AT88SC0404C ATMEL Corporation, AT88SC0404C Datasheet - Page 7

• Manufacturer Part Number: AT88SC0404C
• Description: CryptoMemory 4 Kbit
• Manufacturer: ATMEL Corporation

Password Verification
Authentication Protocol
Checksum
2023ES–SMEM–07/04
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.
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:
Figure 4. Password and Authentication Operations
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.
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.
Checksum (CS)
VERIFY RPW
VERIFY CS
Write DATA
DATA
VERIFY CS
CS
AT88SC0404C
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