wallet/src/ristretto255.h

#pragma once
//	libsodium is typeless, which I find confusing.  Everything is unsigned
//	bytes pointed at by naked pointers.  It is well written assembly language
// written in C  It is not even C written in C, let alone C++ written in C.
//
//	NaCl provides a high level C++ interface to the low level C libsodium
//	interface, but I just don't like the people running NaCl and suspect them
//	of being in bed with my enemies, whereas I do like the people running
//	LibSodium.
//
//	It is nonetheless probably stupid to write my own high level interface to
//	 LibSodium, when one has already been written, but I am going to do so
// anyway, because elliptic curves are just way cool, and because  ...
//	because ...  I am having trouble thinking up a good excuse ... ah yes,
//	because when I read the NaCl documentation it says "X has not been
//	implemented yet" when X is something that is pretty easy to implement
//	if one has direct access to elliptic curve objects, and our Merkle patricia
//	blockchain is going to be a great big pile of elliptic curve objects.
//	NaCl suffers from the chronic disease both of open source projects,
//	and also of high level interfaces to low level data structures, of getting
//	fine tuned to the implementer's pet projects, which fine tuning is apt to
//	get in the way of someone else's pet project.
//
//	LibSodium, being assembly language written in C, rather than C written
//	 in C, or C++ written in C, has the problems:
//	If you mix up the pointer to one kind of object with the pointer to
//	another kind of object, you are sol
//	If you mix up a pointer to a thirty two byte object with a pointer to a
//	sixtyfour byte object, you are really sol
//	if you reference something that has been de-allocated, you are sol.
//	If you reference something that has not been properly initialized,
//	you are sol.
//	It is all raw memory, and structure exists only in the head of the
//	programmer.  The compiler knows nothing of these structures.
//
//	That said, there is an immense amount of cryptographic knowledge
//	encapsulated in this library, and I need to lift that knowledge into the
//	language of C++20, from C that is almost assembly.
//	There is a huge amount of knowledge embedded, and translating it
//	from what is almost a machine language representation to a C++20
//	representation involves a big pile of stuff.

//	We are going to need to lift
//	https://paragonie.com/blog/2017/06/libsodium-quick-reference-quick-comparison-similar-functions-and-which-one-use or their ristretto equivalents to C++

//	Starting with ristretto points and scalars, but they are useless without a
//	pile of other things, many of those other things being in
//	https://download.libsodium.org/doc/helpers/
//	I went there to find out what the hell "sodium_is_zero" means, but
//	found a pile of other things that I am going to need, and got distracted
//	by no end of odds and ends that I am going to need to be to lift to
//	C++20 in order for ristretto points and scalars to be put to any use.


void randombytes_buf(std::span<byte> in);
void randombytes_buf(std::span<char   > in);


namespace ristretto255 {
	using
		ro::to_base64_string, ro::is_serializable,
		ro::serialize, ro::bin2hex, ro::hex2bin,
		ro::bin2hex, ro::CompileSizedString,
		ro::has_machine_independent_representation;
				;
	//	a class representing ristretto255 elliptic points
	class point;

	//	a class representing ristretto255 scalars
	class scalar;

	template<unsigned int>class hsh;
	template<unsigned int>class hash;
	template <class T>decltype(std::declval<T>().blob, bool()) ConstantTimeEqualityTest(const T& x, const T& y) {
		if (T::constant_time_required) {
			return 0 == sodium_memcmp(&x.blob[0], &y.blob[0], sizeof(x.blob));
		}
		else return x == y;
	}

	template <class T>decltype(std::declval<T>().blob, wxString()) to_wxString(const T& p_blob) {
		std::array<char, (sizeof(p_blob.blob) * 8 + 11) / 6> sz;
		bits2base64(&(p_blob.blob[0]), 0, sizeof(p_blob.blob) * 8, std::span<char>(sz));
		return wxString::FromUTF8Unchecked(&sz[0]);
	}

