Paper 2023/1519

Accountable Decryption made Formal and Practical

Rujia Li, Tsinghua University
Yuanzhao Li, Southern University of Science and Technology
Qin Wang, UNSW Sydney
Sisi Duan, Tsinghua University
Qi Wang, Southern University of Science and Technology
Mark Ryan, University of Birmingham

With the increasing scale and complexity of online activities, accountability, as an after-the-fact mechanism, has become an effective complementary approach to ensure system security. Decades of research have delved into the connotation of accountability. They fail, however, to achieve practical accountability of decryption. This paper seeks to address this gap. We consider the scenario where a client (called encryptor, her) encrypts her data and then chooses a delegate (a.k.a. decryptor, him) that stores data for her. If the decryptor initiates an illegitimate decryption on the encrypted data, there is a non-negligible probability that this behavior will be detected, thereby holding the decryptor accountable for his decryption. We make three contributions. First, we review key definitions of accountability known so far. Based on extensive investigations, we formalize new definitions of accountability specifically targeting the decryption process, denoted as accountable decryption, and discuss the (in)possibilities when capturing this concept. We also define the security goals in correspondence. Secondly, we present a novel Trusted Execution Environment(TEE)-assisted solution aligning with definitions. Instead of fully trusting TEE, we take a further step, making TEE work in the "trust, but verify" model where we trust TEE and use its service, but empower users (i.e., decryptors) to detect the potentially compromised state of TEEs. Thirdly, we implement a full-fledged system and conduct a series of evaluations. The results demonstrate that our solution is efficient. Even in a scenario involving $300,000$ log entries, the decryption process concludes in approximately $5.5$ms, and malicious decryptors can be identified within $69$ms.

Available format(s)
Cryptographic protocols
Publication info
AccountabilityDecryptionTrusted Hardware
Contact author(s)
rujia @ tsinghua edu cn
bravochaos418 @ gmail com
qinwangtech @ gmail com
duansisi @ mail tsinghua edu cn
wangqi @ sustech edu cn
m d ryan @ bham ac uk
2024-03-26: revised
2023-10-05: received
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Creative Commons Attribution


      author = {Rujia Li and Yuanzhao Li and Qin Wang and Sisi Duan and Qi Wang and Mark Ryan},
      title = {Accountable Decryption made Formal and Practical},
      howpublished = {Cryptology ePrint Archive, Paper 2023/1519},
      year = {2023},
      note = {\url{}},
      url = {}
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