isl6296a Intersil Corporation, isl6296a Datasheet - Page 8

• Manufacturer Part Number: isl6296a
• Description: Flexihash? For Battery Authentication
• Manufacturer: Intersil Corporation

match up, the device is a fake device and the host may shut
itself down. The flow chart in Figure 6 summarizes the
process that the host needs to execute.
It is recommended that device authentication be done once
in a while to maximize its effectiveness. Before a new
challenge code can be accepted by the device, the SESL
register must be re-written again to ensure that the original
seeds are re-loaded from the OTP ROM into the hash
engine prior to performing the next authentication code
calculation. Failure to follow the sequence will result is a bus
error, causing the sBER flag to be set in the STAT register.
SET-UP FOR DEVICE AUTHENTICATION SUPPORT
To configure the host and the ISL6296A to support device
authentication function, the pack manufacturer will need to
select at least 2 sets of 32-bit secret codes. For greater
security, a third set of 32-bit secret may be used. The
FlexiHash™ engine requires two sets of 32-bit secrets for
use in its hash calculation; the first set to define its hash
function, and the second set to initialize its seed for hash
calculation. These two sets can be selected from the same
secret location. The chosen secret codes are to be kept by
the pack manufacturer and maintained at utmost
confidentiality.
After the secrets have been determined, they are written into
the device’s OTP ROM. After verification that the codes have
been written in correctly, the relevant secrets lock-out bits at
ROM address location 0-00 should be set. Once set, the
lock-out bits can no longer be cleared. Thereafter, read/write
access to the secret information will no longer be possible,
and the secret codes are made available only to the
FlexiHash™ engine for generation of authentication code
based on a challenge code input from the host.
On the host side, the same secret codes will need to be kept,
and the same FlexiHash™ engine will have to be
implemented in firmware. Refer to the Application Note
AN1166 for detailed information of firmware implementation.
It is important that the secret codes be stored scrambled in
the host’s non-volatile memory so that the secret information
cannot be easily revealed by monitoring signal transfer on
the host PCB.
32-BIT HASH FUNCTION
FIGURE 5. AUTHENTICATION PROCESS FLOW DIAGRAM
32-BIT HASH SEED
64-BIT SECRET
8
FLEXIHASH
ENGINE
CHALLENGE WORD FROM HOST
32-BIT PSEUDO-RANDOM
8-BIT AUTHENTICATION
CODE
ISL6296A
THE HASH ENGINE
The hash engine consists of 4 separate programmable 8-bit
CRC calculators. Two sets of 32-bit secret codes are use by
the hash engine for authentication code generation. The first
set is used to define the CRC polynomial as well as the input
selection for each of the CRC calculators. The second is
used as initial seeds for the CRC calculations. Outputs of the
4 CRC calculators are logically combined to produce the
8-Bit output of the overall FlexiHash™ engine. The Block
Diagram of the FlexiHash engine is illustrated in Figure 7.
More detailed description on the hash engine can be found
in Application Note AN1166.
FIGURE 6. FLOW CHART FOR AUTHENTICATION PROCESS
SELECT HASH FUNCTION AND SEED
CHALLENGE TO CHLG REGISTER
BY WRITING TO SESL REGISTER
RESULT FROM AUTH REGISTER,
BASED ON THE SAME SECRETS
READ THE AUTHENTICATION
WAKE UP ISL6296A USING A
CALCULATE THE EXPECTED
THE TWO RESULTS MATCH?
AFTER WAITING FOR 1 BT
AUTHENTICATION RESULT
REGULAR BREAK SIGNAL
SEND A 32-BIT RANDOM
YES
START
END
D
THE SYSTEM
SHUT DOWN
NO
October 31, 2007
FN6567.0