src/TortoisePlink/mpunsafe.h

   1 /*
   2  * mpunsafe.h: functions that deal with mp_ints in ways that are *not*
   3  * expected to be constant-time. Used during key generation, in which
   4  * constant run time is a lost cause anyway.
   5  *
   6  * These functions are in a separate header, so that you can easily
   7  * check that you're not calling them in the wrong context. They're
   8  * also defined in a separate source file, which is only linked in to
   9  * the key generation tools. Furthermore, that source file also
  10  * defines a global symbol that intentionally conflicts with one
  11  * defined in the SSH client code, so that any attempt to put these
  12  * functions into the same binary as the live SSH client
  13  * implementation will cause a link-time failure. They should only be
  14  * linked into PuTTYgen and auxiliary test programs.
  15  *
  16  * Also, just in case those precautions aren't enough, all the unsafe
  17  * functions have 'unsafe' in the name.
  18  */
  19
  20 #ifndef PUTTY_MPINT_UNSAFE_H
  21 #define PUTTY_MPINT_UNSAFE_H
  22
  23 /*
  24  * The most obvious unsafe thing you want to do with an mp_int is to
  25  * get rid of leading zero words in its representation, so that its
  26  * nominal size is as close as possible to its true size, and you
  27  * don't waste any time processing it.
  28  *
  29  * mp_unsafe_shrink performs this operation in place, mutating the
  30  * size field of the mp_int it's given. It returns the same pointer it
  31  * was given.
  32  *
  33  * mp_unsafe_copy leaves the original mp_int alone and makes a new one
  34  * with the minimal size.
  35  */
  36 mp_int *mp_unsafe_shrink(mp_int *m);
  37 mp_int *mp_unsafe_copy(mp_int *m);
  38
  39 /*
  40  * Compute the residue of x mod m. This is implemented in the most
  41  * obvious way using the C % operator, which won't be constant-time on
  42  * many C implementations.
  43  */
  44 uint32_t mp_unsafe_mod_integer(mp_int *x, uint32_t m);
  45
  46 #endif /* PUTTY_MPINT_UNSAFE_H */