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AG Codes and Kryptographie Bildinformationen anzeigen

AG Codes and Kryptographie

Offene Themen für Arbeiten

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Masterarbeiten

Improving features of anonymous communication

Many cryptographic systems, such as group signatures, have built-in privacy. For group signatures, this means that no polynomial-time adversary can, given a signature, find out who signed it (he only learns that some member of the group signed the message). In practice, the great measure of anonymity is diminished when used over the internet: if A sends an anonymous signature to B, then the signature itself does not reveal A's identity, but the IP address within the TCP packet does.

Using an anonymous communication system, a set of parties can communicate anonymously, i.e. the receiver of a message does not learn who sent it and the sender of a message only knows the receiver under some pseudonym. Today this is usually done using TOR. Recent research culminated in a new system that is based on trusted execution environments (such as Intel's SGX) and offers a much higher degree of security than TOR and other such schemes.

We suggest several possible extensions to this system:

  • Revocation of pseudonyms (using, for example, Bloom filters)
  • Efficiency improvements using network coding
  • Allow nodes to dynamically join or leave the system
  • ...

The thesis should deal with (some of) these extensions. Optionally, these ideas can be implemented into our existing prototype implementation (using the SGX SDK, language is C++).
There are initial ideas how to realize them, but there is lots of space for new ideas. The original construction uses ideas from both cryptography and overlay networks and is a nice application of both.

Bachelorarbeiten

Analyzing real-world applications of secure multiparty computation protocols

A recent case study ( https://eprint.iacr.org/2018/450.pdf ) considers the usage of secure multiparty computation (MPC) protocols in real-world applications. MPC protocols, in short, aim at enabling several parties to jointly evaluate a given function based on their private input data. In cryptography, such protocols are usually considered secure when nothing beyond the evaluated function's results is leaked during an execution. Security models vary in the abilities of adversaries, e.g. ranging from eavesdropping to adaptively corrupting and controlling a certain number or fraction of protocol participants. There exist several fundamental protocols which are applicable to any given (computable) function achieving different levels of security. However, their efficiency is often too low for practical applications.

To match real-world constraints, specialized MPC protocols and compositions thereof have been designed for certain use cases. The paper's authors, which also participated in the construction of the 4 considered products, only sketch their used techniques, matched (or at least desired) security properties and achieved performance. Interesting questions to be answered within a thesis, for example, are:

  • Which security models underly the products?
  • How do two similar products compare to each other (in terms of performance, functionality, security properties, ...)?
  • Have security properties been weakened for the sake of efficiency? If yes, where and why? 
  • How applicable are these products in reality, e.g. considering performance and usability? Are there other interesting products based on MPC protocols used in the wild?
  • ...? (Further suggestions)

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