Paper 2013/157

The fragility of AES-GCM authentication algorithm

Shay Gueron and Vlad Krasnov


A new implementation of the GHASH function has been recently committed to a Git version of OpenSSL, to speed up AES-GCM. We identified a bug in that implementation, and made sure it was quickly fixed before trickling into an official OpenSSL trunk. Here, we use this (already fixed) bug as a real example that demonstrates the fragility of AES-GCM’s authentication algorithm (GHASH). One might expect that incorrect MAC tag generation would only cause legitimate message-tag pairs to fail authentication (which is already a serious problem). However, since GHASH is a “polynomial evaluation” MAC, the bug can be exploited for actual message forgery.

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Publication info
Published elsewhere. Unknown where it was published
AES-GCMGHASHpolynomial evaluation MACmessage forgeryOpenSSL
Contact author(s)
shay @ math haifa ac il
2013-03-26: received
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Creative Commons Attribution


      author = {Shay Gueron and Vlad Krasnov},
      title = {The fragility of AES-GCM authentication algorithm},
      howpublished = {Cryptology ePrint Archive, Paper 2013/157},
      year = {2013},
      note = {\url{}},
      url = {}
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