Cryptographic Reverse Firewalls for Interactive Proof Systems
Chaya Ganesh, Bernardo Magri, and Daniele Venturi.
(Paper accepted at ICALP 2020)
Ganesh, Magri and Venturi study interactive proof systems (IPSes) in a strong adversarial setting where the machines of honest parties might be corrupted and under control of the adversary. Their aim is to answer the following, seemingly paradoxical, questions:
Can Peggy convince Vic of the veracity of an NP statement, without leaking any information about the witness even in case Vic is malicious and Peggy does not trust her computer?
Can we avoid that Peggy fools Vic into accepting false statements, even if Peggy is mali- cious and Vic does not trust her computer?
At EUROCRYPT 2015, Mironov and Stephens-Davidowitz introduced cryptographic reverse firewalls (RFs) as an attractive approach to tackling such questions. Intuitively, a RF for Peggy/Vic is an external party that sits between Peggy/Vic and the outside world and whose scope is to sanitize Peggy’s/Vic’s incoming and outgoing messages in the face of subversion of her/his computer, e.g. in order to destroy subliminal channels.
In this paper, the authors put forward several natural security properties for RFs in the concrete setting of IPSes. As their main contribution, they construct efficient RFs for different IPSes derived from a large class of Sigma protocols that we call malleable.
A nice feature of their design is that it is completely transparent, in the sense that our RFs can be directly applied to already deployed IPSes, without the need to re-implement them.
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