AT88SC018 Datasheet, PDF (2/33 Pages) ATMEL Corporation – CryptoCompanion™ Chip for CryptoMemory and CryptoRF

1. Product Overview
The AT88SC018 is designed as the mate to Atmel’s CryptoRF® (CRF) and CryptoMemory® (CM) chips, collectively
referred to in the remainder of this document as CRF. Within the operation descriptions, the AT88SC018
CryptoCompanion chip is sometimes referred to as CMC or CryptoMemory Companion chip.
The AT88SC018 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. The
AT88SC018 does not ever generate a SHA-1 digest of datasets larger than a single round
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. The AT88SC018 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 G_i stored in EEPROM. ID is freely
readable; G_i can never be read and is unique for all tags.
• The AT88SC018 contains an EEPROM that contains a set of common secrets (F_n). The AT88SC018 combines F_n
with ID and K_ID to compute a value of G that is expected to match that in the CRF chip. Specifically,
G = SHA-1(F_n, ID, K_ID)
• G is further diversified by the inclusion of a number (K_ID) 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 the AT88SC018. This permits scenarios that offer varying degrees of additional
security.
• The AT88SC018 includes a general purpose cryptographic quality random number generator which is used to seed a
mutual authentication process between the AT88SC018 and CRF. If the CRF confirms the CMC challenge, and the
CMC 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.
1.2.
CryptoCompanion Benefits
The following is a partial list of the benefits of using this chip versus storing the algorithms and secrets in standard
FLASH system memory.
• Keep confidential those core secrets that are used to authenticate with and communicate to/from CRF.
(Store them in EEPROM, use them on-chip)
• Flexible system implementation – multiple secrets and policies for different CRF locations within the system.
Multiple manufacturer setup options.
• Hardware encryption engines, avoids algorithm disclosure from reverse-compilation of system operating code.
• Full hardware security implementation makes it harder for an attacker (even with lab equipment) to get secrets stored
on the AT88SC018.
• Global secrets are protected using strong security, standard algorithm (SHA-1).
• Implements a crunching algorithm to prevent micro-controller based CRF replicas.
• Robust random number generation avoids accidental replay for all cryptographic operations using the system, not
just with respect to CRF.
2 CryptoCompanion Chip
5277C–CryptoCompanion–9/09