/**
 * @param key       unique secret key for user
 * @param algorithm custom algorithm for crypto.createHmac. Default: sha1
 * @param counter   moving factor. Default: 0
 * @return 6 digit code as a string
 */
export declare const generate:({key,algorithm,counter}:{key:string|Buffer;algorithm?:string;counter?:number;})=>string;
/**
 * @param token     code, provided by user
 * @param key       unique secret key for user
 * @param algorithm custom algorithm for crypto.createHmac. Default: sha1
 * @param window    counter values window. Default: 1
 * @param counter   moving factor. Default: 0
 * @return null if nothing found or number between -window to +window if same code in steps found
 */
export declare const validate:({token,key,algorithm,window,counter,}:{token:string;key:string|Buffer;algorithm?:string;window?:number;counter?:number;})=>number|null;