AT88SC25616C-MP View Datasheet(PDF) - Atmel Corporation

Part Name

Description

Manufacturer

AT88SC25616C-MP

CryptoMemory 256 Kbit

Atmel Corporation 

Checksum

The AT88SC25616C implements a data validity check function in the form of a checksum, 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 a 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 pro-

vides a bidirectional data integrity check and data origin authentication capability in the form of a

Message Authentication Code (MAC). Only the host/device that carried out a valid authentica-

tion 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 authentication and/or encryption activation will be required to reacti-

vate the MAC.

Encryption

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 configura-

tion 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.

Supervisor Mode 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.

Modify Forbidden 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.

Program Only

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”.

Initial Device

Programming

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 com-

mands. To gain access to the configuration memory, the secure code must first be successfully

presented. For the AT88SC25616C device, the secure code is $17 C3 3A. After writing and ver-

ifying 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 appli-

cation notes Programming CryptoMemory for Embedded Applications and Initializing

CryptoMemory for Smart Card Applications (at www.Atmel.com).

12 AT88SC25616C

5017HS–SMEM–11/08

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