1 #include "os.h"
2 #include <mp.h>
3 #include <libsec.h>
4
5 int
dsaverify(DSApub * pub,DSAsig * sig,mpint * m)6 dsaverify(DSApub *pub, DSAsig *sig, mpint *m)
7 {
8 int rv = -1;
9 mpint *u1, *u2, *v, *sinv;
10
11 if(mpcmp(sig->r, mpone) < 0 || mpcmp(sig->r, pub->q) >= 0)
12 return rv;
13 if(mpcmp(sig->s, mpone) < 0 || mpcmp(sig->s, pub->q) >= 0)
14 return rv;
15 u1 = mpnew(0);
16 u2 = mpnew(0);
17 v = mpnew(0);
18 sinv = mpnew(0);
19
20 /* find (s**-1) mod q, make sure it exists */
21 mpextendedgcd(sig->s, pub->q, u1, sinv, v);
22 if(mpcmp(u1, mpone) != 0)
23 goto out;
24
25 /* u1 = (sinv * m) mod q, u2 = (r * sinv) mod q */
26 mpmul(sinv, m, u1);
27 mpmod(u1, pub->q, u1);
28 mpmul(sig->r, sinv, u2);
29 mpmod(u2, pub->q, u2);
30
31 /* v = (((alpha**u1)*(key**u2)) mod p) mod q */
32 mpexp(pub->alpha, u1, pub->p, sinv);
33 mpexp(pub->key, u2, pub->p, v);
34 mpmul(sinv, v, v);
35 mpmod(v, pub->p, v);
36 mpmod(v, pub->q, v);
37
38 if(mpcmp(v, sig->r) == 0)
39 rv = 0;
40 out:
41 mpfree(v);
42 mpfree(u1);
43 mpfree(u2);
44 mpfree(sinv);
45 return rv;
46 }
47