My doubt about CBC_

[Yongce]

Hi All,

I am confused by CBC_CTS_Mode.

Here is my program.
----------------------------------------------------------------------------------------------------------
#include <iostream>
#include <cryptopp/aes.h>
#include <cryptopp/modes.h>
#include <cryptopp/filters.h>
#include <cryptopp/hex.h>
#include <cryptopp/files.h>

using namespace std;
using namespace CryptoPP;

int main()
{
    string message = "this is a message for testing";
    string ciphertext;
    string messageRecovered;

    cout << "Plaintext (" << message.size() << " bytes):\n\t" <<
message << '\n';

    byte key[AES::DEFAULT_KEYLENGTH], iv[AES::BLOCKSIZE];
    ::memset(key, 0x01, sizeof(key));
    ::memset(iv, 0x11, sizeof(iv));

    CBC_CTS_Mode<AES>::Encryption encryptor(key,
AES::DEFAULT_KEYLENGTH, iv);
    StringSource(message, true, new StreamTransformationFilter(
        encryptor, new StringSink(ciphertext)));

    cout << "Ciphertext (" << ciphertext.size() << " bytes):\n\t";
    StringSource(ciphertext, true, new HexEncoder(new
FileSink(cout)));
    cout << '\n';

    CBC_CTS_Mode<AES>::Decryption decryptor(key,
AES::DEFAULT_KEYLENGTH, iv);
    StringSource(ciphertext, true, new StreamTransformationFilter(
        decryptor, new StringSink(messageRecovered)));

    cout << "Plaintext recovered (" << messageRecovered.size() << "
bytes):\n\t";
    cout << messageRecovered << endl;

    return 0;
}
--------------------------------------------------------------------------------------------------------------------

The running result:
-------------------------------------------------------------------------------------------------------------------
Plaintext (29 bytes):
        this is a message for testing
Ciphertext (29 bytes):
        8383CA42A94C7781D0ACA5BECB663F7CFA8DE5CB20080DCB329C96825B
Plaintext recovered (29 bytes):
        this is a message for testing
-------------------------------------------------------------------------------------------------------------------

I thought CBC_CTS_Mode was block-oriented, right?
And I thought length of the outputed cipher should be 32 bytes, but
the result was not.

If I use CBC_CTS_Mode to process data directly (not by
StreamTransformationFilter),
I can only process data with length of multiple block size.

They seems to be conflicting with each other? What's wrong with this?

Regards,
Yongce
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