How to loop over Blowfish Crypto++

Question

I am running Crypto++ doing speed tests on encryption algorithms. I am trying to time how long it takes to encrypt, then decrypt the data(eventually with more file sizes and dif

Answer 1

At each iteration of the loop, you have to call:

• cipher.clear()
• recovered.clear()

Otherwise, the StringSink's just keep adding to the end of a previous value. You will fail on the 2nd and subsequent iterations of your loop (the 1st should be OK).

Also, there is no Resynchronize, so you can't call e.Resynchronize(iv) to restart a cipher. You have to call e.SetKeyWithIV(key, key.size(), iv) at each iteration of your loop.

Below, I could not duplicate your reuse problem. The encryption object was reused, while the decryption object was created new for each iteration. The result of running the program:

$ ./cryptopp-test.exe
plain text: String 1
recovered text: String 1
plain text: String 2
recovered text: String 2
plain text: String 3
recovered text: String 3
plain text: String 4
recovered text: String 4
plain text: String 5
recovered text: String 5

---

AutoSeededRandomPool prng;

SecByteBlock key(Blowfish::DEFAULT_KEYLENGTH);
prng.GenerateBlock( key, key.size() );

byte iv[ Blowfish::BLOCKSIZE ];
prng.GenerateBlock( iv, sizeof(iv) );

vector<string> vv;
vv.push_back("String 1");
vv.push_back("String 2");
vv.push_back("String 3");
vv.push_back("String 4");
vv.push_back("String 5");

string plain, cipher, recovered;

try {

    EAX< Blowfish >::Encryption e1;
    e1.SetKeyWithIV( key, key.size(), iv, sizeof(iv) );

    for(unsigned i = 0; i < vv.size(); i++)
    {
        /*********************************\
        \*********************************/

        plain = vv[i];
        cout << "plain text: " << plain << endl;

        e1.SetKeyWithIV( key, key.size(), iv, sizeof(iv) );

        cipher.clear();
        StringSource ss1(plain, true,
                         new AuthenticatedEncryptionFilter( e1,
                             new StringSink( cipher )
                         )  ); // StringSource

        /*********************************\
        \*********************************/

        EAX< Blowfish >::Decryption d2;
        d2.SetKeyWithIV( key, key.size(), iv, sizeof(iv) );

        recovered.clear();
        StringSource ss2(cipher, true,
                         new AuthenticatedDecryptionFilter( d2,
                             new StringSink( recovered ),
                             AuthenticatedDecryptionFilter::THROW_EXCEPTION
                         ) ); // StringSource

        cout << "recovered text: " << recovered << endl;
    }

} catch (const Exception& ex) {
    cerr << ex.what() << endl;
}