fortuna/generator.cpp

#ifndef FORTUNA_GENERATOR_CPP
#define FORTUNA_GENERATOR_CPP

#include "generator.h"
#include "util.h"

#include <cryptopp/hex.h>
#include <cryptopp/filters.h>
#include <cryptopp/serpent.h>
#include <cryptopp/ccm.h>
#include <fmt/core.h>

#include <cmath>
#include <cassert>
#include <stdexcept>

namespace fortuna {
namespace generator {

Generator::Generator() /*noexcept*/ {
	try {
		initialize_generator();
	} catch(CryptoPP::Exception& e) {
		fmt::print(stderr, "{}\n", e.what());
		exit(1);
	}
}
Generator::~Generator() noexcept {};


void Generator::initialize_generator(){
	try {
		std::memset(G.k, 0x00, G.k.size());
		G.ctr = 0;
		fmt::print("Generator initialized\n");
	} catch(CryptoPP::Exception& e) {
		fmt::print(stderr, "{}\n", e.what());
		exit(1);
	}
}

auto Generator::get_state() const -> G_state {
	return G;
}

auto Generator::time_to_reseed() const -> bool {
	// TODO(me): implement this
	if (true) {
		return true;
	} else {
		return false;
	}
}

auto Generator::reseed(const std::string& s) -> void {
	// ref: https://www.cryptopp.com/wiki/SecBlock
	std::string da_key(reinterpret_cast<const char*>(&G.k[0]),
						G.k.SizeInBytes() * 8); // we need the size in bits

	try {
		std::lock_guard<std::mutex> lg(mtx);
		std::string a{fortuna::Util::do_sha(da_key + s)};
		std::memmove(G.k, a.c_str(), G.k_length);
		++G.ctr;
		fmt::print("[i] generator: reseeded\n");
	} catch(std::exception& e) {
		fmt::print("{}", e.what());
	}
}

auto Generator::do_crypto() -> std::string {
	/* this function calls the block cipher
	 * returns a string of k*(16 bytes);
	 * do whatever atm */

	// for the moment loosely based on
	// https://www.cryptopp.com/wiki/CTR_Mode
	using CryptoPP::StringSource;
	using CryptoPP::StringSink;
	using CryptoPP::HexEncoder;
	using CryptoPP::StreamTransformationFilter;
	using CryptoPP::Serpent;
	using CryptoPP::CTR_Mode;

	// William Shakespeare, Romeo and Juliet
	std::string plain{"Oh, I am fortune's fool!"};
	std::string cipher, encoded_c;
	// in case we need to convert counter to string
	std::string str_ctr{reinterpret_cast<const char*>(&G.ctr)};
	// 16 bytes --> 128bit
	static constexpr const std::size_t ctr_length{16};
	CryptoPP::FixedSizeSecBlock<CryptoPP::byte, ctr_length> ctr;
	std::memmove(ctr, str_ctr.c_str(), ctr_length);

	try {
		CTR_Mode<Serpent>::Encryption e;
		e.SetKeyWithIV(G.k,G.k.size(),ctr);

		// The StreamTransformationFilter adds padding as required. ECB and
		// CBC Mode must be padded to the block size of the cipher. CTR
		// mode not.
		// the "true" param - pump all of the data immediately to its
		// attached transformation
		StringSource str_src1(plain,true,
			new StreamTransformationFilter(e,
				new StringSink(cipher)
			) // StreamTransformationFilter
		); // StringSource
	}
	catch(CryptoPP::Exception& e) {
		fmt::print(stderr, "{}\n", e.what());
		exit(1);
	}

	// Pretty print cipher text
	StringSource str_src2(cipher,true,
		new HexEncoder(
			new StringSink(encoded_c)
		) // HexEncoder
	); // StringSource

	return encoded_c;
}

auto Generator::generate_blocks(unsigned int k_blocks) -> std::string {
	assert ((G.ctr!=0) && "Counter is not 0, generator has been seeded");
	std::string r{""};
	for (int i = 0; i < k_blocks; ++i) {
		r += do_crypto();
		++G.ctr;
	}
	return r;
}

auto Generator::generate_random_data(uint n) -> std::string {
	std::lock_guard<std::mutex> lg(mtx);
	// fmt::print("n -> {}\n", n); // debugging
	if (n == 0) {
		// do not do this..?
		const std::string msg{"zero bytes requested, bailing\n"};
		fmt::print("[*] error: {}", msg);
		throw std::invalid_argument(msg);
	}

	// pre-computed 2^20
	if (n > 1048576) {
		const std::string msg{"n cannot be > 2^20\n"};
		fmt::print("[*] error: {}", msg);
		throw std::invalid_argument(msg);
	}

	std::string r;

	try {
		/* do magic to compute r
		* r ← first-n-bytes(GenerateBlocks(G, ceil(n/16) )) */
		// n is number of bytes, i.e. pass n*8 to get number of bits
		unsigned int how_many(static_cast<unsigned int>(ceil((n*8)/16)));
		// fmt::print("how_many: {}\n", how_many); // debugging
		std::string rr{generate_blocks(how_many)};
		fmt::print("rr (output from generate_blocks): {}\n", rr);

		// since we're truncating hex, we need to get twice more characters
		r = rr.substr(0,n*0x02ul);
		rr.clear();
	} catch(std::exception& e) {
		fmt::print("{}", e.what());
	}

	/* re-key */
	try {
		std::string nu_G_k{generate_blocks(2)};
		// fmt::print("nu_G_k: {}\n", nu_G_k); // debugging
		std::string dst;
		// FIXME: +1 for the actual null-termination, not exactly sure if needed
		dst.resize(G.k_length + 1);
		CryptoPP::StringSource str_s(
			nu_G_k,true,new CryptoPP::HexDecoder(new CryptoPP::StringSink(dst))
		);

		nu_G_k.clear();

		/* clear out the old key and set a new one */
		std::memset(G.k, 0x00, G.k_length);
		std::memmove(G.k, dst.c_str(), G.k_length);
	} catch(std::exception& e) {
		fmt::print("{}", e.what());
	}
	return r;
}



} // namespace generator
} // namespace fortuna
#endif