The Signal Protocol for non-Cryptographers: An Explanation of the Signal Protocol and its Security Properties
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Typ
Examensarbete för masterexamen
Program
Computer science – algorithms, languages and logic (MPALG), MSc
Publicerad
2019
Författare
Yagublu, Lamiya
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
People tend to socialize and today many people use messaging applications to
communicate. While people communicate, they share personal information between
each other and they do not want others to observe or access their information and
use it against them. Therefore, it is important to keep this information private. The
Signal protocol is a communication protocol used to provide security guarantees and
keep the users’ information private while they communicate. Since many messaging
applications, including WhatsApp and Facebook messenger, uses the Signal protocol
and a lot of people use these applications, any flaw in the Signal protocol might affect
a large number of users’ private communication.
This master thesis aims to study the Signal protocol and explains, in an easy way,
its functionality and security properties. The thesis contains a detailed explanation
of the core parts of the Signal protocol and its security. A literature review was
conducted to investigate how the Signal protocol works and what kind of security
properties it has. Due to complexity of the problem in the few academic papers, the
Signal protocol is defined and explained in an easier way. The thesis focuses mainly
on the academic paper titled "A Formal Security Analysis of the Signal Messaging
Protocol" by K. Cohn-Gordon, C. Cremers, B. Dowling, L. Garratt and D. Stebila.
As a technical contribution of this thesis, the existing notation from the above
mentioned paper is revisited and simplified. Thereafter, the new and simplified
notation is used to explain how the Signal protocol works in an easy way. The explanation
with the simplified notations helps non-technical people to understand the
protocol better. Then the security properties of the Signal protocol are investigated
and explained.
Beskrivning
Ämne/nyckelord
Signal , instant messaging , key distribution system , double ratchet , forward Secrecy , post-compromised security , end-to-end encryption , authenticated encryption with associated data