	//	hsh constructs a partial hash, not yet finalized
	//	normally never explicitly used in code, but rather a nameless rtype value on the stack.
	//	To which more stuff can be added with the << operator
	//	usage:
	//		hash(    hsh(a, b) << c << f << g    );
	//		assert(  hash(a, b, c, d, e) == hash(hsh(a, b, c) << d << e)  );
	// 	hash finalizes hsh.
	//	Of course you would never use it that way, because you would only
	//	use it explicitly if you wanted to keep it around
	// 	attempting hash more things into an hsh object that has already
	//  been finalized will throw an exception.
	//	Old type C byte array arguments after the first are vulnerable to
	//  array decay to pointer,	so wrap them in std::span(OldTypeCarray)
	//	or hash them using "<<" rather than putting them in the initializer.
	//	It always a wise precaution to not use old type C arays, or wrap them
	//	in a span.
	//	Old type zero terminated strings work.  The trailing zero is included
	//	in the hash, thus hash("the quick ", "brown fox") != hash("the quick brown fox")


	template<unsigned int hashsize = 256> class hsh {
	public:
		static_assert(hashsize > 63 && hashsize % 64 == 0 && crypto_generichash_BYTES_MIN * 8 <= hashsize && hashsize <= crypto_generichash_BYTES_MAX * 8, "Bad hash size.");
		static constexpr unsigned int type_indentifier = 2 + (hashsize + 0x90 * 8) / 64;
		static_assert(crypto_generichash_BYTES_MAX < 0x90, "Change in max hash has broken our type ids");
		crypto_generichash_blake2b_state st;
		hsh() {
			int i{ crypto_generichash_blake2b_init(
				&st,
				nullptr,0,
				hashsize / 8)
			};
			assert(i == 0);
		}

		template<has_machine_independent_representation T, typename... Args>
		hsh<hashsize>& hashinto(const T& j, Args... args) {
			auto sj = ro::serialize(j);
			int i = crypto_generichash_blake2b_update(
				&(this->st),
				(const unsigned char*)&sj[0],
				sj.size()
			);
			if (i) throw HashReuseException();
			if constexpr (sizeof...(args) > 0) {
				(*this).hashinto(args...);
			}
			return *this;
		}

		template<has_machine_independent_representation T> hsh<hashsize>& operator << (const T& j) {
			auto sj = ro::serialize(j);
			auto i = crypto_generichash_blake2b_update(
				&(this->st),
				(const unsigned char*)&sj[0],
				sj.size()
			);
			if (i) throw HashReuseException();
			return *this;
		}


	};
	static_assert(!has_machine_independent_representation<hsh<256> >, "Don't want to partially hash partial hashes");

	//	This constructs a finalized hash.
	//	If it has one argument, and that argument is hsh (unfinalized hash) object,
	//	it finalizes the hash.  (see hsh)
	//	Usage
	//	hash(a, b, c ...);
	// 	hash and hsh serialize all their arguments, converting them into machine
	//	and compiler independent form.  If they don't know how to serialize an
	//	argument type, you get a compile time error.  To serialize a new type,
	// 	create a new overload for the function "serialize"
	// 	to hash a wxString, use its ToUTF8 member
	// 		wxString wxsHello(L"Hello world");
	//		hash hashHello(wxsHello.ToUTF8());
	//	C array arguments after the first are vulnerable to array decay to pointer, so use hsh and "<<"
	//	for them. or wrap them in std::span(OldTypeCarray)
	//	It always a wise precaution to not use old type C arays, or wrap them
	//	in a span.
	//	Old type zero terminated utf8 strings work.  The trailing zero is included.
	//	The program should by running in the UTF8 locale, attempts to set that
	//	locale on startup. and tests for success in the unit test.
	template<unsigned int hashsize = 256> class hash {
		static_assert(
			hashsize > 63 && hashsize % 64 == 0
			&& crypto_generichash_BYTES_MIN * 8 <= hashsize
			&& hashsize <= crypto_generichash_BYTES_MAX * 8,
			"Bad hash size."
			);
		friend point;
		friend scalar;
		friend hsh<hashsize>;
	public:
		static constexpr unsigned int type_indentifier = 2 + hashsize / 64;
		hash() = default;
		std::array<uint8_t, hashsize / 8> blob;
		~hash() = default;
		hash(hash&&) = default;	// Move constructor
		hash(const hash&) = default;	// Copy constructor
		hash& operator=(hash&&) = default;	// Move assignment.
		hash& operator=(const hash&) = default;	// Copy assignment.
		explicit hash(hsh<hashsize>& in) {
			int i = crypto_generichash_blake2b_final(
				&in.st,
				&blob[0], hashsize / 8);
			assert(i == 0);
			if (i) throw HashReuseException();
		}
		template< has_machine_independent_representation T, typename... Args>explicit hash(const T& first, Args... args) {

			hsh<hashsize> in;
			in << first;
			if constexpr (sizeof...(args) > 0) {
				in.hashinto( args...);
			}
			int i = crypto_generichash_blake2b_final(
				&in.st,
				&blob[0], hashsize / 8);
			assert(i == 0);
		}
		hash& operator=(hsh<hashsize>&& in) {
			int i = crypto_generichash_blake2b_final(
				&in.st,
				&blob[0], hashsize / 8);
			if (i) throw HashReuseException();
		}
		bool operator==(const hash<hashsize>& pt) const& {
			return blob == pt.blob;	//Do not need constant time equality test on hashes
		}
		bool operator!=(const hash<hashsize>& pt) const& {
			return blob != pt.blob;	//Do not need constant time equality test on hashes
		}
	};

