124 lines
2.7 KiB
C
124 lines
2.7 KiB
C
/*
|
|
* Digital Signature Algorithm (DSA)
|
|
*
|
|
* See Communications ACM July 1992, Vol. 35 No. 7
|
|
* This new standard for digital signatures has been proposed by
|
|
* the American National Institute of Standards and Technology (NIST)
|
|
* under advisement from the National Security Agency (NSA).
|
|
*
|
|
* This program asks for the name of a <file>, computes its message digest,
|
|
* signs it, and outputs the signature to a file <file>.dss. It is assumed
|
|
* that the common values p, q and g, as well as the private key of the
|
|
* signer have been previously generated by the dssgen program
|
|
*
|
|
*/
|
|
|
|
#include <stdio.h>
|
|
#include "miracl.h"
|
|
#include <stdlib.h>
|
|
#include <string.h>
|
|
|
|
void strip(char *name)
|
|
{ /* strip off filename extension */
|
|
int i;
|
|
for (i=0;name[i]!='\0';i++)
|
|
{
|
|
if (name[i]!='.') continue;
|
|
name[i]='\0';
|
|
break;
|
|
}
|
|
}
|
|
|
|
static void hashing(FILE *fp,big hash)
|
|
{ /* compute hash function */
|
|
char h[20];
|
|
int i,ch;
|
|
sha sh;
|
|
shs_init(&sh);
|
|
while ((ch=fgetc(fp))!=EOF) shs_process(&sh,ch);
|
|
shs_hash(&sh,h);
|
|
bytes_to_big(20,h,hash);
|
|
}
|
|
|
|
int main()
|
|
{
|
|
FILE *fp;
|
|
char ifname[50],ofname[50];
|
|
big p,q,g,x,r,s,k,hash;
|
|
long seed;
|
|
int bits;
|
|
miracl *mip;
|
|
|
|
/* get public data */
|
|
fp=fopen("common.dss","rt");
|
|
if (fp==NULL)
|
|
{
|
|
printf("file common.dss does not exist\n");
|
|
return 0;
|
|
}
|
|
|
|
fscanf(fp,"%d\n",&bits);
|
|
mip=mirsys(bits/4,16); /* use Hex internally */
|
|
p=mirvar(0);
|
|
q=mirvar(0);
|
|
g=mirvar(0);
|
|
x=mirvar(0);
|
|
r=mirvar(0);
|
|
s=mirvar(0);
|
|
k=mirvar(0);
|
|
hash=mirvar(0);
|
|
|
|
innum(p,fp);
|
|
innum(q,fp);
|
|
innum(g,fp);
|
|
fclose(fp);
|
|
|
|
/* randomise */
|
|
printf("Enter 9 digit random number seed = ");
|
|
scanf("%ld",&seed);
|
|
getchar();
|
|
irand(seed);
|
|
|
|
/* calculate r - this can be done offline,
|
|
and hence amortized to almost nothing */
|
|
bigrand(q,k);
|
|
powmod(g,k,p,r); /* see brick.c for method to speed this up */
|
|
divide(r,q,q);
|
|
|
|
/* get private key of signer */
|
|
fp=fopen("private.dss","rt");
|
|
if (fp==NULL)
|
|
{
|
|
printf("file private.dss does not exist\n");
|
|
return 0;
|
|
}
|
|
innum(x,fp);
|
|
fclose(fp);
|
|
|
|
/* calculate message digest */
|
|
printf("file to be signed = ");
|
|
gets(ifname);
|
|
strcpy(ofname,ifname);
|
|
strip(ofname);
|
|
strcat(ofname,".dss");
|
|
if ((fp=fopen(ifname,"rb"))==NULL)
|
|
{
|
|
printf("Unable to open file %s\n",ifname);
|
|
return 0;
|
|
}
|
|
hashing(fp,hash);
|
|
fclose(fp);
|
|
|
|
/* calculate s */
|
|
xgcd(k,q,k,k,k);
|
|
mad(x,r,hash,q,q,s);
|
|
mad(s,k,k,q,q,s);
|
|
fp=fopen(ofname,"wt");
|
|
otnum(r,fp);
|
|
otnum(s,fp);
|
|
fclose(fp);
|
|
mirexit();
|
|
return 0;
|
|
}
|
|
|