How to encrypt text using ElGamal encryption - encryption

Question

I just want to know how to encrypt text documents using ElGamal algorithm? I got encryption of integers using this algorithm. Please help with example

Answer 1

Here's an example using Crypto++. The answer was provided for ElGamal encryption example?.
Do you know what language or library you plan on using?
#include <iostream>
using std::cout;
using std::cerr;
using std::endl;
#include <cryptopp/osrng.h>
using CryptoPP::AutoSeededRandomPool;
#include <cryptopp/secblock.h>
using CryptoPP::SecByteBlock;
#include <cryptopp/elgamal.h>
using CryptoPP::ElGamal;
using CryptoPP::ElGamalKeys;
#include <cryptopp/cryptlib.h>
using CryptoPP::DecodingResult;
int main(int argc, char* argv[])
{
////////////////////////////////////////////////
// Generate keys
AutoSeededRandomPool rng;
cout << "Generating private key. This may take some time..." << endl;
ElGamal::Decryptor decryptor;
decryptor.AccessKey().GenerateRandomWithKeySize(rng, 512);
const ElGamalKeys::PrivateKey& privateKey = decryptor.AccessKey();
ElGamal::Encryptor encryptor(decryptor);
const PublicKey& publicKey = encryptor.AccessKey();
////////////////////////////////////////////////
// Secret to protect
static const int SECRET_SIZE = 16;
SecByteBlock plaintext( SECRET_SIZE );
memset( plaintext, 'A', SECRET_SIZE );
////////////////////////////////////////////////
// Encrypt
// Now that there is a concrete object, we can validate
assert( 0 != encryptor.FixedMaxPlaintextLength() );
assert( plaintext.size() <= encryptor.FixedMaxPlaintextLength() );
// Create cipher text space
size_t ecl = encryptor.CiphertextLength( plaintext.size() );
assert( 0 != ecl );
SecByteBlock ciphertext( ecl );
encryptor.Encrypt( rng, plaintext, plaintext.size(), ciphertext );
////////////////////////////////////////////////
// Decrypt
// Now that there is a concrete object, we can check sizes
assert( 0 != decryptor.FixedCiphertextLength() );
assert( ciphertext.size() <= decryptor.FixedCiphertextLength() );
// Create recovered text space
size_t dpl = decryptor.MaxPlaintextLength( ciphertext.size() );
assert( 0 != dpl );
SecByteBlock recovered( dpl );
DecodingResult result = decryptor.Decrypt( rng, ciphertext, ciphertext.size(), recovered );
// More sanity checks
assert( result.isValidCoding );
assert( result.messageLength <= decryptor.MaxPlaintextLength( ciphertext.size() ) );
// At this point, we can set the size of the recovered
// data. Until decryption occurs (successfully), we
// only know its maximum size
recovered.resize( result.messageLength );
// SecByteBlock is overloaded for proper results below
assert( plaintext == recovered );
// If the assert fires, we won't get this far.
if(plaintext == recovered)
cout << "Recovered plain text" << endl;
else
cout << "Failed to recover plain text" << endl;
return !(plaintext == recovered);
}