	//	a class representing ristretto255 elliptic points,
	//	which are conveniently of prime order.
	class point
	{
		//	We will be reading points from the database, as blobs,
		//	reading them from the network as blobs,
		//	and reading them from human entered text as base58 encoded blobs.
		//	Therefore, invalid point initialization data is all too possible.
	public:
		static constexpr unsigned int type_indentifier = 1;
		std::array<uint8_t, crypto_core_ristretto255_BYTES> blob;
		static_assert(
			std::is_trivially_copyable<std::array<uint8_t, crypto_core_ristretto255_BYTES>>(),
			"does not support memcpy init"
			);
		static_assert(sizeof(blob) == 32,
			"watch for size and alignment bugs. "
			"Everyone should standarize on 256 bit public keys except for special needs"
			);
		static point ptZero;
		static point ptBase;
		explicit point() = default;
		//	After loading a point as a blog from the network, from the database,
		//	or from user data typed as text, have to check for validity.
		bool valid(void) const { return 0 != crypto_core_ristretto255_is_valid_point(&blob[0]); }
		explicit constexpr point(std::array<uint8_t, crypto_core_ristretto255_BYTES>&& in) :
			blob{ std::forward<std::array<uint8_t, crypto_core_ristretto255_BYTES>>(in) } {  };
		static_assert(crypto_core_ristretto255_BYTES == 32, "256 bit points expected");
		~point() = default;
		point(point&&) = default;	// Move constructor
		point(const point&) = default;	// Copy constructor
		point& operator=(point&&) = default;	// Move assignment.
		point& operator=(const point&) = default;	// Copy assignment.
		bool operator==(const point& pt) const& {
			return ConstantTimeEqualityTest(*this, pt);
		}
		point operator+(const point &pt) const& {
			point me;
			auto i{ crypto_core_ristretto255_add(_Out_ & me.blob[0], &blob[0], &pt.blob[0])};
			assert(i == 0);
			if (i != 0)throw NonRandomScalarException();
			return me;
		}

		point operator-(const point& pt) const& {
			point me;
			auto i{ crypto_core_ristretto255_sub(_Out_ &me.blob[0], &blob[0], &pt.blob[0]) };
			assert(i == 0);
			if (i != 0)throw NonRandomScalarException();
			return me;
			static_assert(sizeof(blob) == 32, "alignment?");
		}

		point operator*(const scalar&) const &noexcept;
		point operator*(int) const& noexcept;

		explicit point(const hash<512>& x) noexcept {
			static_assert(crypto_core_ristretto255_HASHBYTES * 8 == 512,
				"we need 512 bit randoms to ensure our points and scalars are uniformly distributed"
				);
			//  There should be scalar from hash, not point from hash
			//	libsodium already supplies a random point
			int i{
				crypto_core_ristretto255_from_hash(&blob[0], &(x.blob)[0]) };
			assert(i == 0);
		}

		static point random(void) {
			point me;
			crypto_core_ristretto255_random(_Out_ &(me.blob[0]));
			return me;
		}

		bool operator !() const& {
			return 0 != sodium_is_zero(&blob[0], sizeof(blob));
		}

		static bool constant_time_required;

	};

