/**
 * * Generates a random hexadecimal string of the specified length.
 *
 * @param length - Number of hex characters to generate.
 * @param uppercase - Whether to return uppercase `A–F` characters. Defaults to `false` (lowercase).
 *
 * @returns A randomly generated hexadecimal string.
 *
 * @remarks
 * - This function generates a random hexadecimal string of the specified length.
 * - It uses {@link crypto.getRandomValues} when available for secure randomness, and falls back to {@link Math.random} if not.
 * - The output is a string of hex characters (`0–9`, `a–f` or `A–F`) with no prefixes or separators.
 * - If `length` is `0` or negative, an empty string is returned.
 *
 * @example
 * // 16-character lowercase hex
 * const id = randomHex(16);
 *
 * @example
 * // 8-character uppercase hex
 * const token = randomHex(8, true);
 */
export declare function randomHex(length: number, uppercase?: boolean): string;
/**
 * * Converts a UTF-8 string to a byte array (`Uint8Array`).
 *
 * This function encodes a JavaScript string into UTF-8 bytes, handling all Unicode code points including supplementary characters (surrogate pairs).
 *
 * @example
 * ```typescript
 * // Basic ASCII
 * const asciiBytes = utf8ToBytes('hello');
 * // Returns:
 * Uint8Array(5) [104, 101, 108, 108, 111]
 *
 * // Unicode characters
 * const unicodeBytes = utf8ToBytes('Hello পৃথিবী!');
 * // Returns:
 * Uint8Array(25) [
 *  72, 101, 108, 108, 111,  32,
 * 224, 166, 170, 224, 167, 131,
 * 224, 166, 165, 224, 166, 191,
 * 224, 166, 172, 224, 167, 128,
 *  33
 * ]
 * ```
 *
 * @param str - The input string to encode as UTF-8 bytes.
 * @returns A `Uint8Array` containing the UTF-8 encoded bytes.
 *
 * @remarks
 * - The encoding follows the UTF-8 specification:
 *   - 1-byte sequence for code points U+0000 to U+007F (ASCII)
 *   - 2-byte sequence for code points U+0080 to U+07FF
 *   - 3-byte sequence for code points U+0800 to U+FFFF
 *   - 4-byte sequence for code points U+10000 to U+10FFFF (surrogate pairs)
 *
 * **Note:** Invalid surrogate pairs in the input string are silently ignored.
 *
 * @see {@link bytesToUtf8} for the inverse operation
 */
export declare function utf8ToBytes(str: string): Uint8Array;
/**
 * * Converts `UTF-8` encoded bytes back to a string.
 *
 * This function decodes a `Uint8Array` containing `UTF-8` bytes into a JavaScript string.
 *
 * @example
 * ```typescript
 * // Decode UTF-8 bytes
 * const bytes = new Uint8Array([104, 101, 108, 108, 111]);
 * const str = bytesToUtf8(bytes);
 * // Returns: 'hello'
 *
 * // Round-trip conversion
 * const original = 'Hello 🌍';
 * const bytes = utf8ToBytes(original);
 * const decoded = bytesToUtf8(bytes);
 * console.log(original === decoded); // true
 * ```
 *
 * @param bytes - A `Uint8Array` containing `UTF-8` encoded bytes.
 * @returns The decoded string.
 *
 * @remarks
 * - The function handles all valid `UTF-8` sequences:
 *   - 1-byte sequences (0xxxxxxx) → ASCII characters
 *   - 2-byte sequences (110xxxxx 10xxxxxx)
 *   - 3-byte sequences (1110xxxx 10xxxxxx 10xxxxxx)
 *   - 4-byte sequences (11110xxx 10xxxxxx 10xxxxxx 10xxxxxx) → surrogate pairs
 *
 * @see {@link utf8ToBytes} for the inverse operation
 */
export declare function bytesToUtf8(bytes: Uint8Array): string;
/**
 * * Decodes a `Base64` string to bytes.
 *   - This function converts a `Base64`-encoded string back to its original byte representation.
 *   - It handles standard `Base64` encoding with '=', '+', '/' characters.
