fortuna/generator.cpp

#ifndef FORTUNA_GENERATOR_CPP
#define FORTUNA_GENERATOR_CPP

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

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

#include <algorithm>
#include <atomic>
#include <cassert>
#include <chrono>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <mutex>
#include <stdexcept>

namespace fortuna {
namespace generator {

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


void Generator::initialize_generator() {
	std::lock_guard<std::recursive_mutex> lg(mtx);

	try {
		std::memset(G.k, 0x00, G.k.size());
		std::memset(G.ctr.begin(), 0x00, this->ctr_len);
		fmt::print(stderr, "Generator initialized\n");
	}
	catch (CryptoPP::Exception& e) {
		fmt::print(stderr, "{}\n", e.what());
		throw;
	}
}

auto Generator::get_state() const -> G_state {
	std::lock_guard<std::recursive_mutex> lg(mtx);

	return G;
}

auto Generator::time_to_reseed(
	const uint64_t& pool0_len,
	const unsigned int& min_p_size,
	const std::chrono::duration<int64_t, std::ratio<1, 1000>>& time_elapsed,
	const std::chrono::milliseconds& gen_reseed_interval) const -> bool {
	std::lock_guard<std::recursive_mutex> lg(mtx);

	return (pool0_len >= min_p_size && time_elapsed > gen_reseed_interval);
}

auto Generator::reseed(const std::string& s) -> void {
	std::lock_guard<std::recursive_mutex> lg(mtx);
	std::unique_lock<std::mutex> ul(reseed_mtx);

	// 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::string a{fortuna::Util::do_sha(da_key + s)};
		std::memmove(G.k, fortuna::Util::de_hex(a).c_str(), G.k_length);
		Generator::ctr_inc();
		fmt::print(stderr, "[i] generator: reseeded\n");
	}
	catch (std::exception& e) {
		fmt::print(stderr, "{}\n", e.what());
		throw;
	}
}

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

	std::lock_guard<std::recursive_mutex> lg(mtx);

	// for the moment loosely based on
	// https://www.cryptopp.com/wiki/CTR_Mode

	// William Shakespeare, Romeo and Juliet
	const std::string plain{"Oh, I am fortune's fool!"};
	std::string cipher, encoded_c;
	std::unique_lock<std::mutex> ul(crypt_mtx);
	CryptoPP::FixedSizeSecBlock<CryptoPP::byte, Generator::ctr_len> ctr;
	std::memmove(ctr, G.ctr.data(), Generator::ctr_len);

	try {
		this->enc.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
		CryptoPP::StringSource str_src1(
			plain,
			true,
			new CryptoPP::StreamTransformationFilter(
				this->enc,
				new CryptoPP::StringSink(cipher)) // StreamTransformationFilter
		); // StringSource
	}
	catch (CryptoPP::Exception& e) {
		fmt::print(stderr, "{}\n", e.what());
		throw;
	}

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

	return encoded_c;
}

auto Generator::generate_blocks(unsigned int k_blocks) -> std::string {
	std::lock_guard<std::recursive_mutex> lg(mtx);

	assert((G.ctr != this->null_blk) &&
		   "Counter is not 0, generator has been seeded");
	if (!this->is_seeded()) {
		throw std::logic_error("G.ctr == 0, generator has not been seeded!");
	}

	std::string r{""};
	while (k_blocks--) {
		r += Generator::do_crypto();
		Generator::ctr_inc();
	}
	return r;
}

auto Generator::generate_random_data(const unsigned int& n) -> std::string {
	std::lock_guard<std::recursive_mutex> lg(mtx);

	if (n == 0) {
		// const std::string msg{"zero bytes requested, bailing\n"};
		fmt::print(stderr, "[!] error: zero bytes requested, bailing\n");
		// throw std::invalid_argument(msg);
		// TODO(me): throw or not?
		// perhaps just return prematurely
		return "";
	}

	// pre-computed 2^20
	if (n > 1048576) {
		throw std::invalid_argument("[!] error: n cannot be > 2^20\n");
	}

	std::string r;

	try {
		/* do magic to compute r
		 * r ← first-n-bytes(GenerateBlocks(G, ceil(n/16) )) */

		unsigned int how_many(
			static_cast<unsigned int>(std::ceil(static_cast<double>(n) / 16)));

		std::string rr{generate_blocks(how_many)};
		fmt::print(stderr, "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(stderr, "{}", 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{fortuna::Util::de_hex(nu_G_k)};

		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(stderr, "{}", e.what());
	}
	return r;
}

auto Generator::ctr_inc() -> void {
	// increment the least-significant-byte-first ctr

	std::atomic<uint8_t> i{0};
	while (true) {
		this->G.ctr.at(i) = static_cast<std::byte>(
			static_cast<uint8_t>(this->G.ctr.at(i)) + 0x01);

		if (this->G.ctr.at(i) == static_cast<std::byte>(0x00) &&
			++i < this->G.ctr.size()) {
			continue;
		}
		break;
	}
}


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