Paper 2019/1372

Analyzing the Linear Keystream Biases in AEGIS

Maria Eichlseder, Marcel Nageler, and Robert Primas


AEGIS is one of the authenticated encryption designs selected for the final portfolio of the CAESAR competition. It combines the AES round function and simple Boolean operations to update its large state and extract a keystream to achieve an excellent software performance. In 2014, Minaud discovered slight biases in the keystream based on linear characteristics. For family member AEGIS-256, these could be exploited to undermine the confidentiality faster than generic attacks, but this still requires very large amounts of data. For final portfolio member AEGIS-128, these attacks are currently less efficient than generic attacks. We propose improved keystream approximations for the AEGIS family, but also prove upper bounds below $2^{-128}$ for the squared correlation contribution of any single suitable linear characteristic.

Available format(s)
Secret-key cryptography
Publication info
Published by the IACR in FSE 2020
Authenticated encryptionCAESARAEGISLinear cryptanalysis
Contact author(s)
maria eichlseder @ iaik tugraz at
marcel nageler @ student tugraz at
rprimas @ gmail com
2019-12-01: received
Short URL
Creative Commons Attribution


      author = {Maria Eichlseder and Marcel Nageler and Robert Primas},
      title = {Analyzing the Linear Keystream Biases in AEGIS},
      howpublished = {Cryptology ePrint Archive, Paper 2019/1372},
      year = {2019},
      note = {\url{}},
      url = {}
Note: In order to protect the privacy of readers, does not use cookies or embedded third party content.