/// <reference types="node" />
import { SecurityKey } from '../key';
/**
 * SecurityKeyPrivate constructor.
 */
export declare abstract class SecurityKeyPrivate extends SecurityKey {
    constructor();
    /**
     * Sign data.
     *
     * @param data Data to be signed.
     * @param digest Digest algorithm.
     * @returns The signature.
     */
    abstract sign(data: Readonly<Buffer>, digest: string): Buffer;
}