Hi All,
I'm using AES in CTR mode. After I encrypt a block of data (happens to
be of size AES::BLOCKSIZE), I get a random IV back on a call to
GetNextIV(). Is there a way to get the next counter back?
I'm trying to verify my management of the counter value is consistent
with Crypto++'s management of the counter.
Jeff
///////////////////////////////////////
// Key and Counter
///////////////////////////////////////
byte key[ CryptoPP::AES::DEFAULT_KEYLENGTH ];
byte counter[ CryptoPP::AES::BLOCKSIZE ];
byte next[ CryptoPP::AES::BLOCKSIZE ]; // next counter
::memset( key, 0xAA, CryptoPP::AES::DEFAULT_KEYLENGTH );
::memset( counter, 0x00, CryptoPP::AES::BLOCKSIZE );
///////////////////////////////////////
// Sources and Sinks
///////////////////////////////////////
// Message M
std::string PlainText;
// Cipher Text Sink
std::string CipherText;
// Recovered Text Sink
std::string RecoveredText;
///////////////////////////////////////
// Random Data
///////////////////////////////////////
CryptoPP::AutoSeededRandomPool rng;
CryptoPP::RandomNumberSource( rng,
CryptoPP::AES::BLOCKSIZE,
true, new CryptoPP::StringSink( PlainText )
);
///////////////////////////////////////
// Encryption
///////////////////////////////////////
CryptoPP::CTR_Mode< CryptoPP::AES >::Encryption Encryptor;
Encryptor.SetKeyWithIV( key, sizeof(key), counter );
CryptoPP::StringSource( PlainText, true,
new CryptoPP::StreamTransformationFilter(
Encryptor,
new CryptoPP::StringSink( CipherText )
) // StreamTransformationFilter
); // StringSource
///////////////////////////////////////
// Next Counter Value
///////////////////////////////////////
Encryptor.GetNextIV( NullRng, next );
...
std::string scratch;
CryptoPP::ArraySource(
(const byte*)next, CryptoPP::AES::BLOCKSIZE, true,
new CryptoPP::HexEncoder(
new CryptoPP::StringSink( scratch ), true, 2
)
);
cout << "Next Counter: " << endl;
cout << scratch << endl;
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