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1 | /* -*-c-*- |
2 | * |
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3 | * $Id: dsa-verify.c,v 1.4 2000/06/17 10:53:35 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 1.4 2000/06/17 10:53:35 mdw |
34 | * Typesetting fixes. |
35 | * |
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36 | * Revision 1.3 1999/12/10 23:18:38 mdw |
37 | * Change interface for suggested destinations. |
38 | * |
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39 | * Revision 1.2 1999/11/23 00:20:04 mdw |
40 | * Remove stray debugging code. |
41 | * |
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42 | * Revision 1.1 1999/11/19 19:28:00 mdw |
43 | * Implementation of the Digital Signature Algorithm. |
44 | * |
45 | */ |
46 | |
47 | /*----- Header files ------------------------------------------------------*/ |
48 | |
49 | #include "dsa.h" |
50 | #include "mp.h" |
51 | #include "mpmont.h" |
52 | |
53 | /*----- Main code ---------------------------------------------------------*/ |
54 | |
55 | /* --- @dsa_vrfy@ --- * |
56 | * |
57 | * Arguments: @const dsa_param *dp@ = pointer to DSA parameters |
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58 | * @mp *y@ = public verification key |
59 | * @mp *m@ = message which was signed |
60 | * @mp *r, *s@ = the signature |
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61 | * |
62 | * Returns: Zero if the signature is a forgery, nonzero if it's valid. |
63 | * |
64 | * Use: Verifies a DSA digital signature. |
65 | */ |
66 | |
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67 | int dsa_vrfy(const dsa_param *dp, mp *y, mp *m, mp *r, mp *s) |
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68 | { |
69 | mpmont pm, qm; |
70 | mp *w; |
71 | mpmont_factor f[2]; |
72 | int ok; |
73 | |
74 | /* --- Ensure that all of the signature bits are in range --- */ |
75 | |
76 | if ((r->f | s->f) & MP_NEG) |
77 | return (0); |
78 | if (MP_CMP(r, >=, dp->q) || MP_CMP(s, >=, dp->q)) |
79 | return (0); |
80 | |
81 | /* --- Set up Montgomery contexts --- */ |
82 | |
83 | mpmont_create(&pm, dp->p); |
84 | mpmont_create(&qm, dp->q); |
85 | |
86 | /* --- Compute %$w = s^{-1} \bmod q$% --- */ |
87 | |
88 | { |
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89 | mp *z = MP_NEW; |
90 | mp_gcd(0, 0, &z, dp->q, s); |
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91 | w = mpmont_mul(&qm, MP_NEW, z, qm.r2); |
92 | mp_drop(z); |
93 | } |
94 | |
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95 | /* --- Compute %$wr$% and %$wm$% --- */ |
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96 | |
97 | f[0].exp = mpmont_mul(&qm, MP_NEW, w, m); |
98 | f[1].exp = mpmont_mul(&qm, MP_NEW, w, r); |
99 | mp_drop(w); |
100 | mpmont_destroy(&qm); |
101 | |
102 | /* --- Do the exponentiation and take residue mod @q@ --- */ |
103 | |
104 | f[0].base = dp->g; |
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105 | f[1].base = y; |
106 | w = mpmont_mexp(&pm, MP_NEW, f, 2); |
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107 | mp_div(0, &w, w, dp->q); |
108 | ok = MP_CMP(w, ==, r); |
109 | |
110 | /* --- Tidy up --- */ |
111 | |
112 | mp_drop(w); |
113 | mp_drop(f[0].exp); |
114 | mp_drop(f[1].exp); |
115 | mpmont_destroy(&pm); |
116 | return (ok); |
117 | } |
118 | |
119 | /* --- @dsa_verify@ --- * |
120 | * |
121 | * Arguments: @const dsa_param *dp@ = pointer to DSA parameters |
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122 | * @mp *y@ = public verification key |
