Paper 2021/923

On the (in)security of ElGamal in OpenPGP

Luca De Feo, Bertram Poettering, and Alessandro Sorniotti


Roughly four decades ago, Taher ElGamal put forward what is today one of the most widely known and best understood public key encryption schemes. ElGamal encryption has been used in many different contexts, chiefly among them by the OpenPGP standard. Despite its simplicity, or perhaps because of it, in reality there is a large degree of ambiguity on several key aspects of the cipher. Each library in the OpenPGP ecosystem seems to have implemented a slightly different "flavour" of ElGamal encryption. While --taken in isolation-- each implementation may be secure, we reveal that in the interoperable world of OpenPGP, unforeseen cross-configuration attacks become possible. Concretely, we propose different such attacks and show their practical efficacy by recovering plaintexts and even secret keys.

Available format(s)
Cryptographic protocols
Publication info
Published elsewhere. Minor revision. CCS 2021
OpenPGPElGamal encryptioncryptanalysisDLPside-channel attack
Contact author(s)
poe @ zurich ibm com
2021-07-09: received
Short URL
Creative Commons Attribution


      author = {Luca De Feo and Bertram Poettering and Alessandro Sorniotti},
      title = {On the (in)security of ElGamal in OpenPGP},
      howpublished = {Cryptology ePrint Archive, Paper 2021/923},
      year = {2021},
      note = {\url{}},
      url = {}
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