unsafe_words_needed(x);
  34     /* This potentially leaves some allocated words between the new
  35      * and old values of x->nw, which won't be wiped by mp_free now
  36      * that x->nw doesn't mention that they exist. But we've just
  37      * checked they're all zero, so we don't need to wipe them now
  38      * either. */
  39     return x;
  40 }
  41
  42 mp_int *mp_unsafe_copy(mp_int *x)
  43 {
  44     mp_int *copy = mp_make_sized(mp_unsafe_words_needed(x));
  45     mp_copy_into(copy, x);
  46     return copy;
  47 }
  48
  49 uint32_t mp_unsafe_mod_integer(mp_int *x, uint32_t modulus)
  50 {
  51     uint64_t accumulator = 0;
  52     for (size_t i = mp_max_bytes(x); i-- > 0 ;) {
  53         accumulator = 0x100 * accumulator + mp_get_byte(x, i);
  54         accumulator %= modulus;
  55     }
  56     return accumulator;
  57 }