Cryptology ePrint Archive: Report 2018/747

Pseudo Constant Time Implementations of TLS Are Only Pseudo Secure

Eyal Ronen and Kenneth G. Paterson and Adi Shamir

Abstract: Today, about 10% of TLS connections are still using CBC-mode cipher suites, despite a long history of attacks and the availability of better options (e.g. AES-GCM). In this work, we present three new types of attack against four popular fully patched implementations of TLS (Amazon's s2n, GnuTLS, mbed TLS and wolfSSL) which elected to use ``pseudo constant time'' countermeasures against the Lucky 13 attack on CBC-mode. Our attacks combine several variants of the PRIME+PROBE cache timing technique with a new extension of the original Lucky 13 attack. They apply in a cross-VM attack setting and are capable of recovering most of the plaintext whilst requiring only a moderate number of TLS connections. Along the way, we uncovered additional serious (but easy to patch) bugs in all four of the TLS implementations that we studied; in three cases, these bugs lead to Lucky 13 style attacks that can be mounted remotely with no access to a shared cache. Our work shows that adopting pseudo constant time countermeasures is not sufficient to attain real security in TLS implementations in CBC mode.

Category / Keywords: implementation / Lucky 13 attack, TLS, Side-channel cache attacks, Plaintext recovery

Original Publication (in the same form): CCS ’18: 2018 ACM SIGSAC Conference on Computer & Communications Security

Date: received 11 Aug 2018, last revised 16 Aug 2018

Contact author: eyal ronen at weizmann ac il

Available format(s): PDF | BibTeX Citation

Version: 20180817:112937 (All versions of this report)

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