	class scalar
	{
		friend point;
	public:
		static constexpr unsigned int type_indentifier = 2;
		std::array<uint8_t, crypto_core_ristretto255_SCALARBYTES> blob;
		static_assert(sizeof(blob) == 32, "watch for size and alignment bugs.  Everyone should standarize on 256 bit secret keys except for special needs");
		explicit scalar() = default;
		~scalar() = default;
		explicit constexpr scalar(std::array<uint8_t, crypto_core_ristretto255_BYTES>&& in) : blob{ in } {};
		explicit constexpr scalar(std::array<uint8_t, crypto_core_ristretto255_BYTES>* in) :blob(*in) {};
		explicit constexpr scalar(uintmax_t k){ for (auto& j : blob) { j = k; k = k >> 8; } }
		template <class T>
		explicit constexpr scalar(std::enable_if_t < ro::is_standard_unsigned_integer<T>, T> i) :scalar(uintmax_t(i)) {}
		template <class T, class U = std::enable_if_t<ro::is_standard_signed_integer<T>, uintmax_t>>
		explicit constexpr scalar(T i) : scalar(U(ro::iabs<T>(i))) {
			static_assert (ro::is_standard_signed_integer<T>);
			if (i < 0) crypto_core_ristretto255_scalar_negate(&blob[0], &blob[0]);
		}
		scalar(scalar&&) = default;	// Move constructor
		scalar(const scalar&) = default;	// Copy constructor
		scalar& operator=(scalar&&) = default;	// Move assignment.
		scalar& operator=(const scalar&) = default;	// Copy assignment.
/*		Don't need constant time equality test
		bool operator==(const scalar& sc) const& {
			return ConstantTimeEqualityTest(*this, sc);
		}*/
		std::strong_ordering operator <=>(const scalar& sc) const& noexcept;
		//	strangely, contrary to documentation, compiler generates operator>
		//	but fails to generate operator==
		bool operator==(const scalar& sc) const& = default;
		/* {
			return (*this <=> sc) == 0;
		}*/


		//bool operator!=(const scalar& sc) const& {
//			return !ConstantTimeEqualityTest(*this, sc);
//		}
		scalar operator+(const scalar sclr) const& {
			scalar me;
			crypto_core_ristretto255_scalar_add( _Out_&me.blob[0], &blob[0], &sclr.blob[0]);
			return me;
		}
		static_assert(sizeof(scalar::blob) == 32, "compiled");

		scalar multiplicative_inverse()	const &{
			scalar me;
			auto i = crypto_core_ristretto255_scalar_invert(_Out_&me.blob[0], &blob[0]);
			assert(i == 0);
			if (i != 0)throw NonRandomScalarException();
			return me;
		}

		scalar operator-(const scalar& sclr) const& {
			scalar me;
			crypto_core_ristretto255_scalar_sub(_Out_&me.blob[0], &blob[0], &sclr.blob[0]);
			return me;
		}

		scalar operator*(const scalar& sclr) const& {
			scalar me;
			crypto_core_ristretto255_scalar_mul(_Out_&me.blob[0], &blob[0], &sclr.blob[0]);
			return me;
		}

		scalar operator/(const scalar sclr) const& {
			return operator*(sclr.multiplicative_inverse());
		}

		scalar operator*(int64_t i) const& {
			return operator * (scalar(i));
		}

		point operator*(const point& pt) const& {
			point me;
			auto i{ crypto_scalarmult_ristretto255(_Out_&me.blob[0], &blob[0], &pt.blob[0]) };
			assert(i == 0);
			if (i != 0)throw NonRandomScalarException();
			return me;
		}

		point timesBase() const& {
			point me;
			auto i{ crypto_scalarmult_ristretto255_base(_Out_ & me.blob[0], &blob[0]) };
			assert(i == 0);
			if (i != 0)throw NonRandomScalarException();
			return me;
		}

		explicit scalar(const hash<512>& x) {
			static_assert(crypto_core_ristretto255_HASHBYTES == 64, "inconsistent use of magic numbers");
			crypto_core_ristretto255_scalar_reduce(&blob[0], &(x.blob)[0]);
		}

		static scalar random(void) {
			scalar me;
			crypto_core_ristretto255_scalar_random(_Out_ & me.blob[0]);
			return me;
		}

		bool valid(void) const& {
			int x = sodium_is_zero(&blob[0], crypto_core_ed25519_SCALARBYTES);
			return x==0  && *this<scOrder;
			// The libsodium library allows unreduced scalars, but I do not
			// except, of course, for scOrder itself
		}

		//	We don't need constant time equality test on scalars
		//	since they normally appear in signatures, or are
		//	checked against a hash or a point
		/*bool operator !() const& {
			return 0 != sodium_is_zero(&blob[0], sizeof(blob));
		}*/

