PCF7936AS datasheet(18/32 Pages) PHILIPS

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NXP Semiconductors

Product Specification

Security Transponder (HITAG2)

PCF7936AS

2010 May 04

CONFIDENTIAL

START_AUTH (Cipher Mode)

If configured for Cipher mode, START_AUTH triggers the

mutual device authentication sequence. If completed

successfully, the device enters AUTHORIZED state and

subsequently supports ciphered read and write access of

the Transponder Memory, TM. Device authentication

employs the Identifier, a Random Number, a ciphered

Signature and a ciphered device Response, see Figure 13.

After acceptance of the 5 bit command sequence, the initial

device Response consist of the 32 bit Identifier (IDE) that is

stored in the Transponder Memory. Subsequently, the

interrogating system (e.g. basestation) has to identify itself

towards the device, by issuing a 32 bit Random Number

and a matching 32 bit ciphered Signature. The device

verifies the authenticity of the ciphered Signature received,

by means of the Calculation Unit, involving the Secret Key

(SK). If successful, the final device Response consists of

the

ciphered

content

page 3

that

contains

the

Transponder and Memory configuration (TMCF) and device

Password Transponder (PSW T). The MSB is send first.

In case the authentication process fails, an error condition

occurs that causes the device to terminate the command

and to enter WAIT state. The device will send no further

Response in this case.

Subsequent commands may be issued after termination of

the final tWAIT,Bs.

For proper command execution, the interrogating system

has to identify itself towards the device within the specified

IDLE time, otherwise the device may generate a power-on

reset condition, upon which the circuitry would be reset and

the transponder initialized, causing the device to enter the

WAIT state.

The Security Algorithm details, involved in the process of

mutual device authentication, are specified in a separate

Application Note. Please contact your NXP representative

for more information.

SEND to

Transponder

RECEIVED from

Transponder

1 1 1 1 1

tWAIT,Tr

IDE

tWAIT,Bs

1 1 0 0 0

CM[4:0]

START_AUTH

bit 31 ..............bit 0

tWAIT,Bs

bit 31 ..............bit 0

Random Number

bit 31 ..............bit 0

[Signature]CIPHER

bit 31 ..............bit 0

tWAIT,Tr

[Page 3 Block 0]CIPHER

1 1 1 1 1

tIDLE

SEND to

Transponder

RECEIVED from

Transponder

Figure 14. START_AUTH timing

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