3 * $Id: dsa-verify.c,v 1.3 1999/12/10 23:18:38 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 1.3 1999/12/10 23:18:38 mdw
34 * Change interface for suggested destinations.
36 * Revision 1.2 1999/11/23 00:20:04 mdw
37 * Remove stray debugging code.
39 * Revision 1.1 1999/11/19 19:28:00 mdw
40 * Implementation of the Digital Signature Algorithm.
44 /*----- Header files ------------------------------------------------------*/
50 /*----- Main code ---------------------------------------------------------*/
52 /* --- @dsa_vrfy@ --- *
54 * Arguments: @const dsa_param *dp@ = pointer to DSA parameters
55 * @mp *y@ = public verification key
56 * @mp *m@ = message which was signed
57 * @mp *r, *s@ = the signature
59 * Returns: Zero if the signature is a forgery, nonzero if it's valid.
61 * Use: Verifies a DSA digital signature.
64 int dsa_vrfy(const dsa_param
*dp
, mp
*y
, mp
*m
, mp
*r
, mp
*s
)
71 /* --- Ensure that all of the signature bits are in range --- */
73 if ((r
->f
| s
->f
) & MP_NEG
)
75 if (MP_CMP(r
, >=, dp
->q
) || MP_CMP(s
, >=, dp
->q
))
78 /* --- Set up Montgomery contexts --- */
80 mpmont_create(&pm
, dp
->p
);
81 mpmont_create(&qm
, dp
->q
);
83 /* --- Compute %$w = s^{-1} \bmod q$% --- */
87 mp_gcd(0, 0, &z
, dp
->q
, s
);
88 w
= mpmont_mul(&qm
, MP_NEW
, z
, qm
.r2
);
92 /* --- Compute %$wr%$ and %$wm$% --- */
94 f
[0].exp
= mpmont_mul(&qm
, MP_NEW
, w
, m
);
95 f
[1].exp
= mpmont_mul(&qm
, MP_NEW
, w
, r
);
99 /* --- Do the exponentiation and take residue mod @q@ --- */
103 w
= mpmont_mexp(&pm
, MP_NEW
, f
, 2);
104 mp_div(0, &w
, w
, dp
->q
);
105 ok
= MP_CMP(w
, ==, r
);
107 /* --- Tidy up --- */
116 /* --- @dsa_verify@ --- *
118 * Arguments: @const dsa_param *dp@ = pointer to DSA parameters
119 * @mp *y@ = public verification key
120 * @const void *m@ = pointer to message block
121 * @size_t msz@ = size of message block
122 * @const void *r@ = pointer to @r@ signature half
123 * @size_t rsz@ = size of @r@
124 * @const void *s@ = pointer to @s@ signature half
125 * @size_t ssz@ = size of @s@
127 * Returns: Zero if the signature is a forgery, nonzero if it's valid.
129 * Use: Verifies a DSA digital signature.
132 int dsa_verify(const dsa_param
*dp
, mp
*y
,
133 const void *m
, size_t msz
,
134 const void *r
, size_t rsz
,
135 const void *s
, size_t ssz
)
137 mp
*mm
= mp_loadb(MP_NEW
, m
, msz
);
138 mp
*rm
= mp_loadb(MP_NEW
, r
, rsz
);
139 mp
*sm
= mp_loadb(MP_NEW
, s
, ssz
);
140 int ok
= dsa_vrfy(dp
, y
, mm
, rm
, sm
);
147 /*----- Test rig ----------------------------------------------------------*/
151 #include <mLib/testrig.h>
155 static int verify(int good
, dstr
*v
)
160 octet hash
[SHA_HASHSZ
];
164 dp
.q
= *(mp
**)v
[0].buf
;
165 dp
.p
= *(mp
**)v
[1].buf
;
166 dp
.g
= *(mp
**)v
[2].buf
;
167 y
= *(mp
**)v
[3].buf
;
170 sha_hash(&c
, v
[4].buf
, v
[4].len
);
173 rc
= dsa_verify(&dp
, y
, hash
, sizeof(hash
),
174 v
[5].buf
, v
[5].len
, v
[6].buf
, v
[6].len
);
178 fputs("\n*** verification failed", stderr
);
180 fputs("\n*** verification succeeded", stderr
);
181 fputs("\nq = ", stderr
); mp_writefile(dp
.q
, stderr
, 16);
182 fputs("\np = ", stderr
); mp_writefile(dp
.p
, stderr
, 16);
183 fputs("\ng = ", stderr
); mp_writefile(dp
.g
, stderr
, 16);
184 fputs("\ny = ", stderr
); mp_writefile(y
, stderr
, 16);
185 fprintf(stderr
, "\nmessage = `%s'", v
[4].buf
);
186 fputs("\nr = ", stderr
); type_hex
.dump(&v
[5], stderr
);
187 fputs("\ns = ", stderr
); type_hex
.dump(&v
[6], stderr
);
196 assert(mparena_count(MPARENA_GLOBAL
) == 0);
200 static int vgood(dstr
*v
) { return verify(1, v
); }
201 static int vbad(dstr
*v
) { return verify(0, v
); }
203 static test_chunk tests
[] = {
204 { "verify-good", vgood
,
205 { &type_mp
, &type_mp
, &type_mp
, &type_mp
,
206 &type_string
, &type_hex
, &type_hex
, 0 } },
207 { "verify-bad", vbad
,
208 { &type_mp
, &type_mp
, &type_mp
, &type_mp
,
209 &type_string
, &type_hex
, &type_hex
, 0 } },
213 int main(int argc
, char *argv
[])
216 test_run(argc
, argv
, tests
, SRCDIR
"/tests/dsa");
222 /*----- That's all, folks -------------------------------------------------*/