//
// PBKDF2Engine.h
//
// Library: Foundation
// Package: Crypt
// Module:  PBKDF2Engine
//
// Definition of the PBKDF2Engine class.
//
// Copyright (c) 2014, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// SPDX-License-Identifier:	BSL-1.0
//


#ifndef Foundation_PBKDF2Engine_INCLUDED
#define Foundation_PBKDF2Engine_INCLUDED


#include <algorithm>
#include "Poco/ByteOrder.h"
#include "Poco/DigestEngine.h"
#include "Poco/Foundation.h"


namespace Poco
{


template <class PRF>
class PBKDF2Engine : public DigestEngine
/// This class implements the Password-Based Key Derivation Function 2,
/// as specified in RFC 2898. The underlying DigestEngine (HMACEngine, etc.),
/// which must accept the passphrase as constructor argument (std::string),
/// must be given as template argument.
///
/// PBKDF2 (Password-Based Key Derivation Function 2) is a key derivation function
/// that is part of RSA Laboratories' Public-Key Cryptography Standards (PKCS) series,
/// specifically PKCS #5 v2.0, also published as Internet Engineering Task Force's
/// RFC 2898. It replaces an earlier standard, PBKDF1, which could only produce
/// derived keys up to 160 bits long.
///
/// PBKDF2 applies a pseudorandom function, such as a cryptographic hash, cipher, or
/// HMAC to the input password or passphrase along with a salt value and repeats the
/// process many times to produce a derived key, which can then be used as a
/// cryptographic key in subsequent operations. The added computational work makes
/// password cracking much more difficult, and is known as key stretching.
/// When the standard was written in 2000, the recommended minimum number of
/// iterations was 1000, but the parameter is intended to be increased over time as
/// CPU speeds increase. Having a salt added to the password reduces the ability to
/// use precomputed hashes (rainbow tables) for attacks, and means that multiple
/// passwords have to be tested individually, not all at once. The standard
/// recommends a salt length of at least 64 bits. [Wikipedia]
///
/// The PBKDF2 algorithm is implemented as a DigestEngine. The passphrase is specified
/// by calling update().
///
/// Example (WPA2):
///     PBKDF2Engine<HMACEngine<SHA1Engine> > pbkdf2(ssid, 4096, 256);
///     pbkdf2.update(passphrase);
///     DigestEngine::Digest d = pbkdf2.digest();
{
public:
    enum
    {
        PRF_DIGEST_SIZE = PRF::DIGEST_SIZE
    };

    PBKDF2Engine(const std::string & salt, unsigned c = 4096, Poco::UInt32 dkLen = PRF_DIGEST_SIZE) : _s(salt), _c(c), _dkLen(dkLen)
    {
        _result.reserve(_dkLen + PRF_DIGEST_SIZE);
    }

    ~PBKDF2Engine() { }

    std::size_t digestLength() const { return _dkLen; }

    void reset()
    {
        _p.clear();
        _result.clear();
    }

    const DigestEngine::Digest & digest()
    {
        Poco::UInt32 i = 1;
        while (_result.size() < _dkLen)
        {
            f(i++);
        }
        _result.resize(_dkLen);
        return _result;
    }

protected:
    void updateImpl(const void * data, std::size_t length) { _p.append(reinterpret_cast<const char *>(data), length); }

    void f(Poco::UInt32 i)
    {
        PRF prf(_p);
        prf.update(_s);
        Poco::UInt32 iBE = Poco::ByteOrder::toBigEndian(i);
        prf.update(&iBE, sizeof(iBE));
        Poco::DigestEngine::Digest up = prf.digest();
        Poco::DigestEngine::Digest ux = up;
        poco_assert_dbg(ux.size() == PRF_DIGEST_SIZE);
        for (unsigned k = 1; k < _c; k++)
        {
            prf.reset();
            prf.update(&up[0], up.size());
            Poco::DigestEngine::Digest u = prf.digest();
            poco_assert_dbg(u.size() == PRF_DIGEST_SIZE);
            for (int ui = 0; ui < PRF_DIGEST_SIZE; ui++)
            {
                ux[ui] ^= u[ui];
            }
            std::swap(up, u);
        }
        _result.insert(_result.end(), ux.begin(), ux.end());
    }

private:
    PBKDF2Engine();
    PBKDF2Engine(const PBKDF2Engine &);
    PBKDF2Engine & operator=(const PBKDF2Engine &);

    std::string _p;
    std::string _s;
    unsigned _c;
    Poco::UInt32 _dkLen;
    DigestEngine::Digest _result;
};


} // namespace Poco


#endif // Foundation_PBKDF2Engine_INCLUDED