HCS412_11 datasheet(25/52 Pages) MICROCHIP

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DS41099D-page 25

HCS412

FIGURE 4-9:

PROGRAM SEQUENCE - CONSECUTIVE WORDS

FIGURE 4-10: PROGRAMMING - VERIFICATION

4.3.6

IFF CHALLENGE AND RESPONSE

The transponder reader sends one of four possible IFF

commands indicating which crypt key and which algo-

rithm to use to encrypt the challenge (Table 4-7).

The command is followed by the 32-bit challenge, typi-

cally a random number. The HCS412 encrypts the

challenge using the designated crypt key and algorithm

and responds with the 32-bit encrypted result. The

reader authenticates the response by comparing it to

the expected value.

The second crypt key and the seed value occupy the

same EEPROM storage area. To use the second crypt

key for IFF, the Seed Enable (SEED) and the Tempo-

rary Seed Enable (TMPSD) configuration options must

be disabled.

TABLE 4-7:

CHALLENGE AND RESPONSE COMMANDS

Communication from reader to HCS412

Communication from HCS412 to reader

Write 18x16-bit

words total.

Start

Verify

Communication from reader to HCS412

Communication from HCS412 to reader

Write 18x16-bit

words total.

Verify 18x16-bit

words total.

01b Preamble

Start

1 LFTE

16-bit

Response

3LFTE Delay between

each 16-bit word

Approximately 1ms

delay before verify

begins.

Note: If seed transmissions are not appropriately

disabled, the HCS412 will default to using

KEY1 for IFF.

Command

Description

Expected data In

Response

10000

IFF using key-1 and IFF algorithm

32-Bit Challenge

32-Bit Response

10001

IFF using key-1 and HOP algorithm

32-Bit Challenge

32-Bit Response

10100

IFF using key-2 and IFF algorithm

32-Bit Challenge

32-Bit Response

10101

IFF using key-2 and HOP algorithm

32-Bit Challenge

32-Bit Response

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