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1 | /* -*-c-*- |
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2 | * |
3 | * DSA signature verification |
4 | * |
5 | * (c) 1999 Straylight/Edgeware |
6 | */ |
7 | |
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8 | /*----- Licensing notice --------------------------------------------------* |
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9 | * |
10 | * This file is part of Catacomb. |
11 | * |
12 | * Catacomb is free software; you can redistribute it and/or modify |
13 | * it under the terms of the GNU Library General Public License as |
14 | * published by the Free Software Foundation; either version 2 of the |
15 | * License, or (at your option) any later version. |
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16 | * |
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17 | * Catacomb is distributed in the hope that it will be useful, |
18 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
19 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
20 | * GNU Library General Public License for more details. |
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21 | * |
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22 | * You should have received a copy of the GNU Library General Public |
23 | * License along with Catacomb; if not, write to the Free |
24 | * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, |
25 | * MA 02111-1307, USA. |
26 | */ |
27 | |
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28 | /*----- Header files ------------------------------------------------------*/ |
29 | |
30 | #include "dsa.h" |
31 | #include "mp.h" |
32 | #include "mpmont.h" |
33 | |
34 | /*----- Main code ---------------------------------------------------------*/ |
35 | |
36 | /* --- @dsa_vrfy@ --- * |
37 | * |
38 | * Arguments: @const dsa_param *dp@ = pointer to DSA parameters |
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39 | * @mp *y@ = public verification key |
40 | * @mp *m@ = message which was signed |
41 | * @mp *r, *s@ = the signature |
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42 | * |
43 | * Returns: Zero if the signature is a forgery, nonzero if it's valid. |
44 | * |
45 | * Use: Verifies a DSA digital signature. |
46 | */ |
47 | |
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48 | int dsa_vrfy(const dsa_param *dp, mp *y, mp *m, mp *r, mp *s) |
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49 | { |
50 | mpmont pm, qm; |
51 | mp *w; |
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52 | mp_expfactor f[2]; |
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53 | int ok; |
54 | |
55 | /* --- Ensure that all of the signature bits are in range --- */ |
56 | |
57 | if ((r->f | s->f) & MP_NEG) |
58 | return (0); |
59 | if (MP_CMP(r, >=, dp->q) || MP_CMP(s, >=, dp->q)) |
60 | return (0); |
61 | |
62 | /* --- Set up Montgomery contexts --- */ |
63 | |
64 | mpmont_create(&pm, dp->p); |
65 | mpmont_create(&qm, dp->q); |
66 | |
67 | /* --- Compute %$w = s^{-1} \bmod q$% --- */ |
68 | |
69 | { |
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70 | mp *z = mp_modinv(MP_NEW, s, dp->q); |
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71 | w = mpmont_mul(&qm, MP_NEW, z, qm.r2); |
72 | mp_drop(z); |
73 | } |
74 | |
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75 | /* --- Compute %$wr$% and %$wm$% --- */ |
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76 | |
77 | f[0].exp = mpmont_mul(&qm, MP_NEW, w, m); |
78 | f[1].exp = mpmont_mul(&qm, MP_NEW, w, r); |
79 | mp_drop(w); |
80 | mpmont_destroy(&qm); |
81 | |
82 | /* --- Do the exponentiation and take residue mod @q@ --- */ |
83 | |
84 | f[0].base = dp->g; |
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85 | f[1].base = y; |
86 | w = mpmont_mexp(&pm, MP_NEW, f, 2); |
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87 | mp_div(0, &w, w, dp->q); |
22bab86c |
88 | ok = MP_EQ(w, r); |
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89 | |
90 | /* --- Tidy up --- */ |
