RC6

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RC6 is a block cipher based on RC5 designed by Ron Rivest, Matt Robshaw, Ray Sidney, and Yiqun Lisa Yin. The cipher was a candidate in the Advanced Encryption Standard (AES) competition.

If your project is using encryption alone to secure your data, encryption alone is usually not enough. Please take a moment to read Authenticated Encryption and understand why you should prefer to use CCM, GCM, or EAX over other modes, such as CBC or CTR.

Sample Programs

The first snippet dumps the minimum, maximum, and default key lengths used by RC6.

cout << "key length: " << RC6::DEFAULT_KEYLENGTH << endl;
cout << "key length (min): " << RC6::MIN_KEYLENGTH << endl;
cout << "key length (max): " << RC6::MAX_KEYLENGTH << endl;
cout << "block size: " << RC6::BLOCKSIZE << endl;

Output from the above snippet produces the following. Notice the default key size is 128 bits or 16 bytes.

key length: 16
key length (min): 16
key length (max): 32
block size: 16

The following program demonstrates CBC encryption using RC6. The key is declared on the stack using a SecByteBlock to ensure the sensitive material is zeroized. Similar could be used for both plain text and recovered text.

AutoSeededRandomPool prng;

SecByteBlock key(RC6::DEFAULT_KEYLENGTH);
prng.GenerateBlock(key, key.size());

byte iv[RC6::BLOCKSIZE];
prng.GenerateBlock(iv, sizeof(iv));

string plain = "CBC Mode Test";
string cipher, encoded, recovered;

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

try
{
    cout << "plain text: " << plain << endl;

    CBC_Mode< RC6 >::Encryption e;
    e.SetKeyWithIV(key, key.size(), iv);

    // The StreamTransformationFilter adds padding
    //  as required. ECB and CBC Mode must be padded
    //  to the block size of the cipher.
    StringSource(plain, true, 
        new StreamTransformationFilter(e,
            new StringSink(cipher)
        ) // StreamTransformationFilter
    ); // StringSource
}
catch(const CryptoPP::Exception& e)
{
    cerr << e.what() << endl;
    exit(1);
}

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

// Pretty print
StringSource(cipher, true,
    new HexEncoder(
        new StringSink(encoded)
    ) // HexEncoder
); // StringSource

cout << "cipher text: " << encoded << endl;

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

try
{
    CBC_Mode< RC6 >::Decryption d;
    d.SetKeyWithIV(key, key.size(), iv);

    // The StreamTransformationFilter removes
    //  padding as required.
    StringSource s(cipher, true, 
        new StreamTransformationFilter(d,
            new StringSink(recovered)
        ) // StreamTransformationFilter
    ); // StringSource

    cout << "recovered text: " << recovered << endl;
}
catch(const CryptoPP::Exception& e)
{
    cerr << e.what() << endl;
    exit(1);
}

A typical output is shown below. Note that each run will produce different results because the key and initialization vector are randomly generated.

$ ./Driver.exe
key: 62A4A0234EE404102848A3E914B76BEE
iv: E49B294B0FD7A18C22EBDE4C0C8DDD56
plain text: CBC Mode Test
cipher text: EF2FEAEEDC5EB0310A55C0DC9C936450
recovered text: CBC Mode Test

By switching to EAX mode, authenticity assurances can placed on the cipher text for nearly no programming costs. Below the StreamTransformationFilter was replaced by AuthenticatedEncryptionFilter and AuthenticatedDecryptionFilter.

EAX< RC6 >::Encryption e;
e.SetKeyWithIV(key, key.size(), iv);

StringSource(plain, true, 
    new AuthenticatedEncryptionFilter(e,
        new StringSink(cipher)
    ) // StreamTransformationFilter
); // StringSource

...

EAX< RC6 >::Decryption d;
d.SetKeyWithIV(key, key.size(), iv);

StringSource s(cipher, true, 
    new AuthenticatedDecryptionFilter(d,
        new StringSink(recovered)
    ) // StreamTransformationFilter
); // StringSource

Typical output is as follows. Notice the additional cipher text bytes due to the MAC bytes. See EAX Mode for details.

$ ./Driver.exe
key: AF5E6C25606E87BDEB4F4E8FB5E615F0
iv: 5F089247D45BC7306F7594FDF8B66558
plain text: EAX Mode Test
cipher text: 8D23C87A7C28D1AEBE0BD53865E2D5A0FA79BDFB41433F6DA0799DD992
recovered text: EAX Mode Test

To manually insert bytes into the filter, perform multiple Puts. Though Get is used below, a StringSink could easily be attached and save the administrivia.

const size_t SIZE = 16 * 4;
string plain(SIZE, 0x00);

for(size_t i = 0; i < plain.size(); i++)
    plain[i] = 'A' + (i%26);
...

CBC_Mode < RC6 >::Encryption encryption(key, sizeof(key), iv);
StreamTransformationFilter encryptor(encryption, NULL);

for(size_t j = 0; j < plain.size(); j++)
    encryptor.Put((byte)plain[j]);

encryptor.MessageEnd();
size_t ready = encryptor.MaxRetrievable();

string cipher(ready, 0x00);
encryptor.Get((byte*) &cipher[0], cipher.size());

Downloads

RC6-CBC-Filter.zip - Demonstrates encryption and decryption using RC6 in CBC mode with filters (confidentiality only)

RC6-CTR-Filter.zip - Demonstrates encryption and decryption using RC6 in CTR mode with filters (confidentiality only)

RC6-GCM-Filter.zip - Demonstrates encryption and decryption using RC6 in GCM mode with filters (confidentiality and authenticity)

RC6-EAX-Filter.zip - Demonstrates encryption and decryption using RC6 in EAX mode with filters (confidentiality and authenticity)