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Appendix 2: Attacks on Factom
Denial of Service from Spam
Since Factom is an open system, any user can put Entries into almost any Chain. Bitcoin has a
similar phenomenon. In order for an Application to reject those transactions, the Application
would first need to download and process them. A large number of bogus Entries could slow
down the initial processing of the Application’s transactions. This threat is mitigated by an
attacker needing to spend money (resources) to carry it out. This is similar to Adam Back’s
Hashcash solution to email spam.
Audits are another useful tool against spam, if the application is willing to trade off security
versus convenience. Auditors could post “ignore” lists on the same chain, or create their own
audit chains with those lists. An auditor could use a profile chain to develop their reputation,
which would also allow review by other auditors. If any auditor made a bad call, it would be
easily verifiable and the record of it would be permanent. Some validity processing is gray, in
the sense that opinions may vary. Solving that problem would be implementation specific.
Sybil Attack of the DHT
Distributed Hash Tables in general are particularly susceptible to sybil attacks. An attacker could
create many peers which make it difficult for honest nodes to communicate. In a simplistic DHT
architecture, attackers can isolate a required piece of data from honest nodes. Sybil attacks
have been observed on the BitTorrent network routing table. The paper “Real-World Sybil
Attacks in BitTorrent Mainline DHT” detail these attacks. Fighting this type of attack is an active
topic in academic research. One mitigation technique uses complex lookup techniques to find
honest nodes among the sybils, studied in “Sybil-resistant DHT routing”. Some sybil mitigation
techniques rely on a web-of-trust by adding a social network to the routing table, as explored in
“A Sybil-proof one-hop DHT”. Factom will rely on the latest academic and open-source research
in this topic to secure its DHT.
Man in the Middle
There is a convention where the first Entry in a Chain can carry more significance than later
Entries. An attacker with a privileged position in the network can front run the original committer
by intercepting and getting an attack Chain creation request to the server prior to the authentic
request. This could be done with merely a faster connection to the relevant Factom Server.
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