91 | |
92 | mp_drop(w); |
93 | mp_drop(f[0].exp); |
94 | mp_drop(f[1].exp); |
95 | mpmont_destroy(&pm); |
96 | return (ok); |
97 | } |
98 | |
99 | /* --- @dsa_verify@ --- * |
100 | * |
101 | * Arguments: @const dsa_param *dp@ = pointer to DSA parameters |
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102 | * @mp *y@ = public verification key |
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103 | * @const void *m@ = pointer to message block |
104 | * @size_t msz@ = size of message block |
105 | * @const void *r@ = pointer to @r@ signature half |
106 | * @size_t rsz@ = size of @r@ |
107 | * @const void *s@ = pointer to @s@ signature half |
108 | * @size_t ssz@ = size of @s@ |
109 | * |
110 | * Returns: Zero if the signature is a forgery, nonzero if it's valid. |
111 | * |
112 | * Use: Verifies a DSA digital signature. |
113 | */ |
114 | |
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115 | int dsa_verify(const dsa_param *dp, mp *y, |
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116 | const void *m, size_t msz, |
117 | const void *r, size_t rsz, |
118 | const void *s, size_t ssz) |
119 | { |
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120 | mp *mm = dsa_h2n(MP_NEW, dp->q, m, msz); |
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121 | mp *rm = mp_loadb(MP_NEW, r, rsz); |
122 | mp *sm = mp_loadb(MP_NEW, s, ssz); |
123 | int ok = dsa_vrfy(dp, y, mm, rm, sm); |
124 | mp_drop(mm); |
125 | mp_drop(rm); |
126 | mp_drop(sm); |
127 | return (ok); |
128 | } |
129 | |
130 | /*----- Test rig ----------------------------------------------------------*/ |
131 | |
132 | #ifdef TEST_RIG |
133 | |
134 | #include <mLib/testrig.h> |
135 | |
136 | #include "sha.h" |
137 | |
138 | static int verify(int good, dstr *v) |
139 | { |
140 | dsa_param dp; |
141 | mp *y; |
142 | sha_ctx c; |
143 | octet hash[SHA_HASHSZ]; |
144 | int ok = 1; |
145 | int rc; |
146 | |
147 | dp.q = *(mp **)v[0].buf; |
148 | dp.p = *(mp **)v[1].buf; |
149 | dp.g = *(mp **)v[2].buf; |
150 | y = *(mp **)v[3].buf; |
151 | |
152 | sha_init(&c); |
153 | sha_hash(&c, v[4].buf, v[4].len); |
154 | sha_done(&c, hash); |
155 | |
156 | rc = dsa_verify(&dp, y, hash, sizeof(hash), |
157 | v[5].buf, v[5].len, v[6].buf, v[6].len); |
158 | |
159 | if (!rc != !good) { |
160 | if (good) |
161 | fputs("\n*** verification failed", stderr); |
162 | else |
163 | fputs("\n*** verification succeeded", stderr); |
164 | fputs("\nq = ", stderr); mp_writefile(dp.q, stderr, 16); |
165 | fputs("\np = ", stderr); mp_writefile(dp.p, stderr, 16); |
166 | fputs("\ng = ", stderr); mp_writefile(dp.g, stderr, 16); |
167 | fputs("\ny = ", stderr); mp_writefile(y, stderr, 16); |
168 | fprintf(stderr, "\nmessage = `%s'", v[4].buf); |
169 | fputs("\nr = ", stderr); type_hex.dump(&v[5], stderr); |
170 | fputs("\ns = ", stderr); type_hex.dump(&v[6], stderr); |
171 | fputc('\n', stderr); |
172 | ok = 0; |
173 | } |
174 | |
175 | mp_drop(dp.p); |
176 | mp_drop(dp.q); |
177 | mp_drop(dp.g); |
178 | mp_drop(y); |
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179 | assert(mparena_count(MPARENA_GLOBAL) == 0); |
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180 | return (ok); |
181 | } |
182 | |
183 | static int vgood(dstr *v) { return verify(1, v); } |
184 | static int vbad(dstr *v) { return verify(0, v); } |
185 | |
186 | static test_chunk tests[] = { |
187 | { "verify-good", vgood, |
188 | { &type_mp, &type_mp, &type_mp, &type_mp, |
189 | &type_string, &type_hex, &type_hex, 0 } }, |
190 | { "verify-bad", vbad, |
191 | { &type_mp, &type_mp, &type_mp, &type_mp, |
192 | &type_string, &type_hex, &type_hex, 0 } }, |
193 | { 0, 0, { 0 } } |
194 | }; |
195 | |
196 | int main(int argc, char *argv[]) |
197 | { |
198 | sub_init(); |
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199 | test_run(argc, argv, tests, SRCDIR "/t/dsa"); |
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200 | return (0); |
201 | } |
202 | |
203 | #endif |
204 | |
205 | /*----- That's all, folks -------------------------------------------------*/ |