Crypto++ 5.6.3rc5 GenerateBlock Not Implemented - c++

Question

I am trying to derive key from password and want to generate randomly the salt(I dont know what size it should be for SHA-256 and does this matter like the IV in AES256, where it should be 128 bit,give a hint if someone know) with AutoSeededRandomPool but exception is cought
RandomNumberGenerator:GenerateBlock Not Implemented
I am using crypto++ 5.6.3rc5 with QT 5.5.1 and /MD release mode, this may be a bug, or unfinished work of someone.
#include <QCoreApplication>
#include <sha.h>
#include <base64.h>
#include <iostream>
#include <string>
#include <pwdbased.h>
#include <cstdio>
#include <iostream>
#include <osrng.h>
using CryptoPP::AutoSeededRandomPool;
#include <iostream>
using std::cout;
using std::cerr;
using std::endl;
#include <string>
using std::string;
#include <cstdlib>
using std::exit;
#include <cryptlib.h>
using CryptoPP::Exception;
#include <hex.h>
using CryptoPP::HexEncoder;
using CryptoPP::HexDecoder;
#include <filters.h>
using CryptoPP::StringSink;
//#include <stdlib.h>
#include <time.h>
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
try
{
AutoSeededRandomPool rng;
byte salt[16*8];
rng.GenerateBlock(salt, 16*8);
byte password[] ="password";
size_t plen = strlen((const char*)password);
size_t slen = strlen((const char*)salt);
int c = 1;
byte derived[32];
CryptoPP::PKCS5_PBKDF2_HMAC<CryptoPP::SHA256> pbkdf2;
pbkdf2.DeriveKey(derived, sizeof(derived), 0, password, plen, salt, slen, c);
string result;
HexEncoder encoder(new StringSink(result));
encoder.Put(derived, sizeof(derived));
encoder.MessageEnd();
cout << "Derived: " << result << endl;
}
catch (const Exception& ex) {
cerr << ex.what() << endl;
}
return a.exec();
}

Answer 1

Crypto++ 5.6.3rc5 GenerateBlock Not Implemented
...
You can read the history on the change at Crash in RandomNumberGenerator::GenerateWord32 due to stack recursion. The change was eventually backed out.
It was fixed in RC6, but it has not been announced yet. There's a quasi-pre-RC6 at Crypto++ 5.6.3 Files. But as soon as it is announced, then its set in stone and will not be changed.
Right now, RC6 is undergoing minor changes due to Cygwin, MinGW and C++11 on Debian Unstable. The changes are not too bad, but testing them is painful. Some of the scripts take half a day to run under emulated platforms, like S/390x.
If you want to side step the issue and avoid the download of pre-RC6, then you can use one of the following generators. They call GenerateIntoBufferedTransformation:
AutoSeededX917RNG< AES >
X917RNG
RandomPool
Or, you can use OS_GenerateRandomBlock to draw directly from the OS's pool.
Or, you can remove the code that throws. Open cryptlib.h, find RandomNumberGenerator, remove the #if 0/#endif guarding the old code and delete the throw.
Also see RandomNumberGenerator on the Crypto++ wiki.