c760149f |
1 | /* -*-c-*- |
2 | * |
3 | * $Id: rsa-priv.c,v 1.1 2000/07/01 11:23:20 mdw Exp $ |
4 | * |
5 | * RSA private-key operations |
6 | * |
7 | * (c) 1999 Straylight/Edgeware |
8 | */ |
9 | |
10 | /*----- Licensing notice --------------------------------------------------* |
11 | * |
12 | * This file is part of Catacomb. |
13 | * |
14 | * Catacomb is free software; you can redistribute it and/or modify |
15 | * it under the terms of the GNU Library General Public License as |
16 | * published by the Free Software Foundation; either version 2 of the |
17 | * License, or (at your option) any later version. |
18 | * |
19 | * Catacomb is distributed in the hope that it will be useful, |
20 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
21 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
22 | * GNU Library General Public License for more details. |
23 | * |
24 | * You should have received a copy of the GNU Library General Public |
25 | * License along with Catacomb; if not, write to the Free |
26 | * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, |
27 | * MA 02111-1307, USA. |
28 | */ |
29 | |
30 | /*----- Revision history --------------------------------------------------* |
31 | * |
32 | * $Log: rsa-priv.c,v $ |
33 | * Revision 1.1 2000/07/01 11:23:20 mdw |
34 | * Renamed from `rsa-decrypt', since the name was no longer appropriate. |
35 | * Add functions for doing padded RSA decryption and signing. |
36 | * |
37 | * --- Previous lives as rsa-decrypt.c --- |
38 | * |
39 | * Revision 1.2 2000/06/17 11:57:56 mdw |
40 | * Improve bulk performance by making better use of Montgomery |
41 | * multiplication and separating out initialization and finalization from |
42 | * the main code. |
43 | * |
44 | * Revision 1.1 1999/12/22 15:50:45 mdw |
45 | * Initial RSA support. |
46 | * |
47 | */ |
48 | |
49 | /*----- Header files ------------------------------------------------------*/ |
50 | |
51 | #include <mLib/alloc.h> |
52 | #include <mLib/bits.h> |
53 | #include <mLib/dstr.h> |
54 | |
55 | #include "mp.h" |
56 | #include "mpmont.h" |
57 | #include "mprand.h" |
58 | #include "rsa.h" |
59 | |
60 | /*----- Public key operations ---------------------------------------------*/ |
61 | |
62 | /* --- @rsa_privcreate@ --- * |
63 | * |
64 | * Arguments: @rsa_privctx *rd@ = pointer to an RSA private key context |
65 | * @rsa_priv *rp@ = pointer to RSA private key |
66 | * @grand *r@ = pointer to random number source for blinding |
67 | * |
68 | * Returns: --- |
69 | * |
70 | * Use: Initializes an RSA private-key context. Keeping a context |
71 | * for several decryption or signing operations provides a minor |
72 | * performance benefit. |
73 | * |
74 | * The random number source may be null if blinding is not |
75 | * desired. This improves decryption speed, at the risk of |
76 | * permitting timing attacks. |
77 | */ |
78 | |
79 | void rsa_privcreate(rsa_privctx *rd, rsa_priv *rp, grand *r) |
80 | { |
81 | rd->rp = rp; |
82 | rd->r = r; |
83 | if (r) |
84 | mpmont_create(&rd->nm, rp->n); |
85 | mpmont_create(&rd->pm, rp->p); |
86 | mpmont_create(&rd->qm, rp->q); |
87 | } |
88 | |
89 | /* --- @rsa_privdestroy@ --- * |
90 | * |
