### Strengthening Access Control Encryption

Christian Badertscher, Christian Matt, and Ueli Maurer

##### Abstract

Access control encryption (ACE) was proposed by Damgård et al. to enable the control of information flow between several parties according to a given policy specifying which parties are, or are not, allowed to communicate. By involving a special party, called the sanitizer, policy-compliant communication is enabled while policy-violating communication is prevented, even if sender and receiver are dishonest. To allow outsourcing of the sanitizer, the secrecy of the message contents and the anonymity of the involved communication partners is guaranteed. This paper shows that in order to be resilient against realistic attacks, the security definition of ACE must be considerably strengthened in several ways. A new, substantially stronger security definition is proposed, and an ACE scheme is constructed which provably satisfies the strong definition under standard assumptions. Three aspects in which the security of ACE is strengthened are as follows. First, CCA security (rather than only CPA security) is guaranteed, which is important since senders can be dishonest in the considered setting. Second, the revealing of an (unsanitized) ciphertext (e.g., by a faulty sanitizer) cannot be exploited to communicate more in a policy-violating manner than the information contained in the ciphertext. We illustrate that this is not only a definitional subtlety by showing how in known ACE schemes, a single leaked unsanitized ciphertext allows for an arbitrary amount of policy-violating communication. Third, it is enforced that parties specified to receive a message according to the policy cannot be excluded from receiving it, even by a dishonest sender.

Available format(s)
Publication info
A major revision of an IACR publication in ASIACRYPT 2017
DOI
10.1007/978-3-319-70694-8_18
Keywords
Access control encryptionInformation flow controlChosen-ciphertext attacks
Contact author(s)
mattc @ inf ethz ch
History
2017-11-30: last of 3 revisions
See all versions
Short URL
https://ia.cr/2017/429

CC BY

BibTeX

@misc{cryptoeprint:2017/429,
author = {Christian Badertscher and Christian Matt and Ueli Maurer},
title = {Strengthening Access Control Encryption},
howpublished = {Cryptology ePrint Archive, Paper 2017/429},
year = {2017},
doi = {10.1007/978-3-319-70694-8_18},
note = {\url{https://eprint.iacr.org/2017/429}},
url = {https://eprint.iacr.org/2017/429}
}

Note: In order to protect the privacy of readers, eprint.iacr.org does not use cookies or embedded third party content.