bip322-js/dist/helpers/Key.js

A Javascript library that provides utility functions related to the BIP-322 signature scheme

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
const elliptic_1 = require("elliptic");
/**
 * Class that implement key-related utility functions.
 */
class Key {
    /**
     * Converts a 33-byte Bitcoin public key to a 32-byte x-only public key as used in Taproot.
     * This function checks if the provided public key buffer is already 32 bytes long,
     * in which case it returns the buffer unchanged. If the buffer is 33 bytes long, it
     * assumes that the first byte is the parity byte used for indicating the y-coordinate
     * in traditional SEC1 encoding and removes this byte, thereby converting the public key
     * to an x-only format suitable for use with Bitcoin's Taproot.
     *
     * Adopted from https://github.com/ACken2/bip322-js/pull/6 by Czino
     *
     * @param publicKey The buffer containing the 33-byte or 32-byte public key to be converted.
     * @returns A 32-byte buffer of the x-only public key.
     * @throws If the public key is neither 32-byte nor 33-byte long
     */
    static toXOnly(publicKey) {
        // Throw if the input key length is invalid
        if (publicKey.length !== 32 && publicKey.length !== 33) {
            throw new Error("Invalid public key length");
        }
        // Otherwise, return the key (with the first byte removed if it is 33-byte long)
        return Buffer.from(publicKey.length === 32 ? publicKey : publicKey.subarray(1, 33));
    }
    /**
     * Compresses an uncompressed public key using the elliptic curve secp256k1.
     * This method takes a public key in its uncompressed form and returns a compressed
     * representation of the public key. Elliptic curve public keys can be represented in
     * a shorter form known as compressed format which saves space and still retains the
     * full public key's capabilities. The method uses the elliptic library to convert the
     * uncompressed public key into its compressed form.
     *
     * The steps involved in the process are:
     * 1. Initialize a new elliptic curve instance for the secp256k1 curve.
     * 2. Create a key pair object from the uncompressed public key buffer.
     * 3. Extract the compressed public key from the key pair object.
     * 4. Return the compressed public key as a Buffer object.
     *
     * @param uncompressedPublicKey A Buffer containing the uncompressed public key.
     * @return Buffer Returns a Buffer containing the compressed public key.
     * @throws Error Throws an error if the provided public key cannot be compressed,
     *         typically indicating that the key is not valid.
     */
    static compressPublicKey(uncompressedPublicKey) {
        // Initialize elliptic curve
        const ec = new elliptic_1.ec('secp256k1');
        // Try to compress the provided public key
        try {
            // Create a key pair from the uncompressed public key buffer
            const keyPair = ec.keyFromPublic(Buffer.from(uncompressedPublicKey));
            // Get the compressed public key as a Buffer
            const compressedPublicKey = Buffer.from(keyPair.getPublic(true, 'array'));
            return compressedPublicKey;
        }
        catch (err) {
            throw new Error('Fails to compress the provided public key. Please check if the provided key is a valid uncompressed public key.');
        }
    }
    /**
     * Uncompresses a given public key using the elliptic curve secp256k1.
     * This method accepts a compressed public key and attempts to convert it into its
     * uncompressed form. Public keys are often compressed to save space, but certain
     * operations require the full uncompressed key. This method uses the elliptic
     * library to perform the conversion.
     *
     * The function operates as follows:
     * 1. Initialize a new elliptic curve instance using secp256k1.
     * 2. Attempt to create a key pair from the compressed public key buffer.
     * 3. Extract the uncompressed public key from the key pair object.
     * 4. Return the uncompressed public key as a Buffer object.
     * If the compressed public key provided is invalid and cannot be uncompressed,
     * the method will throw an error with a descriptive message.
     *
     * @param compressedPublicKey A Buffer containing the compressed public key.
     * @return Buffer The uncompressed public key as a Buffer.
     * @throws Error Throws an error if the provided public key cannot be uncompressed,
     *         typically indicating that the key is not valid.
     */
    static uncompressPublicKey(compressedPublicKey) {
        // Initialize elliptic curve
        const ec = new elliptic_1.ec('secp256k1');
        // Try to uncompress the provided public key
        try {
            // Create a key pair from the compressed public key buffer
            const keyPair = ec.keyFromPublic(Buffer.from(compressedPublicKey));
            // Get the compressed public key as a Buffer
            const uncompressedPublicKey = Buffer.from(keyPair.getPublic(false, 'array'));
            return uncompressedPublicKey;
        }
        catch (err) {
            throw new Error('Fails to uncompress the provided public key. Please check if the provided key is a valid compressed public key.');
        }
    }
}
exports.default = Key;
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