/**
 * Generate a cryptographically secure random string for authorization keys.
 */
export declare function generateSecureKey(length?: number): string;
/**
 * Hash a plain text key with SHA-256 for secure database storage.
 */
export declare function hashKey(key: string): string;
/**
 * Constant-time hash verification to prevent timing attacks.
 */
export declare function verifyKeyHash(key: string, storedHash: string): boolean;