Problem with AES in CFB mode

[Jeffrey Walton]

Hi All,

Using Crypto++ 5.1, MSVC++ 6.0 SP5, Processor Pack installed.

When I change to CFB mode (from CBC mode), the following demo breaks. How does 
one instruct the StreamTransformationFilter to pad? I must have missed it in 
the documentation.

Thanks,
Jeff


CryptoPP::CBC_Mode_ExternalCipher::... // OK
to
CryptoPP::CFB_Mode_ExternalCipher::... // Breaks

*******************************************
*******************************************
#include <iostream>

#include "modes.h"
#include "aes.h"
#include "filters.h"

int main(int argc, char* argv[]) {

    //
    // Key and IV setup
    //
    byte key[ CryptoPP::AES::DEFAULT_KEYLENGTH ], iv[ CryptoPP::AES::BLOCKSIZE 
];
    memset( key, 0x01, CryptoPP::AES::DEFAULT_KEYLENGTH );
    memset( iv, 0x01, CryptoPP::AES::BLOCKSIZE );

    //
    // String and Sink setup
    //
    std::string plaintext = "Now is the time for all good men to come to the 
aide...";
    std::string ciphertext;
    std::string decryptedtext;

    //
    // Dump Plain Text
    //
    std::cout << "Plain Text (" << plaintext.size() << " bytes)" << std::endl;
    std::cout << plaintext;
    std::cout << std::endl << std::endl;

    //
    // Create Cipher Text
    //
    CryptoPP::AES::Encryption aesEncryption(key, 
CryptoPP::AES::DEFAULT_KEYLENGTH);
    CryptoPP::CBC_Mode_ExternalCipher::Encryption cbcEncryption( aesEncryption, 
iv );

    CryptoPP::StreamTransformationFilter stfEncryptor(cbcEncryption, new 
CryptoPP::StringSink( ciphertext ) );
    stfEncryptor.Put( reinterpret_cast<const unsigned char*>( plaintext.c_str() 
), plaintext.length() + 1 );
    stfEncryptor.MessageEnd();

    //
    // Dump Cipher Text
    //
    std::cout << "Cipher Text (" << ciphertext.size() << " bytes)" << std::endl;

    for( int i = 0; i < ciphertext.size(); i++ ) {
        std::cout << "0x" << (0xFF & (unsigned int)ciphertext[i]) << " ";
    }
    std::cout << std::endl << std::endl;

    //
    // Decrypt
    //
    CryptoPP::AES::Decryption aesDecryption(key, 
CryptoPP::AES::DEFAULT_KEYLENGTH);
    CryptoPP::CBC_Mode_ExternalCipher::Decryption cbcDecryption( aesDecryption, 
iv );

    CryptoPP::StreamTransformationFilter stfDecryptor(cbcDecryption, new 
CryptoPP::StringSink( decryptedtext ) );
    stfDecryptor.Put( reinterpret_cast<const unsigned char*>( 
ciphertext.c_str() ), ciphertext.size() );
    stfDecryptor.MessageEnd();

    //
    // Dump Decrypted Text
    //
    std::cout << "Decrypted Text: " << std::endl;
    std::cout << decryptedtext;
    std::cout << std::endl << std::endl;

    return 0;
}