Fast Key Recovery Attack on ARMADILLO1 and Variants

The ARMADILLO cryptographic primitive is a multi-purpose cryptographic primitive for RFID devices proposed at CHES’10. The main purpose of the primitive is to provide a secure authentication in a challenge-response protocol. It has two versions, named ARMADILLO (subsequently denoted by ARMADILLO1) and ARMADILLO2. However, we found a fatal weakness in the design which allows a passive attacker to recover the secret key in polynomial time, of ARMADILLO1 and some generalizations. We introduce some intermediate designs which try to prevent the attack and link ARMADILLO1 to ARMADILLO2. Considering the fact that the attack against ARMADILLO1 is polynomial, this brings about some concerns into the security of the second version ARMADILLO2, although it remains unbroken so far.