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Implementing RSA Cryptography in C++

compuknow asked:

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I am trying to implement RSA using a C++ class.
Below is the class :


class rsacrypto
{
    long publickey;
    long privatekey;
    long modl; //Modulus





    public :

    rsacrypto(); //To be used to just generate private and public keys.
    rsacrypto(long &,long &,long &);//To be used just to generate private and public keys.
    rsacrypto(long key,long modulus) // Should be used when a data is to be encrypted or decrypted using a key.
    {
        publickey = privatekey = key;
        modl = modulus;
    }


    long ret_publickey()
    {
        return publickey;
    }
    long ret_privatekey()
    {
        return privatekey;
    }
    long ret_modulus()
    {
        return modl;
    }

    void encrypt(char *);
    void decrypt(char *);

};

rsacrypto::rsacrypto()
    {
        long p1,p2; //Prime numbers
        long n = 0; //Modulus
        long phi =0; //Totient value.

        long e = 0; //Public key exponent.
        long d = 0; //Private key exponent.

        p1 = genrndprimes(100,900);
        Sleep(1000);
        p1 = genrndprimes(100,900);

        n = p1*p2;
        phi = totient(n);

        e = genrndnum(2,(phi-1));

        while(gcd(e,phi)!=1)
        {
            e = genrndnum(2,(phi-1));
        }

        d = (1/e)%phi; //Modular Multiplicative Inverse.

        privatekey = e;
        publickey = d;
        modl = n;


    }


rsacrypto::rsacrypto(long &pubkey,long &privkey,long &mdls)
    {
        long p1,p2; //Prime numbers
        long n = 0; //Modulus
        long phi =0; //Totient value.

        long e = 0; //Public key exponent.
        long d = 0; //Private key exponent.

        p1 = genrndprimes(100,900);
        Sleep(1000);
        p1 = genrndprimes(100,900);

        n = p1*p2;
        phi = totient(n);

        e = genrndnum(2,(phi-1));

        while(gcd(e,phi)!=1)
        {
            e = genrndnum(2,(phi-1));
        }

        d = (1/e)%phi; //Modular Multiplicative Inverse.

        privatekey = e;
        publickey = d;

        pubkey = publickey;
        privkey = privatekey;
        mdls = n;
        modl = n;

    }


void rsacrypto::encrypt(char *dat)
{
    long siz = strlen(dat);
    for(long i=0;i<siz;i++)
    {
        dat[i]=(long)pow(dat[i],publickey)%modl;
    }
}

void rsacrypto::decrypt(char *datn)
{
    long sizz = strlen(datn);
    for(long i=0;i<sizz;i++)
    {
        datn[i]=(long)pow(datn[i],privatekey)%modl;
    }

}



genrndprimes(a,b) : Generates a random prime number between a and b (also inclusive of a and b if any or both a and b are prime).
genrndnum(a,b) : Generates a random number between a and b (also inclusive of a and b).


Main Program :


void main()
{
	char datm[]="Hello!! , Implementing RSA";
	
	rsacrypto m;
	long prkey = m.ret_privatekey();
	long publkey = m.ret_publickey();
	long modulm = m.ret_modulus();
	
	rsacrypto jj(publkey,modulm);
	rsacrypto ll(prkey,modulm);
	
	jj.encrypt(datm);
	
	puts(datm);
	
	cout<<"\n";
	
	ll.decrypt(datm);
	
	puts(datm);
	
	
}



The problem i face is this output :

Upon Encryption : 25 face characters (ASCII value value Unknown).
Upon Decryption : (SAME) 25 face characters (ASCII value Unknown).
Tags: C++, cryptography

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