/**
 * Encodes the string as UTF-8 bytes. The plain implementation is used on purpose.
 * It does not depend on `TextEncoder` or `Buffer`, so the same code works in
 * Node.js and in every browser, including plain http:// pages.
 *
 * @param {string} string The string to encode.
 * @returns {number[]}
 */
export declare function stringToUtf8Bytes(string: string): number[];
/**
 * Decodes UTF-8 bytes back into a string.
 *
 * @param {number[]} bytes The bytes to decode.
 * @returns {string}
 */
export declare function utf8BytesToString(bytes: number[]): string;
/**
 * Encodes the bytes as a base64 string (standard alphabet, with padding).
 *
 * @param {number[]} bytes The bytes to encode.
 * @returns {string}
 */
export declare function bytesToBase64(bytes: number[]): string;
/**
 * Decodes a base64 string (standard or URL-safe alphabet, padding optional)
 * back into bytes. Returns `null` when the string is not valid base64.
 *
 * @param {string} base64 The base64 string to decode.
 * @returns {number[]|null}
 */
export declare function base64ToBytes(base64: string): number[] | null;
/**
 * Encodes the string as a URL-safe base64 string without padding (the same
 * format as the JWT payload segment).
 *
 * @param {string} string The string to encode.
 * @returns {string}
 */
export declare function stringToBase64Url(string: string): string;
/**
 * Decodes a base64 (standard or URL-safe) string back into a string.
 * Returns `null` when the input is not valid base64.
 *
 * @param {string} base64 The base64 string to decode.
 * @returns {string|null}
 */
export declare function base64ToString(base64: string): string | null;
/**
 * Parses a date in the "YYYY-MM-DD" format into the epoch milliseconds of its
 * UTC midnight. Returns `null` when the date is malformed or does not exist in
 * the calendar (for example "2027-02-30"). Unlike the generator side, the
 * reader never throws on a bad date - a broken payload simply makes the key
 * unreadable.
 *
 * @param {string} isoDate The date to parse.
 * @returns {number|null}
 */
export declare function parseIsoDateToTimestamp(isoDate: unknown): number | null;