/**
 * Constant-time byte comparison for cryptographic signatures.
 * Never short-circuits the XOR loop; length mismatch is folded into `diff`.
 */
export declare function timingSafeEqual(a: Uint8Array, b: Uint8Array): boolean;
/** Decode a base64 string to bytes; returns null on invalid input. */
export declare function decodeBase64Bytes(value: string): Uint8Array | null;
/** Decode a lowercase hex string to bytes; returns null on invalid input. */
export declare function decodeHexBytes(value: string): Uint8Array | null;