import { _ICipherParam } from './pdf-interfaces';
/**
 * Provides internal utilities for performing hash selection, key validation,
 * and RSA-based signing operations using supported digest algorithms.
 *
 * @private
 */
export declare class _PdfSignaturePrivateKey {
    private _key;
    private _hashAlgorithm;
    private _encryptionAlgorithm;
    constructor(hashAlgorithm: string, key?: _ICipherParam);
    /**
     * Determines whether the provided key is a valid RSA (Ron cipher) private key.
     *
     * @private
     * @param {_ICipherParam} key The key to inspect for RSA-compatible fields.
     * @returns {boolean} True if the key includes both 'modulus' and 'privateExponent'; otherwise, false.
     */
    _isRonCipherKey(key: _ICipherParam): boolean;
    /**
     * Generates a digital signature for the given byte data using the selected
     * digest and RSA encryption algorithm.
     *
     * @private
     * @param {Uint8Array} bytes The input byte sequence to sign.
     * @returns {Uint8Array} The generated signature, or null if an error occurs.
     */
    _sign(bytes: Uint8Array): Uint8Array;
    /**
     * Gets the internal hash algorithm associated with this signing key.
     *
     * @private
     * @returns {string} The normalized hash algorithm name (e.g., "SHA1", "SHA256").
     */
    _getHashAlgorithm(): string;
    /**
     * Gets the internal encryption algorithm used for signature generation.
     *
     * @private
     * @returns {string} The encryption algorithm name (e.g., "RSA").
     */
    _getEncryptionAlgorithm(): string;
}