text: /*
   *   Proposed Digital Signature Standard (DSS)
   *
   *   Elliptic Curve Variation GF(2^m) - See Dr. Dobbs Journal April 1997
   *
   *   This program verifies the signature given to a <file> in
   *   <file>.ecs generated by program ecsign
   * 
   *   The curve is y^2+xy = x^3+Ax^2+B over GF(2^m) using a trinomial or 
   *   pentanomial basis (t^m+t^a+1 or t^m+t^a+t^b+t^c+1). These parameters
   *   can be generated using the findbase.cpp example program, or taken from tables
   *   provided, for example in IEEE-P1363 Annex A
   *
   *   The file common2.ecs is presumed to exist and contain 
   *   {m,A,B,q,x,y,a,b,c,q} where A and B are parameters of the equation 
   *   above, (x,y) is an initial point on the curve, {m,a,b,c} are the field 
   *   parameters, (b is zero for a trinomial) and q is the order of the 
   *   (x,y) point, itself a large prime. The number of points on the curve is 
   *   cf.q where cf is the "co-factor", normally 2 or 4.
   * 
   *   Requires: big.cpp ec2.cpp
   *
   */
  
  #include <iostream>
  #include <fstream>
  #include <cstring>
  #include "ec2.h"
  
  using namespace std;
  
  Miracl precision(200,256);
  
  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 Big Hash(ifstream &fp)
  { /* compute hash function */
      char ch,s[20];
      Big h;
      sha sh;
      shs_init(&sh);
      forever 
      { /* read in bytes from message file */
          fp.get(ch);
          if (fp.eof()) break;
          shs_process(&sh,ch);
      }
      shs_hash(&sh,s);
      h=from_binary(20,s);
      return h;
  }
  
  int main()
  {
      ifstream common("common2.ecs");    /* construct file I/O streams */
      ifstream public_key("public.ecs");
      ifstream message;
      ifstream signature;
      EC2 G,Pub;
      int ep,m,a,b,c;
      Big a2,a6,q,x,y,v,u1,u2,r,s,h;
      char ifname[50],ofname[50];
      miracl *mip=&precision;
  
  /* get public data */
  
      common >> m;
      mip->IOBASE=16;
      common >> a2 >> a6 >> q >> x >> y;
      mip->IOBASE=10;
      common >> a >> b >> c;
  
      ecurve2(m,a,b,c,a2,a6,FALSE,MR_PROJECTIVE);
      G=EC2(x,y);
  /* get public key of signer */
      public_key >> ep >> x;
      Pub=EC2(x,ep);         // decompress
  /* get message */
      cout << "signed file = " ;
      cin.sync();
      cin.getline(ifname,13);
      strcpy(ofname,ifname);
      strip(ofname);
      strcat(ofname,".ecs");
      message.open(ifname,ios::binary|ios::in); 
      if (!message)
      { /* no message */
          cout << "Unable to open file " << ifname << "\n";
          return 0;
      }
      h=Hash(message);
  
      mip->IOBASE=10;
      signature.open(ofname,ios::in);
      if (!signature)
      { /* no signature */
          cout << "signature file " << ofname << " does not exist\n";
          return 0;
      }
      signature >> r >> s;
      if (r>=q || s>=q)
      {
          cout << "Signature is NOT verified\n";
          return 0;
      }
      s=inverse(s,q);
      u1=(h*s)%q;
      u2=(r*s)%q;
  
      G=mul(u2,Pub,u1,G);
      G.get(v);
      v%=q;
      if (v==r) cout << "Signature is verified\n";
      else      cout << "Signature is NOT verified\n";
      return 0;
  }
  
  