/**
 * In-memory signature cache for Node.js SDK.
 * Caches Railgun wallet signatures to avoid re-deriving keys each operation.
 */
export declare function getCachedSignature(key: any): string | null;
export declare function setCachedSignature(key: any, signature: string): void;
export declare function clearSignatureCache(): void;
export declare function hasCachedSignature(key: any): boolean;