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Diffstat (limited to 'lib/mpi/mpi-pow.c')
| -rw-r--r-- | lib/mpi/mpi-pow.c | 327 |
1 files changed, 327 insertions, 0 deletions
diff --git a/lib/mpi/mpi-pow.c b/lib/mpi/mpi-pow.c new file mode 100644 index 000000000..d3ca55093 --- /dev/null +++ b/lib/mpi/mpi-pow.c @@ -0,0 +1,327 @@ +/* mpi-pow.c - MPI functions + * Copyright (C) 1994, 1996, 1998, 2000 Free Software Foundation, Inc. + * + * This file is part of GnuPG. + * + * GnuPG is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * GnuPG is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA + * + * Note: This code is heavily based on the GNU MP Library. + * Actually it's the same code with only minor changes in the + * way the data is stored; this is to support the abstraction + * of an optional secure memory allocation which may be used + * to avoid revealing of sensitive data due to paging etc. + * The GNU MP Library itself is published under the LGPL; + * however I decided to publish this code under the plain GPL. + */ + +#include <linux/sched.h> +#include <linux/string.h> +#include "mpi-internal.h" +#include "longlong.h" + +/**************** + * RES = BASE ^ EXP mod MOD + */ +int mpi_powm(MPI res, MPI base, MPI exp, MPI mod) +{ + mpi_ptr_t mp_marker = NULL, bp_marker = NULL, ep_marker = NULL; + struct karatsuba_ctx karactx = {}; + mpi_ptr_t xp_marker = NULL; + mpi_ptr_t tspace = NULL; + mpi_ptr_t rp, ep, mp, bp; + mpi_size_t esize, msize, bsize, rsize; + int msign, bsign, rsign; + mpi_size_t size; + int mod_shift_cnt; + int negative_result; + int assign_rp = 0; + mpi_size_t tsize = 0; /* to avoid compiler warning */ + /* fixme: we should check that the warning is void */ + int rc = -ENOMEM; + + esize = exp->nlimbs; + msize = mod->nlimbs; + size = 2 * msize; + msign = mod->sign; + + rp = res->d; + ep = exp->d; + + if (!msize) + return -EINVAL; + + if (!esize) { + /* Exponent is zero, result is 1 mod MOD, i.e., 1 or 0 + * depending on if MOD equals 1. */ + res->nlimbs = (msize == 1 && mod->d[0] == 1) ? 0 : 1; + if (res->nlimbs) { + if (mpi_resize(res, 1) < 0) + goto enomem; + rp = res->d; + rp[0] = 1; + } + res->sign = 0; + goto leave; + } + + /* Normalize MOD (i.e. make its most significant bit set) as required by + * mpn_divrem. This will make the intermediate values in the calculation + * slightly larger, but the correct result is obtained after a final + * reduction using the original MOD value. */ + mp = mp_marker = mpi_alloc_limb_space(msize); + if (!mp) + goto enomem; + mod_shift_cnt = count_leading_zeros(mod->d[msize - 1]); + if (mod_shift_cnt) + mpihelp_lshift(mp, mod->d, msize, mod_shift_cnt); + else + MPN_COPY(mp, mod->d, msize); + + bsize = base->nlimbs; + bsign = base->sign; + if (bsize > msize) { /* The base is larger than the module. Reduce it. */ + /* Allocate (BSIZE + 1) with space for remainder and quotient. + * (The quotient is (bsize - msize + 1) limbs.) */ + bp = bp_marker = mpi_alloc_limb_space(bsize + 1); + if (!bp) + goto enomem; + MPN_COPY(bp, base->d, bsize); + /* We don't care about the quotient, store it above the remainder, + * at BP + MSIZE. */ + mpihelp_divrem(bp + msize, 0, bp, bsize, mp, msize); + bsize = msize; + /* Canonicalize the base, since we are going to multiply with it + * quite a few times. */ + MPN_NORMALIZE(bp, bsize); + } else + bp = base->d; + + if (!bsize) { + res->nlimbs = 0; + res->sign = 0; + goto leave; + } + + if (res->alloced < size) { + /* We have to allocate more space for RES. If any of the input + * parameters are identical to RES, defer deallocation of the old + * space. */ + if (rp == ep || rp == mp || rp == bp) { + rp = mpi_alloc_limb_space(size); + if (!rp) + goto enomem; + assign_rp = 1; + } else { + if (mpi_resize(res, size) < 0) + goto enomem; + rp = res->d; + } + } else { /* Make BASE, EXP and MOD not overlap with RES. */ + if (rp == bp) { + /* RES and BASE are identical. Allocate temp. space for BASE. */ + BUG_ON(bp_marker); + bp = bp_marker = mpi_alloc_limb_space(bsize); + if (!bp) + goto enomem; + MPN_COPY(bp, rp, bsize); + } + if (rp == ep) { + /* RES and EXP are identical. Allocate temp. space for EXP. */ + ep = ep_marker = mpi_alloc_limb_space(esize); + if (!ep) + goto enomem; + MPN_COPY(ep, rp, esize); + } + if (rp == mp) { + /* RES and MOD are identical. Allocate temporary space for MOD. */ + BUG_ON(mp_marker); + mp = mp_marker = mpi_alloc_limb_space(msize); + if (!mp) + goto enomem; + MPN_COPY(mp, rp, msize); + } + } + + MPN_COPY(rp, bp, bsize); + rsize = bsize; + rsign = bsign; + + { + mpi_size_t i; + mpi_ptr_t xp; + int c; + mpi_limb_t e; + mpi_limb_t carry_limb; + + xp = xp_marker = mpi_alloc_limb_space(2 * (msize + 1)); + if (!xp) + goto enomem; + + negative_result = (ep[0] & 1) && base->sign; + + i = esize - 1; + e = ep[i]; + c = count_leading_zeros(e); + e = (e << c) << 1; /* shift the exp bits to the left, lose msb */ + c = BITS_PER_MPI_LIMB - 1 - c; + + /* Main loop. + * + * Make the result be pointed to alternately by XP and RP. This + * helps us avoid block copying, which would otherwise be necessary + * with the overlap restrictions of mpihelp_divmod. With 50% probability + * the result after this loop will be in the area originally pointed + * by RP (==RES->d), and with 50% probability in the area originally + * pointed to by XP. + */ + + for (;;) { + while (c) { + mpi_ptr_t tp; + mpi_size_t xsize; + + /*if (mpihelp_mul_n(xp, rp, rp, rsize) < 0) goto enomem */ + if (rsize < KARATSUBA_THRESHOLD) + mpih_sqr_n_basecase(xp, rp, rsize); + else { + if (!tspace) { + tsize = 2 * rsize; + tspace = + mpi_alloc_limb_space(tsize); + if (!tspace) + goto enomem; + } else if (tsize < (2 * rsize)) { + mpi_free_limb_space(tspace); + tsize = 2 * rsize; + tspace = + mpi_alloc_limb_space(tsize); + if (!tspace) + goto enomem; + } + mpih_sqr_n(xp, rp, rsize, tspace); + } + + xsize = 2 * rsize; + if (xsize > msize) { + mpihelp_divrem(xp + msize, 0, xp, xsize, + mp, msize); + xsize = msize; + } + + tp = rp; + rp = xp; + xp = tp; + rsize = xsize; + + if ((mpi_limb_signed_t) e < 0) { + /*mpihelp_mul( xp, rp, rsize, bp, bsize ); */ + if (bsize < KARATSUBA_THRESHOLD) { + mpi_limb_t tmp; + if (mpihelp_mul + (xp, rp, rsize, bp, bsize, + &tmp) < 0) + goto enomem; + } else { + if (mpihelp_mul_karatsuba_case + (xp, rp, rsize, bp, bsize, + &karactx) < 0) + goto enomem; + } + + xsize = rsize + bsize; + if (xsize > msize) { + mpihelp_divrem(xp + msize, 0, + xp, xsize, mp, + msize); + xsize = msize; + } + + tp = rp; + rp = xp; + xp = tp; + rsize = xsize; + } + e <<= 1; + c--; + cond_resched(); + } + + i--; + if (i < 0) + break; + e = ep[i]; + c = BITS_PER_MPI_LIMB; + } + + /* We shifted MOD, the modulo reduction argument, left MOD_SHIFT_CNT + * steps. Adjust the result by reducing it with the original MOD. + * + * Also make sure the result is put in RES->d (where it already + * might be, see above). + */ + if (mod_shift_cnt) { + carry_limb = + mpihelp_lshift(res->d, rp, rsize, mod_shift_cnt); + rp = res->d; + if (carry_limb) { + rp[rsize] = carry_limb; + rsize++; + } + } else { + MPN_COPY(res->d, rp, rsize); + rp = res->d; + } + + if (rsize >= msize) { + mpihelp_divrem(rp + msize, 0, rp, rsize, mp, msize); + rsize = msize; + } + + /* Remove any leading zero words from the result. */ + if (mod_shift_cnt) + mpihelp_rshift(rp, rp, rsize, mod_shift_cnt); + MPN_NORMALIZE(rp, rsize); + } + + if (negative_result && rsize) { + if (mod_shift_cnt) + mpihelp_rshift(mp, mp, msize, mod_shift_cnt); + mpihelp_sub(rp, mp, msize, rp, rsize); + rsize = msize; + rsign = msign; + MPN_NORMALIZE(rp, rsize); + } + res->nlimbs = rsize; + res->sign = rsign; + +leave: + rc = 0; +enomem: + mpihelp_release_karatsuba_ctx(&karactx); + if (assign_rp) + mpi_assign_limb_space(res, rp, size); + if (mp_marker) + mpi_free_limb_space(mp_marker); + if (bp_marker) + mpi_free_limb_space(bp_marker); + if (ep_marker) + mpi_free_limb_space(ep_marker); + if (xp_marker) + mpi_free_limb_space(xp_marker); + if (tspace) + mpi_free_limb_space(tspace); + return rc; +} +EXPORT_SYMBOL_GPL(mpi_powm); |