PCF7936AS datasheet(20/32 Pages) PHILIPS

20 / 32 page

NXP Semiconductors

Product Specification

Security Transponder (HITAG2)

PCF7936AS

2010 May 04

CONFIDENTIAL

7.4 Calculation Unit

The PCF7936AS incorporates a Calculation Unit for use

during mutual device authentication, command operation

and EEPROM data exchange, if the device is configured

for Cipher mode. The security algorithm involves a quasi

unique 32 bit Identifier, a 48 bit Secret Key and a 32 bit

Random Number.

The Identifier and the Secret Key are stored in the

Transponder Memory, TM. The Identifier (IDE) is a factory

programmed quasi unique pattern, while the Secret Key is

initialized and subsequently locked by the customer during

device personalization.

Mutual authentication of the Security Transponder in Cipher

mode is triggered by means of the START_AUTH

command, see also section 7.3. As a result, the device

reveals

its

Identifier

the

interrogating

system

(basestation) and subsequently the interrogating system

has to send a 32 bit Random Number and a ciphered

Signature to the device. Both are processed by the

Calculation Unit, involving the Secret Key (SK) and

Identifier (IDE), in order to authenticate the interrogating

system. If successful, the device replies with a ciphered

response for validation by the interrogating system.

Details concerning the security algorithm implementation

are specified in a separate Application Note. Please contact

your local NXP representative for more information.

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