171 lines
3.7 KiB
C
171 lines
3.7 KiB
C
/*
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* Elliptic Curve Digital Signature Algorithm (ECDSA)
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*
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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 ecsign
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*
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* The curve is y^2=x^3+Ax+B mod p
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*
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* The file common.ecs is presumed to exist, and to contain the domain
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* information {p,A,B,q,x,y}, where A and B are curve parameters, (x,y) are
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* a point of order q, p is the prime modulus, and q is the order of the
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* point (x,y). In fact normally q is the prime number of points counted
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* on the curve.
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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,fpi2,fpc,fpa,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 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 bits,ep;
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epoint *g,*publc;
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char ifname[50],ofname[50];
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big a,b,p,q,x,y,v,u1,u2,r,s,hash;
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miracl *mip;
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/* get public data */
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#ifndef MR_EDWARDS
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fp=fopen("common.ecs","rt");
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if (fp==NULL)
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{
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printf("file common.ecs 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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#else
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fp=fopen("edwards.ecs","rt");
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if (fp==NULL)
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{
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printf("file edwards.ecs 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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#endif
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mip=mirsys(bits/4,16); /* Use Hex Internally */
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a=mirvar(0);
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b=mirvar(0);
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p=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(p,fp);
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innum(a,fp);
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innum(b,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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fclose(fp);
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ecurve_init(a,b,p,MR_PROJECTIVE); /* initialise curve */
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g=epoint_init();
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epoint_set(x,y,0,g);
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if (!epoint_set(x,y,0,g)) /* initialise point of order q */
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{
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printf("1. Problem - point (x,y) is not on the curve\n");
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exit(0);
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}
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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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publc=epoint_init();
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if (!epoint_set(x,x,ep,publc)) /* decompress */
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{
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printf("1. Not a point on the curve\n");
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return 0;
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}
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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=fpc=fpa=fpx=0;
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#endif
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ecurve_mult2(u2,publc,u1,g,g);
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#ifdef MR_COUNT_OPS
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printf("Number of modmuls= %d, inverses= %d\n",fpc,fpx);
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#endif
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epoint_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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