91 | * Arguments: @rsa_privctx *rd@ = pointer to an RSA decryption context |
92 | * |
93 | * Returns: --- |
94 | * |
95 | * Use: Destroys an RSA decryption context. |
96 | */ |
97 | |
98 | void rsa_privdestroy(rsa_privctx *rd) |
99 | { |
100 | if (rd->r) |
101 | mpmont_destroy(&rd->nm); |
102 | mpmont_destroy(&rd->pm); |
103 | mpmont_destroy(&rd->qm); |
104 | } |
105 | |
106 | /* --- @rsa_privop@ --- * |
107 | * |
108 | * Arguments: @rsa_privctx *rd@ = pointer to RSA private key context |
109 | * @mp *d@ = destination |
110 | * @mp *c@ = input message |
111 | * |
112 | * Returns: The transformed output message. |
113 | * |
114 | * Use: Performs an RSA private key operation. This function takes |
115 | * advantage of knowledge of the key factors in order to speed |
116 | * up decryption. It also blinds the ciphertext prior to |
117 | * decryption and unblinds it afterwards to thwart timing |
118 | * attacks. |
119 | */ |
120 | |
121 | mp *rsa_privop(rsa_privctx *rd, mp *d, mp *c) |
122 | { |
123 | mp *ki = MP_NEW; |
124 | rsa_priv *rp = rd->rp; |
125 | |
126 | /* --- If so desired, set up a blinding constant --- * |
127 | * |
128 | * Choose a constant %$k$% relatively prime to the modulus %$m$%. Compute |
129 | * %$c' = c k^e \bmod n$%, and %$k^{-1} \bmod n$%. Don't bother with the |
130 | * CRT stuff here because %$e$% is chosen to be small. |
131 | */ |
132 | |
133 | c = MP_COPY(c); |
134 | if (rd->r) { |
135 | mp *k = MP_NEWSEC, *g = MP_NEW; |
136 | |
137 | do { |
138 | k = mprand_range(k, rp->n, rd->r, 0); |
139 | mp_gcd(&g, 0, &ki, rp->n, k); |
140 | } while (MP_CMP(g, !=, MP_ONE)); |
141 | k = mpmont_expr(&rd->nm, k, k, rp->e); |
142 | c = mpmont_mul(&rd->nm, c, c, k); |
143 | mp_drop(k); |
144 | mp_drop(g); |
145 | } |
146 | |
147 | /* --- Do the actual modular exponentiation --- * |
148 | * |
149 | * Use a slightly hacked version of the Chinese Remainder Theorem stuff. |
150 | * |
151 | * Let %$q' = q^{-1} \bmod p$%. Then note that |
152 | * %$c^d \equiv q (q'(c_p^{d_p} - c_q^{d_q}) \bmod p) + c_q^{d_q} \pmod n$% |
153 | */ |
154 | |
155 | { |
156 | mp *cp = MP_NEW, *cq = MP_NEW; |
157 | |
158 | /* --- Work out the two halves of the result --- */ |
159 | |
160 | mp_div(0, &cp, c, rp->p); |
161 | cp = mpmont_exp(&rd->pm, cp, cp, rp->dp); |
162 | |
163 | mp_div(0, &cq, c, rp->q); |
164 | cq = mpmont_exp(&rd->qm, cq, cq, rp->dq); |
165 | |
166 | /* --- Combine the halves using the result above --- */ |
167 | |
168 | d = mp_sub(d, cp, cq); |
169 | mp_div(0, &d, d, rp->p); |
170 | d = mpmont_mul(&rd->pm, d, d, rp->q_inv); |
171 | d = mpmont_mul(&rd->pm, d, d, rd->pm.r2); |
172 | |
173 | d = mp_mul(d, d, rp->q); |
174 | d = mp_add(d, d, cq); |
175 | if (MP_CMP(d, >=, rp->n)) |
176 | d = mp_sub(d, d, rp->n); |
177 | |
178 | /* --- Tidy away temporary variables --- */ |
179 | |
180 | mp_drop(cp); |
181 | mp_drop(cq); |
182 | } |
183 | |
184 | /* --- Finally, possibly remove the blinding factor --- */ |
185 | |
186 | if (ki) { |
187 | d = mpmont_mul(&rd->nm, d, d, ki); |
188 | d = mpmont_mul(&rd->nm, d, d, rd->nm.r2); |
189 | mp_drop(ki); |
190 | } |
191 | |
192 | /* --- Done --- */ |
193 | |
194 | mp_drop(c); |
195 | return (d); |
196 | } |
197 | |
198 | /* --- @rsa_qprivop@ --- * |
