/**
 * Triple DES implementation used internally for PDF encryption.
 *
 * @private
 */
export declare class _TripleDataEncryptionStandardCipher {
    /**
     * Block size in bytes (DES block size).
     *
     * @private
     */
    readonly _blockSize: number;
    private _key1;
    private _key2;
    private _key3;
    private _isEncryption;
    /**
     * S-box 1 table.
     *
     * @private
     */
    _sp1: number[];
    /**
     * S-box 2 table.
     *
     * @private
     */
    _sp2: number[];
    /**
     * S-box 3 table.
     *
     * @private
     */
    _sp3: number[];
    /**
     * S-box 4 table.
     *
     * @private
     */
    _sp4: number[];
    /**
     * S-box 5 table.
     *
     * @private
     */
    _sp5: number[];
    /**
     * S-box 6 table.
     *
     * @private
     */
    _sp6: number[];
    /**
     * S-box 7 table.
     *
     * @private
     */
    _sp7: number[];
    /**
     * S-box 8 table.
     *
     * @private
     */
    _sp8: number[];
    /**
     * Create a Triple DES cipher instance with the given key.
     *
     * @private
     * @param {Uint8Array} key - The 16- or 24-byte Triple DES key.
     * @param {boolean} isEncryption - Whether the cipher will be used for encryption.
     */
    constructor(key: Uint8Array, isEncryption?: boolean);
    /**
     * Read a big-endian unsigned 32-bit integer from a byte array.
     *
     * @private
     * @param {Uint8Array} b - Source byte array.
     * @param {number} off - Byte offset to read from.
     * @returns {number} The 32-bit unsigned integer value.
     */
    _beToUint32(b: Uint8Array, off: number): number;
    /**
     * Write a 32-bit unsigned integer to a byte array in big-endian order.
     *
     * @private
     * @param {number} v - Value to write.
     * @param {Uint8Array} b - Destination byte array.
     * @param {number} off - Byte offset to write to.
     * @returns {void}
     */
    _uint32ToBe(v: number, b: Uint8Array, off: number): void;
    /**
     * Generate the DES round keys (working key) from the provided key bytes.
     *
     * @private
     * @param {boolean} isEncrypt - Whether the keys are for encryption (true) or decryption (false).
     * @param {Uint8Array} keyBytes - The 8-byte key material.
     * @returns {Int32Array} An `Int32Array` representing round subkeys.
     */
    _generateWorkingKey(isEncrypt: boolean, keyBytes: Uint8Array): Int32Array;
    /**
     * Process a single DES round using the supplied subkeys.
     *
     * @private
     * @param {Int32Array} keys - Round subkeys to use.
     * @param {Uint8Array} inBytes - Input byte array.
     * @param {number} inOffset - Offset into input array.
     * @param {Uint8Array} outBytes - Output byte array.
     * @param {number} outOffset - Offset into output array.
     * @returns {void}
     */
    _processEncryptionBlock(keys: Int32Array, inBytes: Uint8Array, inOffset: number, outBytes: Uint8Array, outOffset: number): void;
    /**
     * Process a Triple DES block.
     *
     * @private
     * @param {Uint8Array} input - Input bytes containing the block.
     * @param {number} inOffset - Offset into `input` where the block starts.
     * @param {Uint8Array} output - Destination byte array.
     * @param {number} outOffset - Offset into `output` to write the block.
     * @returns {number} The block size in bytes.
     */
    _processBlock(input: Uint8Array, inOffset: number, output: Uint8Array, outOffset: number): number;
}