Securing Data Integrity in
Modern Overlay Networks
an Integrated Perspective from Theory to Practice
Zhongtang Luo
Purdue University
Data Integrity
Traditionally…
Data integrity
is
a multi-party problem
in modern
networks
Decentralized Anonymous Communication
~2 million users
Tor Directory Protocol
2004–2006
Client asks one directory authority
What if one authority is compromised?
2006–2007
Client asks nine directory authorities
9x bandwidth overhead
2008–now
Nine authorities communicate and sign a consensus document
We are the first to conduct a systematic documentation and study of the protocol [LBNK24]
[LBNK24] Attacking and Improving the Tor Directory Protocol (IEEE SP'24)
We discover a
critical vulnerability
that allows any single authority to corrupt relay information to
deanonymize users by equivocating
We implemented and merged a lightweight fix that detects equivocation by checking the message sent from each authority
Source: https://gitlab.torproject.org/tpo/network-health/depictor/-/merge_requests/1
In our subsequent work [LZNK25], we discover a DDoS attack that disables the directory protocol through 5 minutes of attack, highlighting the need for a re-design of the protocol based on robust assumptions
[LZNK25] Five Minutes of DDoS Brings down Tor: DDoS Attacks on the Tor Directory Protocol and Mitigations
Partial Synchrony
After some unknown global synchronization time (GST), every sent message is received within a known time bound $\Delta$
Safe
in bad network
Live
in good network
Interactive Consistency under Partial Synchrony [LZNK25]
Guarantees delivery of every message from a correct sender when GST is
zero
Guarantees delivery of $(n-f)$ messages when GST is
non-zero
[LZNK25] Five Minutes of DDoS Brings down Tor: DDoS Attacks on the Tor Directory Protocol and Mitigations
We also propose a protocol that achieves interactive consistency under partial synchrony, and implemented a Rust prototype
Robust assumptions translate to security wins: our prototype has a comparable latency while being immune to DDoS attacks in the paper
Data integrity
is
a multi-party problem
in modern
networks
Decentralized Anonymous Communication
~2 million users
Decentralized Social Networking
~10 million users
Cryptocurrency
~$4 Trillion Market Cap
How do we define data integrity in an increasingly decentralized network?
Beyond that …
Source: https://x.com/PR0GRAMMERHUM0R/status/1656766152817737733/
Is this screenshot real?
TLS Oracle
The user may not want to expose their secrets
The user may trick the system into believing misinterpreted data
Connection to the server may be hijacked
Source: https://medium.com/@justinomora/demystifying-the-signal-protocol-for-end-to-end-encryption-e2ee-ad6a567e6cb4
Can Signal distribute fake keys to spy on people?
Key Transparency
Encryption
Keys
Center
Integrated Innovation in Data Integrity
Cryptographic
Foundation
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Protocol
Design
Find and achieve application goals
Security
Analysis
Examine and study existing systems