AT88SC0204C-SU ATMEL [ATMEL Corporation], AT88SC0204C-SU Datasheet - Page 12

• Manufacturer Part Number: AT88SC0204C-SU
• Description: CryptoMemory 2 Kbit
• Manufacturer: ATMEL [ATMEL Corporation]

Checksum
Encryption
Supervisor Mode
Modify Forbidden
Program Only
Initial Device
Programming
12
AT88SC0204C
The AT88SC0204C implements a data validity check function in the form of a check-
sum, which may function in standard, authentication or encryption modes.
In the standard mode, the checksum is implemented as a Modification Detection Code
(MDC), in which the host may read an MDC from the device in order to verify that the
data sent was received correctly.
In the authentication and encryption modes, the checksum becomes more powerful
since it provides a bidirectional data integrity check and data origin authentication capa-
bility in the form of a Message Authentication Code (MAC). Only the host/device that
carried out a valid authentication is capable of computing a valid MAC. While operating
in the authentication or encryption modes, the use of a MAC is required. For an ingoing
command, if the device calculates a MAC different from the MAC transmitted by the
host, not only is the command abandoned but the mode is also reset. A new authentica-
tion and/or encryption activation will be required to reactivate the MAC.
The data exchanged between the device and the host during read, write and verify
password commands may be encrypted to ensure data confidentiality.
The issuer may choose to require encryption for a user zone by settings made in the
configuration memory. Any one of four keys may be selected for use with a user zone. In
this case, activation of the encryption mode is required in order to read/write data in the
zone and only encrypted data will be transmitted. Even if not required, the host may
elect to activate encryption provided the proper keys are known.
Enabling this feature allows the holder of one specific password to gain full access to all
eight password sets, including the ability to change passwords.
No write access is allowed in a user zone protected with this feature at any time. The
user zone must be written during device personalization prior to blowing the security
fuses.
For a user zone protected by this feature, data within the zone may be changed from a
“1” to a “0”, but never from a “0” to a “1”.
To enable the security features of CryptoMemory, the device must first be personalized
to set up several registers and load in the appropriate passwords and keys. This is
accomplished through programming the configuration memory of CryptoMemory using
simple write and read commands. To gain access to the configuration memory, the
secure code must first be successfully presented. For the AT88SC0204C device, the
secure code is $E5 47 47. After writing and verifying data in the configuration memory,
the security fuses must be blown to lock this information in the device. For additional
information on personalizing CryptoMemory, please see the application notes Program-
ming CryptoMemory for Embedded Applications and Initializing CryptoMemory for
Smart Card Applications (at www.Atmel.com).
2022HS–SMEM–04/07