Gladius: LWR-based efficient hybrid public key encryption with distributed decryption

January 25, 2022

Daniele Cozzo


Gladius: LWR-based efficient hybrid public key encryption with distributed decryption

Time:   11:00am
Location:   Lecture hall 1
Virtual transmission:   Zoom3 https://zoom.us/j/3911012202
Pass:   s3

Standard hybrid encryption schemes based on the KEM-DEM framework are hard to implement efficiently in a distributed manner while maintaining the CCA security property of the scheme. This is because the DEM needs to be decrypted under the key encapsulated by the KEM, before the whole ciphertext is declared valid. In this paper we present a new variant of the KEM-DEM framework, closely related to Tag-KEMs, which sidesteps this issue. We then present a post-quantum KEM for this framework based on Learning-with-Rounding, which is designed specifically to have fast distributed decryption. Our combined construction of a hybrid encryption scheme with Learning-with-Rounding based KEM, called Gladius, is closely related to the NIST Round 3 candidate called Saber. We wrote prototype distributed implementation that achieves a decapsulation time of 4.99 seconds for three parties.