/**
 *
 * @param {Uint8Array} key
 * @param {Uint8Array} nonce
 * @param {number} counter
 * @throws {Error}
 *
 * @constructor
 */
export declare class Chacha20 {
    readonly key: Uint8Array;
    readonly nonce: Uint8Array;
    readonly counter?: number;
    _rounds: number;
    _sigma: number[];
    _param: number[];
    _keystream: number[];
    constructor(key: Uint8Array, nonce: Uint8Array, counter?: number);
    _byteCounter: number;
    _chacha(): void;
    /**
     * The basic operation of the ChaCha algorithm is the quarter round.
     * It operates on four 32-bit unsigned integers, denoted a, b, c, and d.
     *
     * @param {Array} output
     * @param {number} a
     * @param {number} b
     * @param {number} c
     * @param {number} d
     * @private
     */
    private _quarterround;
    /**
     * Little-endian to uint 32 bytes
     *
     * @param {Uint8Array|[number]} data
     * @param {number} index
     * @return {number}
     * @private
     */
    private _get32;
    /**
     * Cyclic left rotation
     *
     * @param {number} data
     * @param {number} shift
     * @return {number}
     * @private
     */
    private _rotl;
    /**
     *  Encrypt data with key and nonce
     *
     * @param {Uint8Array} data
     * @return {Uint8Array}
     */
    encrypt(data: Uint8Array): Uint8Array;
    /**
     *  Decrypt data with key and nonce
     *
     * @param {Uint8Array} data
     * @return {Uint8Array}
     */
    decrypt(data: Uint8Array): Uint8Array;
    /**
     *  Encrypt or Decrypt data with key and nonce
     *
     * @param {Uint8Array} data
     * @return {Uint8Array}
     * @private
     */
    private _update;
}