Mercurial > dropbear
view libtommath/bn_mp_montgomery_reduce.c @ 1499:2d450c1056e3
options: Complete the transition to numeric toggles (`#if')
For the sake of review, this commit alters only the code; the affiliated
comments within the source files also need to be updated, but doing so
now would obscure the operational changes that have been made here.
* All on/off options have been switched to the numeric `#if' variant;
that is the only way to make this `default_options.h.in' thing work
in a reasonable manner.
* There is now some very minor compile-time checking of the user's
choice of options.
* NO_FAST_EXPTMOD doesn't seem to be used, so it has been removed.
* ENABLE_USER_ALGO_LIST was supposed to be renamed DROPBEAR_USER_ALGO_LIST,
and this commit completes that work.
* DROPBEAR_FUZZ seems to be a relatively new, as-yet undocumented option,
which was added by the following commit:
commit 6e0b539e9ca0b5628c6c5a3d118ad6a2e79e8039
Author: Matt Johnston <[email protected]>
Date: Tue May 23 22:29:21 2017 +0800
split out checkpubkey_line() separately
It has now been added to `sysoptions.h' and defined as `0' by default.
* The configuration option `DROPBEAR_PASSWORD_ENV' is no longer listed in
`default_options.h.in'; it is no longer meant to be set by the user, and
is instead left to be defined in `sysoptions.h' (where it was already being
defined) as merely the name of the environment variable in question:
DROPBEAR_PASSWORD
To enable or disable use of that environment variable, the user must now
toggle `DROPBEAR_USE_DROPBEAR_PASSWORD'.
* The sFTP support is now toggled by setting `DROPBEAR_SFTPSERVER', and the
path of the sFTP server program is set independently through the usual
SFTPSERVER_PATH.
author | Michael Witten <mfwitten@gmail.com> |
---|---|
date | Thu, 20 Jul 2017 19:38:26 +0000 |
parents | 8bba51a55704 |
children | f52919ffd3b1 |
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line source
#include <tommath_private.h> #ifdef BN_MP_MONTGOMERY_REDUCE_C /* LibTomMath, multiple-precision integer library -- Tom St Denis * * LibTomMath is a library that provides multiple-precision * integer arithmetic as well as number theoretic functionality. * * The library was designed directly after the MPI library by * Michael Fromberger but has been written from scratch with * additional optimizations in place. * * The library is free for all purposes without any express * guarantee it works. * * Tom St Denis, [email protected], http://libtom.org */ /* computes xR**-1 == x (mod N) via Montgomery Reduction */ int mp_montgomery_reduce (mp_int * x, mp_int * n, mp_digit rho) { int ix, res, digs; mp_digit mu; /* can the fast reduction [comba] method be used? * * Note that unlike in mul you're safely allowed *less* * than the available columns [255 per default] since carries * are fixed up in the inner loop. */ digs = (n->used * 2) + 1; if ((digs < MP_WARRAY) && (n->used < (1 << ((CHAR_BIT * sizeof(mp_word)) - (2 * DIGIT_BIT))))) { return fast_mp_montgomery_reduce (x, n, rho); } /* grow the input as required */ if (x->alloc < digs) { if ((res = mp_grow (x, digs)) != MP_OKAY) { return res; } } x->used = digs; for (ix = 0; ix < n->used; ix++) { /* mu = ai * rho mod b * * The value of rho must be precalculated via * montgomery_setup() such that * it equals -1/n0 mod b this allows the * following inner loop to reduce the * input one digit at a time */ mu = (mp_digit) (((mp_word)x->dp[ix] * (mp_word)rho) & MP_MASK); /* a = a + mu * m * b**i */ { int iy; mp_digit *tmpn, *tmpx, u; mp_word r; /* alias for digits of the modulus */ tmpn = n->dp; /* alias for the digits of x [the input] */ tmpx = x->dp + ix; /* set the carry to zero */ u = 0; /* Multiply and add in place */ for (iy = 0; iy < n->used; iy++) { /* compute product and sum */ r = ((mp_word)mu * (mp_word)*tmpn++) + (mp_word) u + (mp_word) *tmpx; /* get carry */ u = (mp_digit)(r >> ((mp_word) DIGIT_BIT)); /* fix digit */ *tmpx++ = (mp_digit)(r & ((mp_word) MP_MASK)); } /* At this point the ix'th digit of x should be zero */ /* propagate carries upwards as required*/ while (u != 0) { *tmpx += u; u = *tmpx >> DIGIT_BIT; *tmpx++ &= MP_MASK; } } } /* at this point the n.used'th least * significant digits of x are all zero * which means we can shift x to the * right by n.used digits and the * residue is unchanged. */ /* x = x/b**n.used */ mp_clamp(x); mp_rshd (x, n->used); /* if x >= n then x = x - n */ if (mp_cmp_mag (x, n) != MP_LT) { return s_mp_sub (x, n, x); } return MP_OKAY; } #endif /* ref: $Format:%D$ */ /* git commit: $Format:%H$ */ /* commit time: $Format:%ai$ */