AT88SC0808C-SI データシートの表示（PDF） - Atmel Corporation

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AT88SC0808C-SI

8 x 128 x 8 CryptoMemory™

Atmel Corporation 

AT88SC0808C

Password Verification

Passwords may be used to protect read and/or write access of any user zone. When a

valid password is presented, it is memorized and active until power is turned off, unless

a new password is presented or RST becomes active. There are eight password sets

that may be used to protect any user zone. Only one password is active at a time, but

write passwords give read access also.

Authentication Protocol

The access to a user zone may be protected by an authentication protocol. Any one of

four keys may be selected to use with a user zone.

The authentication success is memorized and active as long as the chip is powered,

unless a new authentication is initialized or RST becomes active. If the new authentica-

tion request is not validated, the card loses its previous authentication and it should be

presented again. Only the last request is memorized.

Note:

Password and authentication may be presented at any time and in any order. If the trials

limit has been reached (after four consecutive incorrect attempts), the password verifica-

tion or authentication process will not be taken into account.

Figure 4. Password and Authentication Operations

Checksum

2024BS–SMEM–10/02

VERIFY RPW

DATA

Checksum (CS)

VERIFY CS

VERIFY CS

CS

Write DATA

The AT88SC0808C 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 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 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.

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