Toward secure implementation of mcEliece decryption

Abstract

We analyse the security regarding timing attacks of implementations of the decryption in McEliece PKC with binary Goppa codes. First, we review and extend the existing attacks, both on the messages and on the keys. We show that, until now, no satisfactory countermeasure could erase all the timing leakages in the Extended Euclidean Algorithm (EEA) step. Then, we describe a version of the EEA never used for McEliece so far. It uses a constant number of operations for given public parameters. In particular, the operation flow does not depend on the input of the decryption, and thus closes all previous timing attacks. We end up with what should become a central tool toward a secure implementation of McEliece decryption.