Timed-Release Encryption as a new primitive for security protocols

Lead Research Organisation: University of Oxford
Department Name: Computer Science


Timed-release encryption was introduced in 1993 by May[1] when he was trying to solve the problem of sending a message "into the future". The idea behind timed-release encryption is that you can encrypt a message which can only be decrypted after a given amount of time. Since 1993 many researchers tried to find new and different ways to construct timed-release ciphers and essentially only two approaches emerged: using a trusted third party (i.e. a central entity which is believed to be benevolent) or designing time-lock puzzles (i.e. puzzles which must require a minimum amount of time to be solved)[1].
The most obvious applications of timed-release encryption are related to sealed-bid auctions, key-escrow schemes and e-voting systems.[1,4]
However, recently a few research papers showed that timed-release encryption could be used in more settings. In [2] Roscoe takes advantage of this cryptographic primitive to design secure protocols where some malicious attacks can be distinguished from network failures. Alternatively, in [3], timed-release encryption is utilised to achieve some level of fairness in exchanging information between two parties.

My research aims to follow this more recent trend of using timed-release encryption as a cryptographic primitive in designing new protocols. In particular, my research will not focus on how to implement timed-release ciphers, but how different designs can be used in different settings to achieve desirable secure features.
In particular, I plan to research how the timed-release ciphers based on a trusted third party can be used in modern settings such as the IoT (Internet of Things) or blockchains to develop secure protocols. When designing protocols for the IoT, one must take into account that an adversary could easily have access to much more computing power than the small devices which constitute the IoT network. It follows that timed-release ciphers based on time-lock puzzles are likely to be impractical, hence the need to follow the approach relying on trusted third parties. To the best of my knowledge, this research area is largely unexplored as it follows the modern trend of taking advantage of timed-release ciphers to design new protocols but it diverges from the known papers by relying on a trusted third party rather than on time-lock puzzles. This novel approach to timed-release encryption could have a considerable impact if new secure protocols could be designed to be robust against quantum computing. In particular, many protocols rely on ciphers which are known to be easily broken by quantum computation and timed-release encryption can be built in quantum-safe ways using hashing as discussed in [5].
If these objectives are achieved, then this research could have a significant impact on modern technologies since security protocols can be applied easily to many different settings.

This project falls within the ESPRC Global uncertainties research area as it focuses on cyber-security.

[1] R. L. RIVEST, A. SHAMIR and D. A. WAGNER, Time-lock Puzzles and Timed-release Crypto, Massachusetts Institute of Technology, 1996.
[2] A. W. ROSCOE, Detecting Failed Attacks on Human-Interactive Security Protocols, Springer International Publishing, Cham, 2017, pp. 181-197.
[3] A. W. ROSCOE and P. Y. A. RYAN, Auditable PAKEs: Approaching Fair Exchange Without a TTP, Springer International Publishing, Cham, 2017, pp. 278-297.
[4] H. CHEN and R. DEVIANI, A Secure E-Voting System Based on RSA Time-Lock Puzzle Mechanism, 2012 Seventh International Conference on Broadband, Wireless Computing, Communication and Applications, 2012, pp. 596-601.
[5] G. BRANWEN, Time-lock encryption, Gwern.net, https://www.gwern.net/Self -decrypting-files#chained-hashes (last accessed Oct. 12, 2020)


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Project Reference Relationship Related To Start End Student Name
EP/R513295/1 01/10/2018 30/09/2023
2421791 Studentship EP/R513295/1 01/10/2020 31/03/2024 Ivo Maffei