Don't miss our weekly PhD newsletter | Sign up now Don't miss our weekly PhD newsletter | Sign up now

  Reductions in Cryptography: Subversion Resilience


   School of Computer Science

   Applications accepted all year round  Funded PhD Project (UK Students Only)

About the Project

The security of a modern cryptographic construction is proved via a reduction from the hardness of solving some well-studied mathematical problems. There is, however, a substantial gap between security proved in theory and security achieved in practice. In general theoretical analysis, the integrity of algorithms and the secrecy of the keys are always assumed to hold. In fact, guarantees of semantic security of many popular and widely deployed cryptosystems may break down if the adversary sees encryptions of the secret key. In practice, on the other hand, the algorithms may be tampered with to modify a few bits of the keys, commonly known as the related-key attacks, or to leak encryptions of (some function of) the secret key, commonly known as the key-dependent message attacks. The adversary may even tamper with the algorithms in such a way that a small fraction of outputs is subverted, a generalisation of the kleptographic attacks. A line of work has considered the security of cryptosystems in the presence of such key-dependent messages or subverted algorithms. However, practical and deployable cryptographic solutions against such active attacks are still missing for many fundamental problems.

The objective of the project is to analyse the security of deployed cryptosystems along with designing new ones that can withstand key-correlated attacks and general kleptographic attacks. In particular, we wish to address the following.

1. Efficient and secure authentication mechanisms against key-correlated and misuse-resistant attacks. The project will analyse deployed and standardised MAC (message authentication code) algorithms and authenticated encryptions in the light of simultaneous related-key and key-dependent message attacks.

2. Design principles of key encapsulation mechanisms resisting kleptographic attack. Recent kleptographic attacks against the key encapsulation mechanisms have shown a significant vulnerability of the hybrid encryption protocols. We shall explore whether the widely deployed Fujisaki-Okamoto transformation could be salvaged to achieve security against such kleptographic attacks.

3. Secure modes of operation of hash functions and block ciphers resisting kleptographic attack. Security of modes of operations of hash functions and block ciphers often require the underlying primitive to behave like a random function or a random permutation. We shall analyse the security of these modes when the underlying primitives are modified via a kleptographic attack.

Computer Science (8) Mathematics (25)

References

Subversion Resilient Hashing: Efficient Constructions and Modular Proofs for Crooked Indifferentiability
Rishiraj Bhattacharyya, Mridul Nandi, Anik Raychaudhuri, IEEE Transactions on Information Theory 2023.
Crooked Indifferentiability of Enveloped XOR revisited
Rishiraj Bhattacharyya, Mridul Nandi, Anik Raychaudhuri, Indocrypt 2021.
Memory-Tight Reductions for Practical Key Encapsulation Mechanisms
Rishiraj Bhattacharyya, PKC 2020.

Open Days


Register your interest for this project



How good is research at University of Birmingham in Computer Science and Informatics?


Research output data provided by the Research Excellence Framework (REF)

Click here to see the results for all UK universities
Search Suggestions
Search suggestions

Based on your current searches we recommend the following search filters.