  Traditional covert transmission (CT) approaches have been hindering CT
application while blockchain technology offers new avenue. Current
blockchain-based CT approaches require off-chain negotiation of critical
information and often overlook the dynamic session keys updating, which
increases the risk of message and key leakage. Additionally, in some approaches
the covert transactions exhibit obvious characteristics that can be easily
detected by third-parties. Moreover, most approaches do not address the issue
of decreased reliability of message transmission in blockchain attack
scenarios. Bitcoin- and Ethereum-based approaches also have the issue of
transaction linkability, which can be tackled by Monero-based approaches
because of the privacy protection mechanisms in Monero. However, Monero-based
CT has the problem of sender repudiation. In this paper, we propose a novel
Monero-Based CT approach (MBCT), which enables on-chain session key dynamically
updating without off-chain negotiation. MBCT can assure non-repudiation of
transmission participants, confidentiality of keys, reliability of message
transmission and less observable characteristics. There are achieved by the
three components in MBCT, namely, a sender authentication method, a dynamically
on-chain session key updating method and a state feedback method. We implement
MBCT in Monero-0.18.1.0 and the experiment results demonstrate its high
embedding capacity of MBCT.
