2

CryptoCompanion Chip

5277C–CryptoCompanion–9/09

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

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:

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.