121 lines
2.6 KiB
C
121 lines
2.6 KiB
C
/*
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* Digital Signature Algorithm (DSA)
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*
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* See Communications ACM July 1992, Vol. 35 No. 7
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* This new standard for digital signatures has been proposed by
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* the American National Institute of Standards and Technology (NIST)
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* under advisement from the National Security Agency (NSA).
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*
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* This program verifies a the signature given to a <file> in
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* <file>.dss generated by program dssign.c
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*
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*/
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#include <stdio.h>
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#include "miracl.h"
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#include <stdlib.h>
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#include <string.h>
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void strip(char *name)
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{ /* strip off filename extension */
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int i;
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for (i=0;name[i]!='\0';i++)
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{
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if (name[i]!='.') continue;
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name[i]='\0';
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break;
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}
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}
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static void hashing(FILE *fp,big hash)
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{ /* compute hash function */
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char h[20];
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sha sh;
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int i,ch;
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shs_init(&sh);
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while ((ch=fgetc(fp))!=EOF) shs_process(&sh,ch);
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shs_hash(&sh,h);
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bytes_to_big(20,h,hash);
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}
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int main()
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{
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FILE *fp;
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char ifname[50],ofname[50];
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big p,q,g,y,v,u1,u2,r,s,hash;
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int bits;
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miracl *mip;
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/* get public data */
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fp=fopen("common.dss","rt");
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if (fp==NULL)
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{
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printf("file common.dss does not exist\n");
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return 0;
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}
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fscanf(fp,"%d\n",&bits);
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mip=mirsys(bits/4,16); /* Use Hex Internally */
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p=mirvar(0);
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q=mirvar(0);
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g=mirvar(0);
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y=mirvar(0);
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v=mirvar(0);
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u1=mirvar(0);
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u2=mirvar(0);
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s=mirvar(0);
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r=mirvar(0);
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hash=mirvar(0);
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innum(p,fp);
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innum(q,fp);
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innum(g,fp);
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fclose(fp);
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/* get public key of signer */
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fp=fopen("public.dss","rt");
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if (fp==NULL)
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{
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printf("file public.dss does not exist\n");
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return 0;
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}
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innum(y,fp);
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fclose(fp);
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/* get message */
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printf("signed file = ");
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gets(ifname);
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strcpy(ofname,ifname);
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strip(ofname);
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strcat(ofname,".dss");
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if ((fp=fopen(ifname,"rb"))==NULL)
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{ /* no message */
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printf("Unable to open file %s\n",ifname);
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return 0;
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}
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hashing(fp,hash);
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fclose(fp);
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fp=fopen(ofname,"rt");
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if (fp==NULL)
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{ /* no signature */
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printf("signature file %s does not exist\n",ofname);
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return 0;
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}
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innum(r,fp);
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innum(s,fp);
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fclose(fp);
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if (mr_compare(r,q)>=0 || mr_compare(s,q)>=0)
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{
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printf("Signature is NOT verified\n");
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return 0;
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}
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xgcd(s,q,s,s,s);
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mad(hash,s,s,q,q,u1);
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mad(r,s,s,q,q,u2);
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powmod2(g,u1,y,u2,p,v);
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divide(v,q,q);
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if (mr_compare(v,r)==0) printf("Signature is verified\n");
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else printf("Signature is NOT verified\n");
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return 0;
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}
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