126 lines
3.1 KiB
C++
126 lines
3.1 KiB
C++
/*
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* 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 asks for the name of a <file>, computes its message digest,
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* signs it, and outputs the signature to a file <file>.ecs. It is assumed
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* that curve parameters are available from a file common.ecs, as well as
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* the private key of the signer previously generated by the ecsgen program
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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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* Requires: big.cpp ec2.cpp
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*/
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#include <iostream>
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#include <cstring>
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#include <fstream>
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#include "ec2.h"
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using namespace std;
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Miracl precision(200,256);
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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 Big Hash(ifstream &fp)
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{ /* compute hash function */
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char ch,s[20];
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Big h;
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sha sh;
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shs_init(&sh);
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forever
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{ /* read in bytes from message file */
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fp.get(ch);
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if (fp.eof()) break;
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shs_process(&sh,ch);
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}
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shs_hash(&sh,s);
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h=from_binary(20,s);
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return h;
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}
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int main()
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{
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ifstream common("common2.ecs"); /* construct file I/O streams */
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ifstream private_key("private.ecs");
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ifstream message;
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ofstream signature;
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char ifname[50],ofname[50];
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EC2 G;
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Big a2,a6,q,x,y,h,r,s,d,k;
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long seed;
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int m,a,b,c;
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miracl *mip=&precision;
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/* randomise */
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cout << "Enter 9 digit random number seed = ";
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cin >> seed;
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irand(seed);
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/* get common data */
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common >> m;
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mip->IOBASE=16;
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common >> a2 >> a6 >> q >> x >> y;
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mip->IOBASE=10;
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common >> a >> b >> c;
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/* calculate r - this can be done off-line,
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and hence amortized to almost nothing */
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ecurve2(m,a,b,c,a2,a6,FALSE,MR_PROJECTIVE);
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G=EC2(x,y);
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k=rand(q);
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G*=k; /* see ebrick2.cpp for technique to speed this up */
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G.get(r);
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r%=q;
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/* get private key of recipient */
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private_key >> d;
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/* get message */
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cout << "file to be signed = " ;
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cin >> 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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message.open(ifname,ios::binary|ios::in);
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if (!message)
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{
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cout << "Unable to open file " << ifname << "\n";
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return 0;
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}
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h=Hash(message);
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/* calculate s */
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k=inverse(k,q);
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s=((h+d*r)*k)%q;
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signature.open(ofname);
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mip->IOBASE=10;
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signature << r << endl;
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signature << s << endl;
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return 0;
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}
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