For purposes of authentication and automatic identification using iButton devices, the DS1990 is the lowest security available. It consists of a guaranteed unique number that can be assigned to an object and can be read electronically for identification and electronic record keeping. The DS1991 is a step above the DS1990 in security. It contains a unique id number and has password-protected memory areas. It ranks below the DS1961S. In iButton form the DS1961S is the strongest authentication method Maxim makes (in chip form SHA-256 or ECDSA chips offer stronger forms of authentication, but these are not available in the iButton form factor).