162 lines
3.7 KiB
C
162 lines
3.7 KiB
C
/*
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* Proposed Digital Signature Standard (DSS)
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*
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* Elliptic Curve Variation GF(2^m) - See Dr. Dobbs Journal April 1997
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*
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* This program verifies the signature given to a <file> in
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* <file>.ecs generated by program ecsign2
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*
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* The curve is y^2+xy = x^3+Ax^2+B over GF(2^m) using a trinomial or
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* pentanomial basis (t^m+t^a+1 or t^m+t^a+t^b+t^c+1), These parameters
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* can be generated using the findbase.cpp example program, or taken from tables
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* provided, for example in IEEE-P1363 Annex A
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*
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* The file common2.ecs is presumed to exist and contain
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* {m,A,B,q,x,y,a,b,c} where A and B are parameters of the equation
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* above, (x,y) is an initial point on the curve, {m,a,b,c} are the field
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* parameters, (b is zero for a trinomial) and q is the order of the
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* (x,y) point, itself a large prime. The number of points on the curve is
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* cf.q where cf is the "co-factor", normally 2 or 4.
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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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#ifdef MR_COUNT_OPS
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int fpm2;
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int fpi2;
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int fpc;
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int fpa;
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int fpx;
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#endif
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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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int ep,m,a,b,c;
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miracl *mip;
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epoint *g,*public;
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char ifname[50],ofname[50];
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big a2,a6,q,x,y,v,u1,u2,r,s,hash;
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/* get public data */
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fp=fopen("common2.ecs","rt");
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if (fp==NULL)
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{
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printf("file common2.ecs does not exist\n");
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return 0;
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}
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fscanf(fp,"%d\n",&m);
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mip=mirsys(MR_ROUNDUP(abs(m),4),16);
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a2=mirvar(0);
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a6=mirvar(0);
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q=mirvar(0);
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x=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(a2,fp);
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innum(a6,fp);
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innum(q,fp);
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innum(x,fp);
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innum(y,fp);
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fscanf(fp,"%d\n",&a);
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fscanf(fp,"%d\n",&b);
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fscanf(fp,"%d\n",&c);
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fclose(fp);
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ecurve2_init(m,a,b,c,a2,a6,FALSE,MR_BEST); /* initialise curve */
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g=epoint_init();
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epoint2_set(x,y,0,g); /* initialise point of order q */
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/* get public key of signer */
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fp=fopen("public.ecs","rt");
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if (fp==NULL)
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{
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printf("file public.ecs does not exist\n");
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return 0;
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}
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fscanf(fp,"%d",&ep);
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innum(x,fp);
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fclose(fp);
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public=epoint_init();
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epoint2_set(x,x,ep,public); /* decompress */
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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,".ecs");
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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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#ifdef MR_COUNT_OPS
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fpm2=fpi2=0;
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#endif
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ecurve2_mult2(u2,public,u1,g,g);
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#ifdef MR_COUNT_OPS
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printf("Number of modmuls= %d, inverses= %d\n",fpm2,fpi2);
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#endif
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epoint2_get(g,v,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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