@gandlaf21/cashu-crypto/src/common/index.ts

Basic cashu crypto functions

import { ProjPointType } from '@noble/curves/abstract/weierstrass';
import { secp256k1 } from '@noble/curves/secp256k1';
import { sha256 } from '@noble/hashes/sha256';
import { bytesToHex, hexToBytes } from '@noble/curves/abstract/utils';
import { bytesToNumber, encodeBase64toUint8, hexToNumber } from '../util/utils.js';

export type Enumerate<N extends number, Acc extends number[] = []> = Acc['length'] extends N
	? Acc[number]
	: Enumerate<N, [...Acc, Acc['length']]>;

export type IntRange<F extends number, T extends number> = Exclude<Enumerate<T>, Enumerate<F>>;

export type MintKeys = { [k: string]: Uint8Array };

export type SerializedMintKeys = {
	[k: string]: string;
};

export type Keyset = {
	id: string;
	unit: string;
	active: boolean;
};

export type BlindSignature = {
	C_: ProjPointType<bigint>;
	amount: number;
	id: string;
};

export type SerializedBlindSignature = {
	C_: string;
	amount: number;
	id: string;
};

export type Proof = {
	C: ProjPointType<bigint>;
	secret: Uint8Array;
	amount: number;
	id: string;
	witness?: Witness;
};

export type SerializedProof = {
	C: string;
	secret: string;
	amount: number;
	id: string;
	witness?: string;
};

export type SerializedBlindedMessage = {
	B_: string;
	amount: number;
	witness?: string;
};

export type Secret = [WellKnownSecret, SecretData];

export type WellKnownSecret = 'P2PK';

export type SecretData = {
	nonce: string;
	data: string;
	tags?: Array<Array<string>>;
};

export type Witness = {
	signatures: Array<string>;
};

export type Tags = {
	[k: string]: string;
};

export type SigFlag = 'SIG_INPUTS' | 'SIG_ALL';

const DOMAIN_SEPARATOR = hexToBytes('536563703235366b315f48617368546f43757276655f43617368755f');

export function hashToCurve(secret: Uint8Array): ProjPointType<bigint> {
	const msgToHash = sha256(Buffer.concat([DOMAIN_SEPARATOR, secret]));
	const counter = new Uint32Array(1);
	const maxIterations = 2 ** 16;
	for (let i = 0; i < maxIterations; i++) {
		const counterBytes = new Uint8Array(counter.buffer);
		const hash = sha256(Buffer.concat([msgToHash, counterBytes]));
		try {
			return pointFromHex(bytesToHex(Buffer.concat([new Uint8Array([0x02]), hash])));
		} catch (error) {
			counter[0]++;
		}
	}
	throw new Error('No valid point found');
}

export function pointFromHex(hex: string) {
	return secp256k1.ProjectivePoint.fromHex(hex);
}

export const getKeysetIdInt = (keysetId: string): bigint => {
	let keysetIdInt: bigint;
	if (/^[a-fA-F0-9]+$/.test(keysetId)) {
		keysetIdInt = hexToNumber(keysetId) % BigInt(2 ** 31 - 1);
	} else {
		//legacy keyset compatibility
		keysetIdInt = bytesToNumber(encodeBase64toUint8(keysetId)) % BigInt(2 ** 31 - 1);
	}
	return keysetIdInt;
};

export function createRandomPrivateKey() {
	return secp256k1.utils.randomPrivateKey();
}

export function serializeMintKeys(mintKeys: MintKeys): SerializedMintKeys {
	const serializedMintKeys: SerializedMintKeys = {};
	Object.keys(mintKeys).forEach((p) => {
		serializedMintKeys[p] = bytesToHex(mintKeys[p]);
	});
	return serializedMintKeys;
}

export function deserializeMintKeys(serializedMintKeys: SerializedMintKeys): MintKeys {
	const mintKeys: MintKeys = {};
	Object.keys(serializedMintKeys).forEach((p) => {
		mintKeys[p] = hexToBytes(serializedMintKeys[p]);
	});
	return mintKeys;
}

export function deriveKeysetId(keys: MintKeys): string {
	const KEYSET_VERSION = '00';
	const mapBigInt = (k: [string, string]): [bigint, string] => {
		return [BigInt(k[0]), k[1]];
	};
	const pubkeysConcat = Object.entries(serializeMintKeys(keys))
		.map(mapBigInt)
		.sort((a, b) => (a[0] < b[0] ? -1 : a[0] > b[0] ? 1 : 0))
		.map(([, pubKey]) => hexToBytes(pubKey)).reduce((prev,curr)=>mergeUInt8Arrays(prev,curr),new Uint8Array())
	const hash = sha256(pubkeysConcat);
	const hashHex =  Buffer.from(hash).toString('hex').slice(0, 14)
	return '00' + hashHex
}

function mergeUInt8Arrays(a1: Uint8Array, a2: Uint8Array): Uint8Array {
	// sum of individual array lengths
	const mergedArray = new Uint8Array(a1.length + a2.length);
	mergedArray.set(a1);
	mergedArray.set(a2, a1.length);
	return mergedArray;
  }