3 * DSA signature verification
5 * (c) 1999 Straylight/Edgeware
8 /*----- Licensing notice --------------------------------------------------*
10 * This file is part of Catacomb.
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.
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.
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,
28 /*----- Header files ------------------------------------------------------*/
34 /*----- Main code ---------------------------------------------------------*/
36 /* --- @dsa_vrfy@ --- *
38 * Arguments: @const dsa_param *dp@ = pointer to DSA parameters
39 * @mp *y@ = public verification key
40 * @mp *m@ = message which was signed
41 * @mp *r, *s@ = the signature
43 * Returns: Zero if the signature is a forgery, nonzero if it's valid.
45 * Use: Verifies a DSA digital signature.
48 int dsa_vrfy(const dsa_param
*dp
, mp
*y
, mp
*m
, mp
*r
, mp
*s
)
55 /* --- Ensure that all of the signature bits are in range --- */
57 if ((r
->f
| s
->f
) & MP_NEG
)
59 if (MP_CMP(r
, >=, dp
->q
) || MP_CMP(s
, >=, dp
->q
))
62 /* --- Set up Montgomery contexts --- */
64 mpmont_create(&pm
, dp
->p
);
65 mpmont_create(&qm
, dp
->q
);
67 /* --- Compute %$w = s^{-1} \bmod q$% --- */
70 mp
*z
= mp_modinv(MP_NEW
, s
, dp
->q
);
71 w
= mpmont_mul(&qm
, MP_NEW
, z
, qm
.r2
);
75 /* --- Compute %$wr$% and %$wm$% --- */
77 f
[0].exp
= mpmont_mul(&qm
, MP_NEW
, w
, m
);
78 f
[1].exp
= mpmont_mul(&qm
, MP_NEW
, w
, r
);
82 /* --- Do the exponentiation and take residue mod @q@ --- */
86 w
= mpmont_mexp(&pm
, MP_NEW
, f
, 2);
87 mp_div(0, &w
, w
, dp
->q
);
99 /* --- @dsa_verify@ --- *
101 * Arguments: @const dsa_param *dp@ = pointer to DSA parameters
102 * @mp *y@ = public verification key
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@
110 * Returns: Zero if the signature is a forgery, nonzero if it's valid.
112 * Use: Verifies a DSA digital signature.
115 int dsa_verify(const dsa_param
*dp
, mp
*y
,
116 const void *m
, size_t msz
,
117 const void *r
, size_t rsz
,
118 const void *s
, size_t ssz
)
120 mp
*mm
= dsa_h2n(MP_NEW
, dp
->q
, m
, msz
);
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
);
130 /*----- Test rig ----------------------------------------------------------*/
134 #include <mLib/testrig.h>
138 static int verify(int good
, dstr
*v
)
143 octet hash
[SHA_HASHSZ
];
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
;
153 sha_hash(&c
, v
[4].buf
, v
[4].len
);
156 rc
= dsa_verify(&dp
, y
, hash
, sizeof(hash
),
157 v
[5].buf
, v
[5].len
, v
[6].buf
, v
[6].len
);
161 fputs("\n*** verification failed", stderr
);
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
);
179 assert(mparena_count(MPARENA_GLOBAL
) == 0);
183 static int vgood(dstr
*v
) { return verify(1, v
); }
184 static int vbad(dstr
*v
) { return verify(0, v
); }
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 } },
196 int main(int argc
, char *argv
[])
199 test_run(argc
, argv
, tests
, SRCDIR
"/t/dsa");
205 /*----- That's all, folks -------------------------------------------------*/