110 lines
2.4 KiB
C++
110 lines
2.4 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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* Requires: big.cpp
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*
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*/
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#include <iostream>
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#include <fstream>
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#include <cstring>
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#include "big.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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int i;
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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("common.dss"); /* construct file I/O streams */
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ifstream public_key("public.dss");
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ifstream message;
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ifstream signature;
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Big p,q,g,y,v,u1,u2,r,s,h;
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char ifname[13],ofname[13];
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int bits;
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miracl *mip=&precision;
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/* get public data */
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common >> bits;
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mip->IOBASE=16;
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common >> p >> q >> g;
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mip->IOBASE=10;
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/* get public key of signer */
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public_key >> y;
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/* get message */
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cout << "signed file = " ;
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cin.sync();
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cin.getline(ifname,13);
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strcpy(ofname,ifname);
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strip(ofname);
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strcat(ofname,".dss");
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message.open(ifname,ios::binary|ios::in);
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if (!message)
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{ /* no message */
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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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signature.open(ofname,ios::in);
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if (!signature)
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{ /* no signature */
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cout << "signature file " << ofname << " does not exist\n";
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return 0;
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}
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signature >> r >> s;
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if (r>=q || s>=q)
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{
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cout << "Signature is NOT verified\n";
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return 0;
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}
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s=inverse(s,q);
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u1=(h*s)%q;
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u2=(r*s)%q;
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v=pow(g,u1,y,u2,p); /* v=g^u1.y^u2 mod p */
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v%=q;
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if (v==r) cout << "Signature is verified\n";
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else cout << "Signature is NOT verified\n";
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return 0;
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}
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