Product Overview The CryptoCompanion? Chip is designed as the mate to Atmel’s CryptoRF and CryptoMemory chips, collectively referred to in the remainder of this document as CRF. CryptoCompanion makes extensive use of the SHA-1 hash algorithm as specified in http://www.itl.nist.gov/fipspubs/fip180-1.htm and elsewhere. In this document, the nomenclature SHA-1(a, b, c) means to concatenate a, b & c in that order and then pad them to a block size of 64 bytes before computing the digest. CryptoCompanion generates SHA-1 digests of single round datasets at a time. 1.1. General Operation The CRF chip contains secrets that must be known or derived by a host system in order to establish a trusted link between the two and permit communications to happen. CryptoCompanion stores these secrets in an obscured way in nonvolatile memory and contains all the circuitry necessary to perform the authentication, password and encryption/decryption functions specified in the CRF datasheet. In this manner, the secrets do not ever need to be revealed. The general cryptographic strategy is as follows: ? Each CRF chip has a serial or identification number (ID) and authentication secret Gi stored in EEPROM. ID is freely readable while Gi can never be read and is unique for all tags. ? CryptoCompanion contains an EEPROM that holds a set of common secrets (Fn). CryptoCompanion combines Fn with ID and KID to compute a value of G that is expected to match that in the CRF chip. Specifically, G = SHA-1(Fn, ID, KID) ? G is further diversified by the inclusion of a number (KID) generated by the host system in a manner of its choosing. Typically, it will be the result of a cryptographic operation on the CRF ID value calculated using other data, secrets and/or algorithms external to CryptoCompanion. This permits scenarios that offer varying degrees of additional security. ? CryptoCompanion includes a general purpose cryptographic quality random number generator which is used to seed a mutual authentication process between CryptoCompanion and CRF. If the CRF confirms the CryptoCompanion challenge, and the CryptoCompanion confirms the CRF response, then the host system proceeds with CRF operations. In this way the host system may use the CRF without knowing the CRF's secrets directly.