AT88SC0404C-PU Просмотр технического описания (PDF) - Atmel Corporation

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AT88SC0404C-PU

CryptoMemory® 4 Kbit

Atmel Corporation 

AT88SC0404C

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

2023ES–SMEM–07/04

VERIFY RPW

DATA

Checksum (CS)

VERIFY CS

VERIFY CS

CS

Write DATA

The AT88SC0404C 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.

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