 *
 * @example
 * ```typescript
 * // Decode Base64 string
 * const bytes = base64ToBytes('aGVsbG8gd29ybGQ=');
 * // Returns: Uint8Array(11) [104, 101, 108, 108, 111, 32, 119, 111, 114, 108, 100]
 *
 * // Empty string
 * const empty = base64ToBytes('');
 * // Returns: Uint8Array(0) []
 * ```
 *
 * @param str - The `Base64`-encoded string to decode.
 * @returns A `Uint8Array` containing the decoded bytes.
 *
 * @remarks
 * - The function supports:
 *   - Standard `Base64` alphabet (A-Z, a-z, 0-9, +, /)
 *   - Padding with '=' characters
 *   - Ignores whitespace (though not explicitly trimmed in this implementation)
 *
 * @see {@link bytesToBase64} for the inverse operation
 */
export declare function base64ToBytes(str: string): Uint8Array;
/**
 * * Encodes bytes to a `Base64` string.
 *   - This function converts a `Uint8Array` to a `Base64`-encoded string using the standard `Base64` alphabet with padding.
 *
 * @example
 * ```typescript
 * // Encode bytes to Base64
 * const bytes = new Uint8Array([104, 101, 108, 108, 111, 32, 119, 111, 114, 108, 100]);
 * const b64 = bytesToBase64(bytes);
 * // Returns: 'aGVsbG8gd29ybGQ='
 *
 * // Empty array
 * const empty = bytesToBase64(new Uint8Array(0));
 * // Returns: ''
 * ```
 *
 * @param bytes - The bytes to encode as `Base64`.
 * @returns The `Base64`-encoded string.
 *
 * @remarks
 * The encoding uses:
 * - Standard `Base64` alphabet (A-Z, a-z, 0-9, +, /)
 * - '=' padding for incomplete groups
 * - No line breaks or whitespace
 *
 * This is a pure JavaScript implementation that doesn't rely on `btoa()`.
 *
 * @see {@link base64ToBytes} for the inverse operation
 */
export declare function bytesToBase64(bytes: Uint8Array): string;
/**
 * * Concatenates multiple `Uint8Array`s into a single `Uint8Array`.
 *   - This function efficiently combines multiple byte arrays without creating intermediate strings or arrays.
 *
 * @example
 * ```typescript
 * // Concatenate multiple arrays
 * const a = new Uint8Array([1, 2, 3]);
 * const b = new Uint8Array([4, 5]);
 * const c = new Uint8Array([6, 7, 8, 9]);
 * const result = concatBytes(a, b, c);
 * // Returns: Uint8Array(9) [1, 2, 3, 4, 5, 6, 7, 8, 9]
 *
 * // Single array
 * const single = concatBytes(new Uint8Array([1, 2, 3]));
 * // Returns: Uint8Array(3) [1, 2, 3]
 *
 * // No arrays
 * const empty = concatBytes();
 * // Returns: Uint8Array(0) []
 * ```
 *
 * @param parts - One or more `Uint8Array`s to concatenate.
 * @returns A new `Uint8Array` containing all the bytes from the input arrays in the order they were provided.
 *
 * @remarks The function allocates a single `Uint8Array` of the total combined length and copies all bytes into it using `set()` for optimal performance.
 */
export declare function concatBytes(...parts: Uint8Array[]): Uint8Array;
/**
 * * Computes the `SHA-256` hash of raw bytes.
 *   - This is a pure JavaScript implementation of the `SHA-256` cryptographic hash function that operates directly on byte arrays (`Uint8Array`).
 *
 * @example
 * ```typescript
 * // Hash raw bytes
 * const bytes = new Uint8Array([104, 101, 108, 108, 111]); // "hello"
 * const hash = sha256Bytes(bytes);
 * // Returns: Uint8Array(32) with SHA-256 hash
 *
 * // Verify with string hash
 * const strHash = sha256('hello');
 * const bytesHash = bytesToHex(sha256Bytes(utf8ToBytes('hello')));
 * console.log(strHash === bytesHash); // true
 * ```
 *
 * @param message - The bytes to hash as a `Uint8Array`.
 * @returns A `Uint8Array` of 32 bytes (256 bits) containing the `SHA-256` hash.
