summaryrefslogtreecommitdiffstats
path: root/lib/mpi/mpi-pow.c
diff options
context:
space:
mode:
Diffstat (limited to 'lib/mpi/mpi-pow.c')
-rw-r--r--lib/mpi/mpi-pow.c314
1 files changed, 314 insertions, 0 deletions
diff --git a/lib/mpi/mpi-pow.c b/lib/mpi/mpi-pow.c
new file mode 100644
index 000000000..2fd7a46d5
--- /dev/null
+++ b/lib/mpi/mpi-pow.c
@@ -0,0 +1,314 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* mpi-pow.c - MPI functions
+ * Copyright (C) 1994, 1996, 1998, 2000 Free Software Foundation, Inc.
+ *
+ * This file is part of GnuPG.
+ *
+ * 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);
generated by cgit v1.2.3 (git 2.39.1) at 2024-11-30 02:31:22 +0000