  Increasing awareness of privacy-preserving has led to a strong focus on
anonymous systems protecting anonymity. By studying early schemes, we summarize
some intractable problems of anonymous systems. Centralization setting is a
universal problem since most anonymous system rely on central proxies or
presetting nodes to forward and mix messages, which compromises users' privacy
in some way. Besides, availability becomes another important factor limiting
the development of anonymous system due to the large requirement of additional
additional resources (i.e. bandwidth and storage) and high latency. Moreover,
existing anonymous systems may suffer from different attacks including
abominable Man-in-the-Middle (MitM) attacks, Distributed Denial-of-service
(DDoS) attacks and so on. In this context, we first come up with a
BlockChain-based Mix-Net (BCMN) protocol and theoretically demonstrate its
security and anonymity. Then we construct a concrete dynamic self-organizing
BlockChain-based MIX anonymous system (BCMIX). In the system, users and mix
nodes utilize the blockchain transactions and their addresses to negotiate keys
with each other, which can resist the MitM attacks. In addition, we design an
IP sharding algorithm to mitigate Sybil attacks. To evaluate the BCMIX system,
we leverage the distribution of mining pools in the real world to test the
system's performance and ability to resistant attacks. Compared with other
systems, BCMIX provides better resilience to known attacks, while achieving low
latency anonymous communication without significant bandwidth or storage
resources.
