@xmr-core/xmr-crypto-utils/src/crypto-ops/rct.ts

Core crypto operations for Monero and implementations and interfaces of various hardware devices for creating Monero transactions securely

import {
	ge_double_scalarmult_base_vartime,
	sc_sub,
	sc_add,
	ge_scalarmult,
} from "./primitive_ops";
import { H, I } from "./constants";
import { valid_hex } from "@xmr-core/xmr-str-utils";
import { hash_to_scalar } from "./hash_ops";
import { derivation_to_scalar, generate_key_derivation } from "./derivation";
import { Commit, Keys } from "../types";
import { HWDevice, LedgerDevice } from "../device";

//creates a Pedersen commitment from an amount (in scalar form) and a mask
//C = bG + aH where b = mask, a = amount
export function commit(amount: string, mask: string) {
	if (
		!valid_hex(mask) ||
		mask.length !== 64 ||
		!valid_hex(amount) ||
		amount.length !== 64
	) {
		throw Error("invalid amount or mask!");
	}
	const C = ge_double_scalarmult_base_vartime(amount, H, mask);
	return C;
}

export function zeroCommit(amount: string) {
	return commit(amount, I);
}

export function decode_ecdh(ecdh: Commit, key: string): Commit {
	const first = hash_to_scalar(key);
	const second = hash_to_scalar(first);
	return {
		mask: sc_sub(ecdh.mask, first),
		amount: sc_sub(ecdh.amount, second),
	};
}

export function encode_ecdh(ecdh: Commit, key: string): Commit {
	const first = hash_to_scalar(key);
	const second = hash_to_scalar(first);
	return {
		mask: sc_add(ecdh.mask, first),
		amount: sc_add(ecdh.amount, second),
	};
}

export async function generate_key_image_helper(
	keys: Keys,
	tx_pub_key: string,
	out_index: number,
	enc_mask: string | null | undefined,
	hwdev: HWDevice,
) {
	const recv_derivation = await hwdev.generate_key_derivation(
		tx_pub_key,
		keys.view.sec,
	);
	if (!recv_derivation) throw Error("Failed to generate key image");
	const maskFunc = (derivation: string) =>
		enc_mask
			? sc_sub(
					enc_mask,
					hash_to_scalar(derivation_to_scalar(derivation, out_index)),
			  )
			: I; //decode mask, or d2s(1) if no mask

	let mask: string = "";
	// wallet2::light_wallet_parse_rct_str

	if (hwdev instanceof LedgerDevice) {
		const privViewKey = await hwdev.export_private_view_key();
		const derivation = generate_key_derivation(tx_pub_key, privViewKey);
		mask = maskFunc(derivation);
	} else {
		mask = maskFunc(recv_derivation);
	}

	const ephemeral_sec = await hwdev.derive_secret_key(
		recv_derivation,
		out_index,
		keys.spend.sec,
	);

	const ephemeral_pub = await hwdev.secret_key_to_public_key(ephemeral_sec);
	if (!ephemeral_pub) throw Error("Failed to generate key image");

	const key_image = await hwdev.generate_key_image(
		ephemeral_pub,
		ephemeral_sec,
	);

	return {
		in_ephemeral: {
			pub: ephemeral_pub,
			sec: ephemeral_sec,
			mask,
		},
		key_image,
	};
}

export function scalarmultH(scalar: string) {
	return ge_scalarmult(H, scalar);
}