Post-Quantum Multi-Recipient Public Key Encryption
Joël Alwen, Dominik Hartmann, Eike Kiltz, Marta Mularczyk, Peter Schwabe · 2023
A multi-message multi-recipient PKE (mmPKE) encrypts a batch of messages, in one go, to a corresponding set of independently chosen receiver public keys. The resulting ''multi-recipient ciphertext'' can be then be reduced (by any 3rd party) to a shorter, receiver specific, ''invidual ciphertext.'' Finally, to recover the i-th message in the batch from their indvidual ciphertext the i-th receiver only needs their own decryption key. A special case of mmPKE is multi-recipient PKE (mPKE) where all receivers are sent the same message. By treating (m)mPKE and their KEM counterparts as a stand-alone primitives we allow for more efficient constructions than trivially composing individual PKE/KEM instances. This is especially valuable in the post-quantum setting, where PKE/KEM ciphertexts and public keys tend to be far larger than their classic counterparts.