1 // SPDX-License-Identifier: GPL-2.0-or-later 1
2 /* mpi-pow.c - MPI functions
3 * Copyright (C) 1994, 1996, 1998, 2000 F
4 *
5 * This file is part of GnuPG.
6 *
7 * Note: This code is heavily based on the GNU
8 * Actually it's the same code with only
9 * way the data is stored; this is to su
10 * of an optional secure memory allocati
11 * to avoid revealing of sensitive data
12 * The GNU MP Library itself is publishe
13 * however I decided to publish this cod
14 */
15
16 #include <linux/sched.h>
17 #include <linux/string.h>
18 #include "mpi-internal.h"
19 #include "longlong.h"
20
21 /****************
22 * RES = BASE ^ EXP mod MOD
23 */
24 int mpi_powm(MPI res, MPI base, MPI exp, MPI m
25 {
26 mpi_ptr_t mp_marker = NULL, bp_marker
27 struct karatsuba_ctx karactx = {};
28 mpi_ptr_t xp_marker = NULL;
29 mpi_ptr_t tspace = NULL;
30 mpi_ptr_t rp, ep, mp, bp;
31 mpi_size_t esize, msize, bsize, rsize;
32 int msign, bsign, rsign;
33 mpi_size_t size;
34 int mod_shift_cnt;
35 int negative_result;
36 int assign_rp = 0;
37 mpi_size_t tsize = 0; /* to avoid co
38 /* fixme: we should check that the war
39 int rc = -ENOMEM;
40
41 esize = exp->nlimbs;
42 msize = mod->nlimbs;
43 size = 2 * msize;
44 msign = mod->sign;
45
46 rp = res->d;
47 ep = exp->d;
48
49 if (!msize)
50 return -EINVAL;
51
52 if (!esize) {
53 /* Exponent is zero, result is
54 * depending on if MOD equals
55 res->nlimbs = (msize == 1 && m
56 if (res->nlimbs) {
57 if (mpi_resize(res, 1)
58 goto enomem;
59 rp = res->d;
60 rp[0] = 1;
61 }
62 res->sign = 0;
63 goto leave;
64 }
65
66 /* Normalize MOD (i.e. make its most s
67 * mpn_divrem. This will make the int
68 * slightly larger, but the correct re
69 * reduction using the original MOD va
70 mp = mp_marker = mpi_alloc_limb_space(
71 if (!mp)
72 goto enomem;
73 mod_shift_cnt = count_leading_zeros(mo
74 if (mod_shift_cnt)
75 mpihelp_lshift(mp, mod->d, msi
76 else
77 MPN_COPY(mp, mod->d, msize);
78
79 bsize = base->nlimbs;
80 bsign = base->sign;
81 if (bsize > msize) { /* The base is
82 /* Allocate (BSIZE + 1) with s
83 * (The quotient is (bsize - m
84 bp = bp_marker = mpi_alloc_lim
85 if (!bp)
86 goto enomem;
87 MPN_COPY(bp, base->d, bsize);
88 /* We don't care about the quo
89 * at BP + MSIZE. */
90 mpihelp_divrem(bp + msize, 0,
91 bsize = msize;
92 /* Canonicalize the base, sinc
93 * quite a few times. */
94 MPN_NORMALIZE(bp, bsize);
95 } else
96 bp = base->d;
97
98 if (!bsize) {
99 res->nlimbs = 0;
100 res->sign = 0;
101 goto leave;
102 }
103
104 if (res->alloced < size) {
105 /* We have to allocate more sp
106 * parameters are identical to
107 * space. */
108 if (rp == ep || rp == mp || rp
109 rp = mpi_alloc_limb_sp
110 if (!rp)
111 goto enomem;
112 assign_rp = 1;
113 } else {
114 if (mpi_resize(res, si
115 goto enomem;
116 rp = res->d;
117 }
118 } else { /* Make BASE,
119 if (rp == bp) {
120 /* RES and BASE are id
121 BUG_ON(bp_marker);
122 bp = bp_marker = mpi_a
123 if (!bp)
124 goto enomem;
125 MPN_COPY(bp, rp, bsize
126 }
127 if (rp == ep) {
128 /* RES and EXP are ide
129 ep = ep_marker = mpi_a
130 if (!ep)
131 goto enomem;
132 MPN_COPY(ep, rp, esize
133 }
134 if (rp == mp) {
135 /* RES and MOD are ide
136 BUG_ON(mp_marker);
137 mp = mp_marker = mpi_a
138 if (!mp)
139 goto enomem;
140 MPN_COPY(mp, rp, msize
141 }
142 }
143
144 MPN_COPY(rp, bp, bsize);
145 rsize = bsize;
146 rsign = bsign;
147
148 {
149 mpi_size_t i;
150 mpi_ptr_t xp;
151 int c;
152 mpi_limb_t e;
153 mpi_limb_t carry_limb;
154
155 xp = xp_marker = mpi_alloc_lim
156 if (!xp)
157 goto enomem;
158
159 negative_result = (ep[0] & 1)
160
161 i = esize - 1;
162 e = ep[i];
163 c = count_leading_zeros(e);
164 e = (e << c) << 1; /* shi
165 c = BITS_PER_MPI_LIMB - 1 - c;
166
167 /* Main loop.
