www.pudn.com > miracl.zip > CRENCODE.CPP

/* 
 *   Cramer-Shoup Public Key Encryption - Hybrid Implementation  
 * 
 *   This program encrypts a file fred.xxx to fred.crs. The AES encryption 
 *   key is encrypted under the public key in the file fred.key 
 * 
 *   The public key comes from from public.crs 
 * 
 *   Requires: big.cpp 
 * 
 *   Copyright (c) 1999 Shamus Software Ltd. 
 */ 
 
#include  
#include  
#include  
#include  
 
using namespace std; 
 
Miracl precision(300,256); 
 
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; 
    } 
} 
 
void hash(sha *s,Big x) 
{ /* hash in a big number one byte at a time */ 
    sha sh; 
    int ch; 
    while (x!=0) 
    { 
        ch=x%256; x/=256; 
        shs_process(s,ch); 
    } 
} 
 
int main() 
{ 
    int i,bits; 
    ifstream common("common.crs");    // construct file I/O streams  
    ifstream plaintext,public_key("public.crs"); 
    ofstream key_file,ciphertext; 
    Big p,q,g1,g2,h,m,r,u1,u2,e,v,ex,c,d,alpha; 
    static char ifname[100],ofname[100]; 
    char ch,H[20],iv[16],block[16];  
    sha sh; 
    aes a; 
    long seed; 
    miracl *mip=&precision; 
 
// randomise  
    cout << "Enter 9 digit random number seed  = "; 
    cin >> seed; 
    irand(seed); 
    mip->IOBASE=16; 
 
// get common data  
    common >> bits; 
    common >> q >> p >> g1 >> g2; 
 
// get public key of receiver  
    public_key >> c >> d >> h; 
 
    r=rand(q); 
 
    shs_init(&sh); 
    hash(&sh,pow(h,r,p));                           
    shs_hash(&sh,H);      // AES Key = Hash(h^r mod p) 
    for (i=0;i<16;i++) iv[i]=i;  // Set CFB IV 
    aes_init(&a,MR_PCFB1,16,H,iv);        // Set 128 bit AES Key 
 
// figure out where input is coming from 
 
    cout << "file to be encoded = " ; 
    cin >> ifname; 
 
   /* set up output files */ 
    strcpy(ofname,ifname); 
    strip(ofname); 
    strcat(ofname,".crs"); 
    plaintext.open(ifname,ios::in);  
    if (!plaintext) 
    { 
        cout << "Unable to open file " << ifname << "\n"; 
        return 0; 
    } 
    cout << "encoding message\n"; 
 
    ciphertext.open(ofname,ios::binary|ios::out); 
 
    u1=pow(g1,r,p); 
    u2=pow(g2,r,p); 
 
    shs_init(&sh); 
    hash(&sh,u1); 
    hash(&sh,u2); 
 
// now encrypt the plaintext  
// and hash in the ciphertext. 
 
    forever 
    { // encrypt input .. 
        plaintext.get(ch); 
        if (plaintext.eof()) break; 
        aes_encrypt(&a,&ch); 
        shs_process(&sh,ch); 
        ciphertext << ch; 
    } 
 
    aes_end(&a); 
 
    shs_hash(&sh,H); 
    mip->INPLEN=20;  
    mip->IOBASE=256; 
    alpha=(char *)H;   // alpha=Hash(u1,u2,ciphertext) 
 
    ex=(r*alpha)%q; 
    v=pow(c,r,d,ex,p);      // multi-exponentiation 
 
    strip(ofname); 
    strcat(ofname,".key"); 
    mip->IOBASE=16; 
    key_file.open(ofname); 
    key_file << u1 << endl; 
    key_file << u2 << endl; 
    key_file << v << endl; 
    return 0; 
}