Impact
kyber512, kyber768, and kyber1024 only: An attacker able to submit many decapsulation requests against a single private key, and to gain timing information about the decapsulation, could recover the private key. Proof-of-concept exploit exists for a local attacker.
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N/E:P/RL:O/RC:C
Patches
Version 0.0.6.1 and newer of PyPQC is patched.
Workarounds
No workarounds have been reported. The 0.0.6 -> 0.0.6.1 upgrade should be a drop-in replacement; it has no known breaking changes.
References
Timeline
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Cryspen researchers privately reported KyberSlash to the reference implementation maintainers.
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Peter Schwabe partially patched KyberSlash (only "KyberSlash 1") in the reference implementation on December 1st, 2023, but did not document or advertise this as a security patch.
https://www.github.com/pq-crystals/kyber/commit/dda29cc63af721981ee2c831cf00822e69be3220
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Daniel J. Bernstein publicly reported KyberSlash as a security issue on December 15th, 2023.
https://groups.google.com/a/list.nist.gov/g/pqc-forum/c/hWqFJCucuj4/m/-Z-jm_k9AAAJ
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Daniel J. Bernstein created a webpage for authoritative reference about KyberSlash on December 19th, 2023.
https://kyberslash.cr.yp.to/
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Thom Wiggers acknowledged KyberSlash as a security issue on December 19th, 2023.
https://www.github.com/PQClean/PQClean/issues/533
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Prasanna Ravi and Matthias Kannwischer privately reported further details about KyberSlash ("KyberSlash 2") to the reference implementation maintainers.
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Peter Schwabe completely patched KyberSlash in the reference implementation on December 29th, 2023.
https://www.github.com/pq-crystals/kyber/commit/11d00ff1f20cfca1f72d819e5a45165c1e0a2816
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Prasanna Ravi and Matthias Kannwischer publicly reported their findings ("KyberSlash 2") on December 30th, 2023.
https://groups.google.com/a/list.nist.gov/g/pqc-forum/c/ldX0ThYJuBo/m/ovODsdY7AwAJ
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Daniel J. Bernstein published a proof-of-concept exploit (only validated for a local attacker) for KyberSlash on December 30th, 2023.
https://groups.google.com/a/list.nist.gov/g/pqc-forum/c/ldX0ThYJuBo/m/uIOqRF5BAwAJ
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Thom Wiggers completely patched KyberSlash in PQClean on January 25th, 2024.
https://www.github.com/PQClean/PQClean/commit/3b43bc6fe46fe47be38f87af5019a7f1462ae6dd
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James E. A. completely patched KyberSlash in pypqc and released a security update on January 26th, 2024.
https://www.github.com/JamesTheAwesomeDude/pypqc/commit/b33fec8cd36e865f8db6215c64b2d01f429a1ed6
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