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AT88SC153

1016D–SMEM–04/04

In the write lock configuration, only one byte of the page can be written at a time. Even if

several bytes are received, only the first byte will be taken into account by the device.

Password Verification

Compare the operation password presented with the stored one, and write a new bit in

the corresponding attempts counter for each wrong attempt. A valid attempt erases the

attempts counter and allows the operation to be carried out as long as the chip is

powered.

The current password is memorized and active until power is turned off, unless a new

password is presented or RST becomes active. Only one password is active at a time.

The AT88SC153 requires that the Verify Password command be transmitted twice in

sequence to successfully verify a write or read password. (This two-pass method of

password verification was implemented in the AT88SC153 to protect the device from

attacks on the password security system.) The first Verify Password command can be

considered an initialization command. It will write a new bit (“0”) in the corresponding

PAC. The data bits in this initialization command are ignored. The second Verify Pass-

word c om m and wi ll co m p ar e th e 3- byte password dat a prese nted wi th the

corresponding password value stored in memory. If the comparison is valid, the PAC will

be cleared. A successful password verification will allow authorized operations to be

carried out as long as the chip is powered. The current password is memorized and

active until power is turned off, a new password is presented, or RST becomes active.

Only one password is active at a time. If a new user zone is selected that points to a dif-

ferent password set, the new password must be verified and the old password becomes

invalid.

Authentication Protocol

The access to an user zone may be protected by an authentication protocol in addition

to password-dependent rights.

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 has lost its previous authentication and it should

be presented again. Only the last request is memorized.

The authentication verification protocol requires the host to perform an Initialize Authen-

tication command, followed by a Verify Authentication command.

The password and authentication may be presented at any time and in any order. If the

trials limit has been reached, i.e., the 8 bits of the attempts counter have been written,

the password verification or authentication process will not be taken into account.