 *
 * @remarks
 * - Implementation details:
 *   - Follows the `SHA-256` specification (FIPS 180-4)
 *   - Uses big-endian byte order throughout
 *   - Processes messages in 512-bit (64-byte) blocks
 *   - Applies proper padding with message length
 *   - Uses all required `SHA-256` round constants
 *   - Returns hash as 32-byte array
 *
 * @see {@link hmacSha256} for `HMAC-SHA256` computation
 */
export declare function sha256Bytes(message: Uint8Array): Uint8Array;
/**
 * * Computes `HMAC-SHA256` (Hash-based Message Authentication Code using `SHA-256`).
 *  - This function implements the `HMAC` algorithm with `SHA-256` as the underlying hash function, providing message authentication and integrity verification.
 *
 * @example
 * ```typescript
 * // Basic HMAC calculation
 * const key = new TextEncoder().encode('secret-key');
 * const message = new TextEncoder().encode('Hello, world!');
 * const hmac = hmacSha256(key, message);
 *
 * // Using with string inputs
 * const keyBytes = new TextEncoder().encode('my-key');
 * const msgBytes = new TextEncoder().encode('data to authenticate');
 * const hmacResult = hmacSha256(keyBytes, msgBytes);
 * const hexResult = bytesToHex(hmacResult);
 * ```
 *
 * @param key - The secret key as a `Uint8Array`.
 * @param message - The message to authenticate as a `Uint8Array`.
 * @returns A `Uint8Array` of 32 bytes containing the `HMAC-SHA256` tag.
 *
 * @remarks
 * - Algorithm steps:
 *   - 1. Keys longer than 64 bytes are hashed with `SHA-256`
 *   - 2. Keys shorter than 64 bytes are padded with zeros
 *   - 3. Inner hash: `SHA-256((key ⊕ ipad) || message)` where ipad = 0x36 repeated
 *   - 4. Outer hash: `SHA-256((key ⊕ opad) || inner_hash)` where opad = 0x5C repeated
 *
 * - The implementation follows RFC 2104 and RFC 4231 specifications.
 * - Block size for `SHA-256` HMAC is 64 bytes (512 bits).
 *
 * **Common use cases:**
 * - API authentication tokens
 * - Message integrity verification
 * - Key derivation (as part of `HKDF`)
 *
 * @see {@link sha256Bytes} for the underlying hash function
 */
export declare function hmacSha256(key: Uint8Array, message: Uint8Array): Uint8Array;
/**
 * * Converts a `Uint8Array` to a `Uint32Array` with big-endian byte order.
 *   - This function groups bytes into 32-bit integers, reading them in big-endian (most significant byte first) order. Missing bytes are treated as zero.
 *
 * @example
 * ```typescript
 * // Convert bytes to 32-bit integers
 * const bytes = new Uint8Array([0x12, 0x34, 0x56, 0x78, 0x9A, 0xBC]);
 * const words = uint8To32ArrayBE(bytes);
 * // Returns: Uint32Array(2) [0x12345678, 0x9ABC0000] or equivalent: Uint32Array(2) [ 305419896, 2596012032 ]
 *
 * // Partial final word
 * const partial = new Uint8Array([0xFF, 0xEE, 0xDD]);
 * const words2 = uint8To32ArrayBE(partial);
 * // Returns: Uint32Array(1) [0xFFEEDD00] or equivalent: Uint32Array(1) [ 4293844224 ]
 * ```
 *
 * @param bytes - The bytes to convert to 32-bit words.
 * @returns A `Uint32Array` containing the 32-bit big-endian words.
 *
 * @remarks
 * - Input length doesn't need to be a multiple of 4
 * - Missing bytes in the final word are padded with zeros
 * - Byte order: `bytes[0]` is the most significant byte of `out[0]`
 * - This is useful for cryptographic operations that work with 32-bit words
 */
export declare function uint8To32ArrayBE(bytes: Uint8Array): Uint32Array;
/**
 * * Converts a 32-bit integer into a 4-byte `Uint8Array` in big-endian (network) byte order.
 *   - This function takes a 32-bit integer and encodes it as 4 bytes with the most significant byte first (big-endian order), which is the standard for network protocols and many cryptographic operations.
