import { _PdfNativeAccumulatorSink, _PdfNativeHashInput } from '../digital-signature/signature/pdf-accumulator';
/**
 * SHA-256 hash implementation used internally for PDF cryptography.
 *
 * @private
 */
export declare class _Sha256 {
    /**
     * Create a chunked conversion sink for incremental hashing.
     *
     * @private
     * @param {_PdfNativeAccumulatorSink} outputSink - Sink that will receive the hash output.
     * @returns {_PdfNativeHashInput} A `_PdfNativeHashInput` for feeding chunks.
     */
    _startChunkedConversion(outputSink: _PdfNativeAccumulatorSink): _PdfNativeHashInput;
    /**
     * Rotate a 32 bit value right by `n` bits.
     *
     * @private
     * @param {number} x - The 32 bit value to rotate.
     * @param {number} n - The number of bits to rotate.
     * @returns {number} The rotated 32-bit value.
     */
    _rotateRight(x: number, n: number): number;
    /**
     * Upper case sigma function used in SHA-256.
     *
     * @private
     * @param {number} x - The input 32-bit word.
     * @returns {number} The transformed 32-bit word.
     */
    _sigma(x: number): number;
    /**
     * Upper-case sigma prime function used in SHA-256.
     *
     * @private
     * @param {number} x - The input 32-bit word.
     * @returns {number} The transformed 32-bit word.
     */
    _sigmaPrime(x: number): number;
    /**
     * Lower-case sigma function used in the message schedule.
     *
     * @private
     * @param {number} x - The input 32-bit word.
     * @returns {number} The transformed 32-bit word.
     */
    _littleSigma(x: number): number;
    /**
     * Lower-case sigma prime function used in the message schedule.
     *
     * @private
     * @param {number} x The input 32-bit word.
     * @returns {number} The transformed 32-bit word.
     */
    _littleSigmaPrime(x: number): number;
    /**
     * Compute the SHA-256 hash for a slice of bytes.
     *
     * @private
     * @param {Uint8Array} data bytes.
     * @param {number}  offset into `data`.
     * @param {number} length of bytes to hash.
     * @returns {Uint8Array} The 32-byte SHA-256 digest as `Uint8Array`.
     */
    _hash(data: Uint8Array, offset: number, length: number): Uint8Array;
}