The work in this thesis examines protocols designed to
address the issues of tracing illegal distribution of digital content in a fair manner.

In digital content distribution, a client requests
content from a distributor, and the distributor sends content to the client.
The main concern is misuse of content by the client, 
such as illegal distribution.
As a result, digital watermarking schemes that enable the distributor 
to trace copies of content and identify the perpetrator were proposed.
However, such schemes do not provide a mechanism for the distributor
to prove to a third party that a client illegally distributed copies of content.
Furthermore, it is possible that the distributor falsely 
accuses a client as he has total control of the tracing mechanisms.
Fair content tracing (FaCT) 
protocols were thus proposed to allow tracing of content that
does not discriminate either the distributor or the client. 

Many FaCT protocols have been proposed, mostly without an appropriate 
design framework, and so there is no obvious and systematic way to evaluate them.
Therefore, we propose a framework that provides a definition 
of security and which enables classification of FaCT protocols so
that they can be analysed in a systematic manner.
We define, based on our framework, four main categories of FaCT 
protocols and propose new approaches to designing them.

The first category is protocols without trusted third parties.
As the name suggests, these protocols do not rely on a
central trusted party for fair tracing of content.
It is difficult to design such a protocol without drawing on
extra measures that increase communication and computation costs.
We show this is the case by demonstrating flaws in two recent proposals.
We also illustrate a possible repair based on relaxing 
the assumption of trust on the distributor.

The second category is protocols with online trusted third parties,
where a central online trusted party is deployed.
This means a trusted party must always be available during
content distribution between the distributor and the client.
While the availability of a trusted third party may simplify
the design of such protocols, efficiency may suffer due to the
need to communicate with this third party. 

The third category is protocols with offline trusted third parties,
where a central offline trusted party is deployed.
The difference between the offline and the online trusted party is
that the offline trusted party need not be available during content distribution.
It only needs to be available during the initial setup and 
when there is a dispute between the distributor and the client.
This reduces the communication requirements compared to using an online trusted party.
Using a symmetric-based cryptographic primitive known as
Chameleon encryption, we proposed a new approach to 
designing such protocols.

The fourth category is protocols with trusted hardware.
Previous protocols proposed in this category have abstracted away from
a practical choice of the underlying trusted hardware.
We propose new protocols based on a Trusted Platform Module (TPM).

Finally, we examine the inclusion of payment in a FaCT protocol,
and how adding payment motivates the requirement for
fair exchange of buying and selling digital content.