/*		explicit operator wxString() const&;
		explicit operator std::string() const&;*/
		static bool constant_time_required;
		static const scalar& scOrder;

	private:
		void reverse(std::array < uint8_t, crypto_core_ristretto255_SCALARBYTES>const& ac) {
			auto p = blob.rbegin();
			for (auto x : ac) {
				*p++ = x;
			}
		}
	};

	static_assert(ro::blob_type<scalar> && !ro::blob_type<int>);
	static_assert(ro::is_blob_field_type<scalar>::value);
	static_assert(ro::is_blob_field_type<scalar&>::value);
	static_assert(ro::is_blob_field_type<point>::value);
	static_assert(ro::is_blob_field_type<hash<256> >::value);
	static_assert(false == ro::is_blob_field_type<char*>::value);
	static_assert(ro::has_machine_independent_representation<scalar&>);
	static_assert(ro::has_machine_independent_representation<hash<512>&>);
	static_assert(ro::is_blob_field_type<int>::value == false);
	static_assert(ro::has_machine_independent_representation<unsigned int>);
	static_assert(ro::has_machine_independent_representation<char*>);
	static_assert(ro::has_machine_independent_representation<uint8_t*> == false); //false because uint8_t * has no inband terminator
	static_assert(false == ro::has_machine_independent_representation<wxString> && !ro::is_constructible_from_v<hash<256>, wxString>, "wxStrings are apt to convert anything to anything, with surprising and unexpected results");
	static_assert(ro::has_machine_independent_representation<decltype(std::declval<wxString>().ToUTF8())> == true);
	static_assert(ro::is_constructible_from_all_of<scalar, int, hash<512>, std::array<uint8_t, crypto_core_ristretto255_BYTES>>);
	static_assert(ro::is_constructible_from_all_of<hash<256>, char*, short, unsigned short, hash<512>, point, scalar>, "want to be able to hash anything has_machine_independent_representation");
	static_assert(false == ro::is_constructible_from_any_of<int, scalar, point, hsh<512>, hash<256>>);
	static_assert(false == ro::is_constructible_from_any_of <scalar, wxString, hash<256>, byte*>, "do not want indiscriminate casts");
	static_assert(false == ro::is_constructible_from_any_of <point, wxString, hash<256>, byte*>, "do not want indiscriminate casts ");
	static_assert(false == ro::is_constructible_from_v<hash<256>, float>);
	static_assert(ro::has_machine_independent_representation<float> == false);//Need to convert floats to
		//	their machine independent representation, possibly through idexp, frexp
		//	 and DBL_MANT_DIG
	static_assert(sizeof(decltype(ro::serialize(std::declval<scalar>())[0])) == 1);
	static_assert (std::is_standard_layout<scalar>(), "scalar for some reason is not standard layout");
	static_assert (std::is_trivial<scalar>(), "scalar for some reason is not trivial");
	static_assert(sizeof(point) == 32, "funny alignment");
	static_assert(sizeof(scalar) == 32, "funny alignment");

	class signed_text {
	public:
		std::span<char> txt;
		scalar c;
		scalar s;
		point K;
		signed_text(
			const scalar&,	//	Signer's secret key
			const point&,	//	Signer's public key
			std::span<char>	//	Text to be signed.
		);
		bool verify();
	};

	class CMasterSecret :public scalar {
	public:
		CMasterSecret() = default;
		CMasterSecret(const scalar& pt) :scalar(pt) {}
		CMasterSecret(const scalar&& pt) :scalar(pt) {}
		CMasterSecret(CMasterSecret&&) = default;	// Move constructor
		CMasterSecret(const CMasterSecret&) = default;	// Copy constructor
		CMasterSecret& operator=(CMasterSecret&&) = default;	// Move assignment.
		CMasterSecret& operator=(const CMasterSecret&) = default;	// Copy assignment.
		template<class T> auto operator()(T psz) {
			scalar& t(*this);
			return scalar(hash<512>(t, psz));
		}

	};


} //End ristretto255 namespace

//	Ristretto255 scalars are defined to be little endian on all hardware
//	regardless of the endianess of the underlying hardware.
//	though it is entirely possible that sometime in the future, this
//	definition will be changed should big endian hardware ever be
//	sufficiently popular for anyone to care.
//	So, because scalars are in fact integers, displaying them as
//	biendian on all hardware when displayed in hex
//	or base64.  Everything else gets displayed in memory order.
template<> ristretto255::scalar ro::hex2bin	<ristretto255::scalar		  >(const ro::CompileSizedString< (2 * sizeof(ristretto255::scalar))>&);
template<> ro::CompileSizedString< (2 * sizeof(ristretto255::scalar))		> ro::bin2hex<ristretto255::scalar>(const ristretto255::scalar&);
template<> ro::CompileSizedString< (8 * sizeof(ristretto255::scalar) + 5) / 6> ro::to_base64_string	<ristretto255::scalar>(const ristretto255::scalar&);