  We study the problem of efficiently disseminating authenticated blockchain
information from blockchain nodes (servers) to Internet of Things (IoT)
devices, through a wireless base station (BS). In existing blockchain
protocols, upon generation of a new block, each IoT device receives a copy of
the block header, authenticated via digital signature by one or more trusted
servers. Since it relies on unicast transmissions, the required communication
resources grow linearly with the number of IoT devices. We propose a more
efficient scheme, in which a single copy of each block header is multicasted,
together with the signatures of servers. In addition, if IoT devices tolerate a
delay, we exploit the blockchain structure to amortize the authentication in
time, by transmitting only a subset of signature in each block period. Finally,
the BS sends redundant information, via a repetition code, to deal with the
unreliable wireless channel, with the aim of decreasing the amount of feedback
required from IoT devices. Our analysis shows the trade-off between timely
authentication of blocks and reliability of the communication, depending on the
packet loss rate offered by the channel. The numerical results show that the
performance benefits of the proposed scheme makes it a viable starting point
for designing new lightweight protocols for blockchains.
