International Association for Cryptologic Research

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TLS-Anvil: Adapting Combinatorial Testing for TLS Libraries

Authors:
Marcel Maehren
Philipp Nieting
Sven Hebrok
Robert Merget
Juraj Somorovsky
Jörg Schwenk
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Presentation: Slides
Abstract: Although the newest versions of TLS are considered secure, flawed implementations may undermine the promised security properties. Such implementation flaws result from the TLS specifications’ complexity, with exponentially many possible parameter combinations. Combinatorial Testing (CT) is a technique to tame this complexity, but it is hard to apply to TLS due to semantic dependencies between the parameters and thus leaves the developers with a major challenge referred to as the test oracle problem: Determining if the observed behavior of software is correct for a given test input. In this work, we present TLS-Anvil, a test suite based on CT that can efficiently and systematically test parameter value combinations and overcome the oracle problem by dynamically extracting an implementation-specific input parameter model (IPM) that we constrained based on TLS specific parameter value interactions. Our approach thus carefully restricts the available input space, which in return allows us to reliably solve the oracle problem for any combination of values generated by the CT algorithm. We evaluated TLS-Anvil with 13 well known TLS implementations, including OpenSSL, BoringSSL, and NSS. Our evaluation revealed two new exploits in MatrixSSL, five issues directly influencing the cryptographic operations of a session, as well as 15 interoperability issues, 116 problems related to incorrect alert handling, and 100 other issues across all tested libraries.
Video: https://youtu.be/WEjgFMuwIAc?t=2238
BibTeX
@misc{rwc-2023-35443,
  title={TLS-Anvil: Adapting Combinatorial Testing for TLS Libraries},
  note={Video at \url{https://youtu.be/WEjgFMuwIAc?t=2238}},
  howpublished={Talk given at RWC 2023},
  author={Marcel Maehren and Philipp Nieting and Sven Hebrok and Robert Merget and Juraj Somorovsky and Jörg Schwenk},
  year=2023
}