  The traditional Domain Name System (DNS) lacks fundamental features of
security and privacy in its design. As concerns of privacy increased on the
Internet, security and privacy enhancements of DNS have been actively
investigated and deployed. Specially for user's privacy in DNS queries, several
relay-based anonymization schemes have been recently introduced, however, they
are vulnerable to the collusion of a relay with a full-service resolver, i.e.,
identities of users cannot be hidden to the resolver. This paper introduces a
new concept of a multiple-relay-based DNS for user anonymity in DNS queries,
called the mutualized oblivious DNS ($\mu$ODNS), by extending the concept of
existing relay-based schemes. The $\mu$ODNS introduces a small and reasonable
assumption that each user has at least one trusted/dedicated relay in a network
and mutually shares the dedicated one with others. The user just sets the
dedicated one as his next-hop, first relay, conveying his queries to the
resolver, and randomly chooses its $0$ or more subsequent relays shared by
other entities. Under this small assumption, the user's identity is concealed
to a target resolver in the $\mu$ODNS even if a certain (unknown) subset of
relays collude with the resolver. That is, in $\mu$ODNS, users can preserve
their privacy and anonymity just by paying a small cost of sharing its
resource. Moreover, we present a PoC implementation of $\mu$ODNS that is
publicly available on the Internet. We also show that by measurement of
round-trip-time for queries, and our PoC implementation of $\mu$ODNS achieves
the performance comparable to existing relay-based schemes.