199 | * |
200 | * Arguments: @rsa_priv *rp@ = pointer to RSA parameters |
201 | * @mp *d@ = destination |
202 | * @mp *c@ = input message |
203 | * @grand *r@ = pointer to random number source for blinding |
204 | * |
205 | * Returns: Correctly transformed output message |
206 | * |
207 | * Use: Performs an RSA private key operation, very carefully. |
208 | */ |
209 | |
210 | mp *rsa_qprivop(rsa_priv *rp, mp *d, mp *c, grand *r) |
211 | { |
212 | rsa_privctx rd; |
213 | rsa_privcreate(&rd, rp, r); |
214 | d = rsa_privop(&rd, d, c); |
215 | rsa_privdestroy(&rd); |
216 | return (d); |
217 | } |
218 | |
219 | /*----- Operations with padding -------------------------------------------*/ |
220 | |
221 | /* --- @rsa_sign@ --- * |
222 | * |
223 | * Arguments: @rsa_privctx *rp@ = pointer to an RSA private key context |
224 | * @const void *m@ = pointer to input message |
225 | * @size_t sz@ = size of input message |
226 | * @dstr *d@ = pointer to output string |
227 | * @rsa_encodeproc e@ = encoding procedure |
228 | * @void *earg@ = argument pointer for encoding procedure |
229 | * |
230 | * Returns: The length of the output string if successful, negative on |
231 | * failure. |
232 | * |
233 | * Use: Computes an RSA digital signature. |
234 | */ |
235 | |
236 | int rsa_sign(rsa_privctx *rp, const void *m, size_t sz, |
237 | dstr *d, rsa_encodeproc e, void *earg) |
238 | { |
239 | mp *x; |
240 | size_t n = mp_octets(rp->rp->n); |
241 | octet *p; |
242 | int rc; |
243 | |
244 | /* --- Sort out some space --- */ |
245 | |
246 | dstr_ensure(d, n); |
247 | p = d->buf + d->len; |
248 | p[0] = 0; |
249 | |
250 | /* --- Do the packing --- */ |
251 | |
252 | if ((rc = e(m, sz, p, n, earg)) < 0) |
253 | return (rc); |
254 | |
255 | /* --- Do the encryption --- */ |
256 | |
257 | x = mp_loadb(MP_NEWSEC, p, n); |
258 | x = rsa_privop(rp, x, x); |
259 | mp_storeb(x, p, n); |
260 | d->len += n; |
261 | mp_drop(x); |
262 | return (n); |
263 | } |
264 | |
265 | /* --- @rsa_decrypt@ --- * |
266 | * |
267 | * Arguments: @rsa_privctx *rp@ = pointer to an RSA private key context |
268 | * @const void *m@ = pointer to input message |
269 | * @size_t sz@ = size of input message |
270 | * @dstr *d@ = pointer to output string |
271 | * @rsa_decodeproc e@ = decoding procedure |
272 | * @void *earg@ = argument pointer for decoding procedure |
273 | * |
274 | * Returns: The length of the output string if successful, negative on |
275 | * failure. |
276 | * |
277 | * Use: Does RSA signature verification. |
278 | */ |
279 | |
280 | int rsa_decrypt(rsa_privctx *rp, const void *m, size_t sz, |
281 | dstr *d, rsa_decodeproc e, void *earg) |
282 | { |
283 | mp *x; |
284 | size_t n = mp_octets(rp->rp->n); |
285 | octet *p; |
286 | int rc; |
287 | |
288 | /* --- Do the exponentiation --- */ |
289 | |
290 | p = x_alloc(d->a, n); |
291 | x = mp_loadb(MP_NEW, m, sz); |
292 | x = rsa_privop(rp, x, x); |
293 | mp_storeb(x, p, n); |
294 | mp_drop(x); |
295 | |
296 | /* --- Do the decoding --- */ |
297 | |
298 | rc = e(p, n, d, earg); |
299 | x_free(d->a, p); |
300 | return (rc); |
301 | } |
302 | |
303 | /*----- That's all, folks -------------------------------------------------*/ |