/**
 * symmetric encryption
 * @param  plaintext     input text to be encrypted
 * @param  key           serectKey string in hex (16 btyes)
 * @param  iv            iv string in hex (16 btyes because of AES 128bit blocksize)
 * @param  algo='aes256' symmetric encryption algo, defualt is AES256
 * @return encrypted ciphertext in hex (48 btyes)
 */
export declare function encrypt(plaintext: string, key: string, iv: string, algo?: string): string;
/**
 * symmetric decryption
 * @param  encrypted     encrypted ciphertext in hex (48 btyes)
 * @param  key           serectKey string in hex (16 btyes)
 * @param  iv            iv string in hex (16 btyes because of AES 128bit blocksize)
 * @param  algo='aes256' symmetric encryption algo, defualt is AES256
 * @return decrypted text in hex
 */
export declare function decrypt(encrypted: string, // 48 bytes
key: string, // derivedKey 16 bytes
iv: string, // 16 btyes
algo?: string): string;
/**
 * randomly generate iv
 * @param  length default length is 16 btyes because of AES 128bit blocksize
 * @return iv in hex
 */
export declare function generateIv(length?: number): string;