13

AT88SC153

1016D–SMEM–04/04

Initialize Authentication

Figure 10. Initiatize Authentication

Note:

Q: Host random number, 8 bytes

The Initialize Authentication command sets up the random generator with the crypto-

gram (Ci), the secret seed (Gc), and the host random number (Q). Once the sequence is

completed and a stop condition is issued, there is a nonvolatile write cycle to clear a

new bit of the AAC. In order to complete the authentication protocol, the device requires

the host to perform an ACK polling sequence with the specific command byte of $B6,

corresponding to the Verify Authentication command.

Verify Authentication

Figure 11. Verify Authentication

Note:

Q1: Host challenge, 8 bytes

If Q1 is equal to Ci + 1, then the device writes Ci + 2 in memory in place of Ci; this must

be preceded by the Initialize Authentication command. Once the sequence is completed

and a stop condition is issued, there is a nonvolatile write cycle to update the associated

attempts counter. In order to know whether or not the authentication was correct, the

device requires the host to perform an ACK polling sequence with the specific command

byte of $BD, to read the corresponding attempts counter in the configuration zone. A

valid authentication will result in the AAC cleared to $FF. An invalid authentication

attempt will initiate a nonvolatile write cycle, but no clear operation will be performed on

the AAC.

Device Operation

Clock and Data

Transitions

The SDA pin is normally pulled high with an external device. Data on the SDA pin may

change only during SCL-low time periods (Figure 13 on page 14). Data changes during

SCL-high time periods will indicate a start or stop condition as defined below.

Start Condition

A high-to-low transition of SDA with SCL high is a start condition that must precede any

other command (Figure 12 on page 14).

Q1(7)

Q1(1)

Q1(0)

1