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123 | * @const void *m@ = pointer to message block |
124 | * @size_t msz@ = size of message block |
125 | * @const void *r@ = pointer to @r@ signature half |
126 | * @size_t rsz@ = size of @r@ |
127 | * @const void *s@ = pointer to @s@ signature half |
128 | * @size_t ssz@ = size of @s@ |
129 | * |
130 | * Returns: Zero if the signature is a forgery, nonzero if it's valid. |
131 | * |
132 | * Use: Verifies a DSA digital signature. |
133 | */ |
134 | |
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135 | int dsa_verify(const dsa_param *dp, mp *y, |
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136 | const void *m, size_t msz, |
137 | const void *r, size_t rsz, |
138 | const void *s, size_t ssz) |
139 | { |
140 | mp *mm = mp_loadb(MP_NEW, m, msz); |
141 | mp *rm = mp_loadb(MP_NEW, r, rsz); |
142 | mp *sm = mp_loadb(MP_NEW, s, ssz); |
143 | int ok = dsa_vrfy(dp, y, mm, rm, sm); |
144 | mp_drop(mm); |
145 | mp_drop(rm); |
146 | mp_drop(sm); |
147 | return (ok); |
148 | } |
149 | |
150 | /*----- Test rig ----------------------------------------------------------*/ |
151 | |
152 | #ifdef TEST_RIG |
153 | |
154 | #include <mLib/testrig.h> |
155 | |
156 | #include "sha.h" |
157 | |
158 | static int verify(int good, dstr *v) |
159 | { |
160 | dsa_param dp; |
161 | mp *y; |
162 | sha_ctx c; |
163 | octet hash[SHA_HASHSZ]; |
164 | int ok = 1; |
165 | int rc; |
166 | |
167 | dp.q = *(mp **)v[0].buf; |
168 | dp.p = *(mp **)v[1].buf; |
169 | dp.g = *(mp **)v[2].buf; |
170 | y = *(mp **)v[3].buf; |
171 | |
172 | sha_init(&c); |
173 | sha_hash(&c, v[4].buf, v[4].len); |
174 | sha_done(&c, hash); |
175 | |
176 | rc = dsa_verify(&dp, y, hash, sizeof(hash), |
177 | v[5].buf, v[5].len, v[6].buf, v[6].len); |
178 | |
179 | if (!rc != !good) { |
180 | if (good) |
181 | fputs("\n*** verification failed", stderr); |
182 | else |
183 | fputs("\n*** verification succeeded", stderr); |
184 | fputs("\nq = ", stderr); mp_writefile(dp.q, stderr, 16); |
185 | fputs("\np = ", stderr); mp_writefile(dp.p, stderr, 16); |
186 | fputs("\ng = ", stderr); mp_writefile(dp.g, stderr, 16); |
187 | fputs("\ny = ", stderr); mp_writefile(y, stderr, 16); |
188 | fprintf(stderr, "\nmessage = `%s'", v[4].buf); |
189 | fputs("\nr = ", stderr); type_hex.dump(&v[5], stderr); |
190 | fputs("\ns = ", stderr); type_hex.dump(&v[6], stderr); |
191 | fputc('\n', stderr); |
192 | ok = 0; |
193 | } |
194 | |
195 | mp_drop(dp.p); |
196 | mp_drop(dp.q); |
197 | mp_drop(dp.g); |
198 | mp_drop(y); |
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199 | assert(mparena_count(MPARENA_GLOBAL) == 0); |
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200 | return (ok); |
201 | } |
202 | |
203 | static int vgood(dstr *v) { return verify(1, v); } |
204 | static int vbad(dstr *v) { return verify(0, v); } |
205 | |
206 | static test_chunk tests[] = { |
207 | { "verify-good", vgood, |
208 | { &type_mp, &type_mp, &type_mp, &type_mp, |
209 | &type_string, &type_hex, &type_hex, 0 } }, |
210 | { "verify-bad", vbad, |
211 | { &type_mp, &type_mp, &type_mp, &type_mp, |
212 | &type_string, &type_hex, &type_hex, 0 } }, |
213 | { 0, 0, { 0 } } |
214 | }; |
215 | |
216 | int main(int argc, char *argv[]) |
217 | { |
218 | sub_init(); |
219 | test_run(argc, argv, tests, SRCDIR "/tests/dsa"); |
220 | return (0); |
221 | } |
222 | |
223 | #endif |
224 | |
225 | /*----- That's all, folks -------------------------------------------------*/ |