- We revisit a public key scheme presented by Shamir in  (and simultaneously by Naccache in ) and examine its applicability for general-purpose RFID tags in the supply chain. Using a combination of new and established space-saving methods, we present a full-fledged public key identification scheme, which is secure yet highly efficient. The 1024-bit scheme fits completely (including RAM) into 4682 gate equivalents and has a mean current consumption of 14.2μA. The main novelty in our implementation is the replacement of the long pseudo-random sequence, originally stored on 260 bytes of EEPROM in , by a reversible stream cipher using less than 300 bits of RAM. We show how our scheme offers tag-to-reader and reader-to-tag authentication and how it can be fit into the existing RFID supply chain infrastructure.