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1 | /* -*-c-*- |
2 | * |
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3 | * $Id: dsa-verify.c,v 1.2 1999/11/23 00:20:04 mdw Exp $ |
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4 | * |
5 | * DSA signature verification |
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: dsa-verify.c,v $ |
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33 | * Revision 1.2 1999/11/23 00:20:04 mdw |
34 | * Remove stray debugging code. |
35 | * |
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36 | * Revision 1.1 1999/11/19 19:28:00 mdw |
37 | * Implementation of the Digital Signature Algorithm. |
38 | * |
39 | */ |
40 | |
41 | /*----- Header files ------------------------------------------------------*/ |
42 | |
43 | #include "dsa.h" |
44 | #include "mp.h" |
45 | #include "mpmont.h" |
46 | |
47 | /*----- Main code ---------------------------------------------------------*/ |
48 | |
49 | /* --- @dsa_vrfy@ --- * |
50 | * |
51 | * Arguments: @const dsa_param *dp@ = pointer to DSA parameters |
52 | * @const mp *y@ = public verification key |
53 | * @const mp *m@ = message which was signed |
54 | * @const mp *r, *s@ = the signature |
55 | * |
56 | * Returns: Zero if the signature is a forgery, nonzero if it's valid. |
57 | * |
58 | * Use: Verifies a DSA digital signature. |
59 | */ |
60 | |
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61 | int dsa_vrfy(const dsa_param *dp, const mp *y, |
62 | const mp *m, const mp *r, const mp *s) |
63 | { |
64 | mpmont pm, qm; |
65 | mp *w; |
66 | mpmont_factor f[2]; |
67 | int ok; |
68 | |
69 | /* --- Ensure that all of the signature bits are in range --- */ |
70 | |
71 | if ((r->f | s->f) & MP_NEG) |
72 | return (0); |
73 | if (MP_CMP(r, >=, dp->q) || MP_CMP(s, >=, dp->q)) |
74 | return (0); |
75 | |
76 | /* --- Set up Montgomery contexts --- */ |
77 | |
78 | mpmont_create(&pm, dp->p); |
79 | mpmont_create(&qm, dp->q); |
80 | |
81 | /* --- Compute %$w = s^{-1} \bmod q$% --- */ |
82 | |
83 | { |
84 | mp *z; |
85 | mp_gcd(0, 0, &z, dp->q, (mp *)s); |
86 | w = mpmont_mul(&qm, MP_NEW, z, qm.r2); |
87 | mp_drop(z); |
88 | } |
89 | |
90 | /* --- Compute %$wr%$ and %$wm$% --- */ |
91 | |
92 | f[0].exp = mpmont_mul(&qm, MP_NEW, w, m); |
93 | f[1].exp = mpmont_mul(&qm, MP_NEW, w, r); |
94 | mp_drop(w); |
95 | mpmont_destroy(&qm); |
96 | |
97 | /* --- Do the exponentiation and take residue mod @q@ --- */ |
98 | |
99 | f[0].base = dp->g; |
100 | f[1].base = (mp *)y; |
101 | w = mpmont_mexp(&pm, f, 2); |
102 | mp_div(0, &w, w, dp->q); |
103 | ok = MP_CMP(w, ==, r); |
104 | |
105 | /* --- Tidy up --- */ |
106 | |
107 | mp_drop(w); |
108 | mp_drop(f[0].exp); |
109 | mp_drop(f[1].exp); |
110 | mpmont_destroy(&pm); |
111 | return (ok); |
112 | } |
113 | |
114 | /* --- @dsa_verify@ --- * |
115 | * |
116 | * Arguments: @const dsa_param *dp@ = pointer to DSA parameters |
117 | * @const mp *y@ = public verification key |
118 | * @const void *m@ = pointer to message block |
119 | * @size_t msz@ = size of message block |
