  Identification and authentication are two basic functionalities of
traditional random access protocols. In ALOHA-based random access, the packets
usually include a field with a unique user address. However, when the number of
users is massive and relatively small packets are transmitted, the overhead of
including such field becomes restrictive. In unsourced random access (U-RA),
the packets do not include any address field for the user, which maximizes the
number of useful bits that are transmitted. However, by definition an U-RA
protocol does not provide user identification. This paper presents a scheme
that builds upon an underlying U-RA protocol and solves the problem of user
identification and authentication. In our scheme, the users generate a message
authentication code (MAC) that provides these functionalities without violating
the main principle of unsourced random access: the selection of codewords from
a common codebook is i.i.d. among all users.
