3 * $Id: dsa-verify.c,v 1.4 2000/06/17 10:53:35 mdw Exp $
5 * DSA signature verification
7 * (c) 1999 Straylight/Edgeware
10 /*----- Licensing notice --------------------------------------------------*
12 * This file is part of Catacomb.
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.
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.
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,
30 /*----- Revision history --------------------------------------------------*
32 * $Log: dsa-verify.c,v $
33 * Revision 1.4 2000/06/17 10:53:35 mdw
36 * Revision 1.3 1999/12/10 23:18:38 mdw
37 * Change interface for suggested destinations.
39 * Revision 1.2 1999/11/23 00:20:04 mdw
40 * Remove stray debugging code.
42 * Revision 1.1 1999/11/19 19:28:00 mdw
43 * Implementation of the Digital Signature Algorithm.
47 /*----- Header files ------------------------------------------------------*/
53 /*----- Main code ---------------------------------------------------------*/
55 /* --- @dsa_vrfy@ --- *
57 * Arguments: @const dsa_param *dp@ = pointer to DSA parameters
58 * @mp *y@ = public verification key
59 * @mp *m@ = message which was signed
60 * @mp *r, *s@ = the signature
62 * Returns: Zero if the signature is a forgery, nonzero if it's valid.
64 * Use: Verifies a DSA digital signature.
67 int dsa_vrfy(const dsa_param
*dp
, mp
*y
, mp
*m
, mp
*r
, mp
*s
)
74 /* --- Ensure that all of the signature bits are in range --- */
76 if ((r
->f
| s
->f
) & MP_NEG
)
78 if (MP_CMP(r
, >=, dp
->q
) || MP_CMP(s
, >=, dp
->q
))
81 /* --- Set up Montgomery contexts --- */
83 mpmont_create(&pm
, dp
->p
);
84 mpmont_create(&qm
, dp
->q
);
86 /* --- Compute %$w = s^{-1} \bmod q$% --- */
90 mp_gcd(0, 0, &z
, dp
->q
, s
);
91 w
= mpmont_mul(&qm
, MP_NEW
, z
, qm
.r2
);
95 /* --- Compute %$wr$% and %$wm$% --- */
97 f
[0].exp
= mpmont_mul(&qm
, MP_NEW
, w
, m
);
98 f
[1].exp
= mpmont_mul(&qm
, MP_NEW
, w
, r
);
102 /* --- Do the exponentiation and take residue mod @q@ --- */
106 w
= mpmont_mexp(&pm
, MP_NEW
, f
, 2);
107 mp_div(0, &w
, w
, dp
->q
);
108 ok
= MP_CMP(w
, ==, r
);
110 /* --- Tidy up --- */
119 /* --- @dsa_verify@ --- *
121 * Arguments: @const dsa_param *dp@ = pointer to DSA parameters
122 * @mp *y@ = public verification key
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@
130 * Returns: Zero if the signature is a forgery, nonzero if it's valid.
132 * Use: Verifies a DSA digital signature.
135 int dsa_verify(const dsa_param
*dp
, mp
*y
,
136 const void *m
, size_t msz
,
137 const void *r
, size_t rsz
,
138 const void *s
, size_t ssz
)
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
);
150 /*----- Test rig ----------------------------------------------------------*/
154 #include <mLib/testrig.h>
158 static int verify(int good
, dstr
*v
)
163 octet hash
[SHA_HASHSZ
];
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
;
173 sha_hash(&c
, v
[4].buf
, v
[4].len
);
176 rc
= dsa_verify(&dp
, y
, hash
, sizeof(hash
),
177 v
[5].buf
, v
[5].len
, v
[6].buf
, v
[6].len
);
181 fputs("\n*** verification failed", stderr
);
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
);
199 assert(mparena_count(MPARENA_GLOBAL
) == 0);
203 static int vgood(dstr
*v
) { return verify(1, v
); }
204 static int vbad(dstr
*v
) { return verify(0, v
); }
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 } },
216 int main(int argc
, char *argv
[])
219 test_run(argc
, argv
, tests
, SRCDIR
"/tests/dsa");
225 /*----- That's all, folks -------------------------------------------------*/