 *
 * @example
 * ```typescript
 * // Convert integer to bytes
 * const bytes = intTo4BytesBE(0x12345678);
 * // Returns: Uint8Array(4) [0x12, 0x34, 0x56, 0x78] or equivalent: Uint8Array(4) [ 18, 52, 86, 120 ]
 *
 * // Maximum 32-bit value
 * const maxBytes = intTo4BytesBE(0xFFFFFFFF);
 * // Returns: Uint8Array(4) [0xFF, 0xFF, 0xFF, 0xFF]
 *
 * // Zero
 * const zeroBytes = intTo4BytesBE(0);
 * // Returns: Uint8Array(4) [0x00, 0x00, 0x00, 0x00]
 * ```
 *
 * @param n - The 32-bit integer to convert. Values beyond 32 bits will be truncated.
 * @returns A 4-byte `Uint8Array` representing the value in big-endian format.
 *
 * @remarks
 * - The function uses unsigned 32-bit arithmetic (`>>>` operator)
 * - Only the lower 32 bits of the input are used (truncation)
 * - Output is always exactly 4 bytes
 * - Big-endian order: byte[0] = most significant, byte[3] = least significant
 *
 * **Common use cases:**
 * - Encoding message lengths in network protocols
 * - Preparing data for cryptographic operations
 * - Converting integers for storage or transmission
 *
 * @see {@link uint8To32ArrayBE} for bytes to 32-bit integers conversion
 */
export declare function intTo4BytesBE(n: number): Uint8Array;
/**
 * * Converts a `Uint8Array` to a lowercase hexadecimal string.
 *   - This function encodes binary data (bytes) as a hexadecimal string, with each byte represented as two lowercase hexadecimal digits (0-9, a-f).
 *
 * @example
 * ```typescript
 * // Convert bytes to hex
 * const bytes = new Uint8Array([0x12, 0xAB, 0xFF, 0x00]);
 * const hex = bytesToHex(bytes);
 * // Returns: '12abff00'
 *
 * // Empty array
 * const emptyHex = bytesToHex(new Uint8Array(0));
 * // Returns: ''
 *
 * // SHA-256 hash to hex
 * const hashBytes = sha256Bytes(utf8ToBytes('hello'));
 * const hashHex = bytesToHex(hashBytes);
 * // Returns: '2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824'
 * ```
 *
 * @param bytes - The bytes to convert to hexadecimal representation.
 * @returns A lowercase hexadecimal string where each byte is represented by two characters (00-ff).
 *
 * @remarks
 * - Always returns lowercase letters (a-f)
 * - Zero pads single-digit hex values (e.g., 0x0F → "0f", not "f")
 * - Efficient O(n) implementation using string concatenation
 * - No prefix (e.g., no "0x" at the beginning)
 *
 * **Common use cases:**
 * - Displaying cryptographic hashes and signatures
 * - Debugging binary data
 * - Converting binary data for JSON serialization
 * - Creating hex-encoded strings for APIs and protocols
 *
 * @see {@link hexToBytes} for reverse process
 */
export declare function bytesToHex(bytes: Uint8Array): string;
/**
 * * Converts a hexadecimal string to a `Uint8Array`.
 *   - This function decodes a hexadecimal-encoded string into its raw byte representation, where every two hexadecimal characters (00–ff) are converted into one byte.
 *
 * @example
 * // Convert hex to bytes
 * const hex = '12abff00';
 * const bytes = hexToBytes(hex);
 * // Returns: Uint8Array(4) [18, 171, 255, 0]
 *
 * // Empty string
 * const emptyBytes = hexToBytes('');
 * // Returns: Uint8Array []
 *
 * // Decode SHA-256 hash from hex
 * const hashHex = '2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824';
 * const hashBytes = hexToBytes(hashHex);
 * // Returns: Uint8Array(32)
 *
 * @param hex - A hexadecimal string where each byte is represented by two characters (00–ff).
 * @returns A `Uint8Array` containing the decoded bytes. Returns an empty array for invalid input.
 *
 * @remarks
 * - Accepts lowercase and uppercase hexadecimal characters (0–9, a–f, A–F) with or without space between bytes
 * - Ignores no prefixes (e.g., does not support "0x")
 * - Requires an even number of hexadecimal characters
 * - Efficient O(n) implementation with direct byte parsing
 *
 * **Common use cases:**
 * - Decoding cryptographic hashes and signatures
 * - Parsing hex-encoded binary payloads
 * - Reconstructing binary data from storage or transport formats
 * - Working with low-level protocols and binary APIs
 *
 * @see {@link bytesToHex} for the reverse process
 */
export declare function hexToBytes(hex: string): Uint8Array;