import { getBase58FromAddress } from '../keyring';
/**
 * Re-export address to pubkey conversion from keyring
 */
export { getBase58FromAddress as addressToPubkeyBase58 };
/**
 * Check if a value is not null, undefined, or empty string
 */
export declare function isNotNilOrBlank(value: unknown): value is string;
/**
 * Calculate SHA256 hash of a string and return as uppercase hex
 * Uses Web Crypto API (works in Node.js and browsers)
 * @param content - String content to hash
 * @returns Uppercase hex string of SHA256 hash
 */
export declare function calculateHash(content: string): Promise<string>;
/**
 * Sign a hash using the provided sign function
 * @param hash - Hash string to sign
 * @param signFunction - Function that signs bytes and returns signature
 * @returns Base64 encoded signature
 */
export declare function signHash(hash: string, signFunction: (message: Uint8Array) => Promise<Uint8Array>): Promise<string>;
/**
 * Convert Uint8Array to base64 string
 * Works in both Node.js and browser environments
 */
export declare function uint8ArrayToBase64(bytes: Uint8Array): string;
/**
 * Convert base64 string to Uint8Array
 * Works in both Node.js and browser environments
 */
export declare function base64ToUint8Array(base64: string): Uint8Array;
/**
 * Build avatar data URL from avatar object
 * @param avatar - Avatar object with content type and base64 content
 * @param avatar._content_type - MIME type of the avatar content
 * @param avatar._content - Base64 encoded avatar content
 * @returns Data URL string or null
 */
export declare function buildAvatarDataUrl(avatar?: {
    _content_type?: string;
    _content?: string;
}): string | null;
/**
 * Prepend hash and signature to JSON string (CesiumPlus requirement)
 * The API expects hash and signature as the first fields
 */
export declare function prependHashAndSignature(jsonString: string, hash: string, signature: string): string;
/**
 * Get current Unix timestamp in seconds
 */
export declare function getCurrentTimestamp(): number;