120 | * @const void *r@ = pointer to @r@ signature half |
121 | * @size_t rsz@ = size of @r@ |
122 | * @const void *s@ = pointer to @s@ signature half |
123 | * @size_t ssz@ = size of @s@ |
124 | * |
125 | * Returns: Zero if the signature is a forgery, nonzero if it's valid. |
126 | * |
127 | * Use: Verifies a DSA digital signature. |
128 | */ |
129 | |
130 | int dsa_verify(const dsa_param *dp, const mp *y, |
131 | const void *m, size_t msz, |
132 | const void *r, size_t rsz, |
133 | const void *s, size_t ssz) |
134 | { |
135 | mp *mm = mp_loadb(MP_NEW, m, msz); |
136 | mp *rm = mp_loadb(MP_NEW, r, rsz); |
137 | mp *sm = mp_loadb(MP_NEW, s, ssz); |
138 | int ok = dsa_vrfy(dp, y, mm, rm, sm); |
139 | mp_drop(mm); |
140 | mp_drop(rm); |
141 | mp_drop(sm); |
142 | return (ok); |
143 | } |
144 | |
145 | /*----- Test rig ----------------------------------------------------------*/ |
146 | |
147 | #ifdef TEST_RIG |
148 | |
149 | #include <mLib/testrig.h> |
150 | |
151 | #include "sha.h" |
152 | |
153 | static int verify(int good, dstr *v) |
154 | { |
155 | dsa_param dp; |
156 | mp *y; |
157 | sha_ctx c; |
158 | octet hash[SHA_HASHSZ]; |
159 | int ok = 1; |
160 | int rc; |
161 | |
162 | dp.q = *(mp **)v[0].buf; |
163 | dp.p = *(mp **)v[1].buf; |
164 | dp.g = *(mp **)v[2].buf; |
165 | y = *(mp **)v[3].buf; |
166 | |
167 | sha_init(&c); |
168 | sha_hash(&c, v[4].buf, v[4].len); |
169 | sha_done(&c, hash); |
170 | |
171 | rc = dsa_verify(&dp, y, hash, sizeof(hash), |
172 | v[5].buf, v[5].len, v[6].buf, v[6].len); |
173 | |
174 | if (!rc != !good) { |
175 | if (good) |
176 | fputs("\n*** verification failed", stderr); |
177 | else |
178 | fputs("\n*** verification succeeded", stderr); |
179 | fputs("\nq = ", stderr); mp_writefile(dp.q, stderr, 16); |
180 | fputs("\np = ", stderr); mp_writefile(dp.p, stderr, 16); |
181 | fputs("\ng = ", stderr); mp_writefile(dp.g, stderr, 16); |
182 | fputs("\ny = ", stderr); mp_writefile(y, stderr, 16); |
183 | fprintf(stderr, "\nmessage = `%s'", v[4].buf); |
184 | fputs("\nr = ", stderr); type_hex.dump(&v[5], stderr); |
185 | fputs("\ns = ", stderr); type_hex.dump(&v[6], stderr); |
186 | fputc('\n', stderr); |
187 | ok = 0; |
188 | } |
189 | |
190 | mp_drop(dp.p); |
191 | mp_drop(dp.q); |
192 | mp_drop(dp.g); |
193 | mp_drop(y); |
194 | return (ok); |
195 | } |
196 | |
197 | static int vgood(dstr *v) { return verify(1, v); } |
198 | static int vbad(dstr *v) { return verify(0, v); } |
199 | |
200 | static test_chunk tests[] = { |
201 | { "verify-good", vgood, |
202 | { &type_mp, &type_mp, &type_mp, &type_mp, |
203 | &type_string, &type_hex, &type_hex, 0 } }, |
204 | { "verify-bad", vbad, |
205 | { &type_mp, &type_mp, &type_mp, &type_mp, |
206 | &type_string, &type_hex, &type_hex, 0 } }, |
207 | { 0, 0, { 0 } } |
208 | }; |
209 | |
210 | int main(int argc, char *argv[]) |
211 | { |
212 | sub_init(); |
213 | test_run(argc, argv, tests, SRCDIR "/tests/dsa"); |
214 | return (0); |
215 | } |
216 | |
217 | #endif |
218 | |
219 | /*----- That's all, folks -------------------------------------------------*/ |