168 *
169 * Make the result be pointed
170 * helps us avoid block copyin
171 * with the overlap restrictio
172 * the result after this loop
173 * by RP (==RES->d), and with
174 * pointed to by XP.
175 */
176
177 for (;;) {
178 while (c) {
179 mpi_size_t xsi
180
181 /*if (mpihelp_
182 if (rsize < KA
183 mpih_s
184 else {
185 if (!t
186
187
188
189
190
191 } else
192
193
194
195
196
197
198 }
199 mpih_s
200 }
201
202 xsize = 2 * rs
203 if (xsize > ms
204 mpihel
205
206 xsize
207 }
208
209 swap(rp, xp);
210 rsize = xsize;
211
212 if ((mpi_limb_
213 /*mpih
214 if (bs
215
216
217
218
219
220 } else
221
222
223
224
225 }
226
227 xsize
228 if (xs
229
230
231
232
233 }
234
235 swap(r
236 rsize
237 }
238 e <<= 1;
239 c--;
240 cond_resched()
241 }
242
243 i--;
244 if (i < 0)
245 break;
246 e = ep[i];
247 c = BITS_PER_MPI_LIMB;
248 }
249
250 /* We shifted MOD, the modulo
251 * steps. Adjust the result b
252 *
253 * Also make sure the result i
254 * might be, see above).
255 */
256 if (mod_shift_cnt) {
257 carry_limb =
258 mpihelp_lshift(res
259 rp = res->d;
260 if (carry_limb) {
261 rp[rsize] = ca
262 rsize++;
263 }
264 } else {
265 MPN_COPY(res->d, rp, r
266 rp = res->d;
267 }
268
269 if (rsize >= msize) {
270 mpihelp_divrem(rp + ms
271 rsize = msize;
272 }
273
274 /* Remove any leading zero wor
275 if (mod_shift_cnt)
276 mpihelp_rshift(rp, rp,
277 MPN_NORMALIZE(rp, rsize);
278 }
279
280 if (negative_result && rsize) {
281 if (mod_shift_cnt)
282 mpihelp_rshift(mp, mp,
283 mpihelp_sub(rp, mp, msize, rp,
284 rsize = msize;
285 rsign = msign;
286 MPN_NORMALIZE(rp, rsize);
287 }
288 res->nlimbs = rsize;
289 res->sign = rsign;
290
291 leave:
292 rc = 0;
293 enomem:
294 mpihelp_release_karatsuba_ctx(&karactx
295 if (assign_rp)
296 mpi_assign_limb_space(res, rp,
297 if (mp_marker)
298 mpi_free_limb_space(mp_marker)
299 if (bp_marker)
300 mpi_free_limb_space(bp_marker)
301 if (ep_marker)
302 mpi_free_limb_space(ep_marker)
303 if (xp_marker)
304 mpi_free_limb_space(xp_marker)
305 if (tspace)
306 mpi_free_limb_space(tspace);
307 return rc;
308 }
309 EXPORT_SYMBOL_GPL(mpi_powm);
310
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