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Partitioning Oracle Attacks

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Inclusion.

Authors: 

Julia Len, Paul Grubbs, and Thomas Ristenpart, Cornell Tech

Abstract: 

In this paper we introduce partitioning oracles, a new class of
decryption error oracles which, conceptually, take a ciphertext as
input and output whether the decryption key belongs to some known
subset of keys. Partitioning oracles can arise when encryption
schemes are not committing with respect to their keys. We detail
adaptive chosen ciphertext attacks that exploit partitioning oracles
to efficiently recover passwords and de-anonymize anonymous
communications. The attacks utilize efficient key multi-collision
algorithms--a cryptanalytic goal that we define--against widely used
authenticated encryption with associated data (AEAD) schemes,
including AES-GCM, XSalsa20/Poly1305, and ChaCha20/Poly1305.

We build a practical partitioning oracle attack that quickly recovers
passwords from Shadowsocks proxy servers. We also survey early
implementations of the OPAQUE protocol for password-based key
exchange, and show how many could be vulnerable to partitioning
oracle attacks due to incorrectly using non-committing AEAD. Our
results suggest that the community should standardize and make widely
available key-committing AEAD to avoid such vulnerabilities.

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BibTeX
@inproceedings {263884,
title = {Partitioning Oracle Attacks},
booktitle = {30th {USENIX} Security Symposium ({USENIX} Security
21)},
year = {2021},
address = {Vancouver, B.C.},
url = {https://www.usenix.org/conference/usenixsecurity21/
presentation/len},
publisher = {{USENIX} Association},
month = aug,
}
Download
PDF icon Len Paper (Prepublication) PDF

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