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PCF7936AS/3851/C,1

Security Transponder (HITAG2)

NXP Semiconductors. 

NXP Semiconductors

Security Transponder (HITAG2)

Product Specification

PCF7936AS

7.1.3 Secret Key, SK

The Secret Key, SK is applicable in Cipher mode only

(ENC = 1). The Secret Key is a 48 bit pattern, which

typically is initialized and subsequently locked by the

customer during device personalization. The Secret Key is

located in page 1 and 2, see Figure 4.

The 32 least significant bits of SK (bit 31 to bit 0) are

located in page 1 while the 16 most significant bits (bit 47 to

bit 32) are located in page 2 at bit address 0 to 15.

The Immobilizer Secret Key is incorporated in the process

of device authentication and used by the on-chip

calculation unit as well as by the interrogating system.

However the Immobilizer Secret Key is never transmitted

during the process of device authentication. For details

refer to section 7.3.1, START_AUTH command.

The Secret Key may be assigned any value that is

considered useful by the application. The SK can be

protected against reading and writing by setting the lock bit

SKL, see section 7.1.4

7.1.4 Transponder and Memory Configuration, TMCF

Access to the Transponder Memory, TM, and device

configuration is controlled by a set of configuration bits,

TMCF, located in page 3, see Figure 6.

bit 31 30 29 28 27 26 25 24

TMCF

MSB

LSB

Figure 6. Transponder Memory Configuration, TMCF

The memory access rights applied by TMCF affect the

behavior of READ_PAGE and WRITE_PAGE commands

only. Device operation, e.g. with respect to the

authentication process, is not affected at all.

Secret Key Lock, SKL

If set, the Password Basestation, PSW B, (Password

mode) or the Secret Key, SK, (Cipher mode) is irreversible

locked against reading and writing (OTP like). If set once,

its value can no longer be read or altered.

Page 3 Lock, PG3L

If set, page 3 is irreversible locked against writing (OTP

like). Thus if set once, the Transponder and Memory

Configuration (TMCF) as well as the Password

Transponder (PSW T) can no longer be altered. However,

reading is supported in any case.

Protect Write User Page 4 and 5, PWP1

If set, a write protection is assigned for the user pages

page 4 and 5 (USER0 and USER1). As a result its content

cannot be altered, however, reading is supported in any

case.

If cleared, page 4 and page 5 support reading and writing.

The content and organization of the user pages is fully

determined by the application.

Protect Write User Page 6 and 7, PWP0

If set, a write protection is assigned for the user pages

page 6 and 7 (USER2 and USER3). As a result its content

cannot be altered, however, reading is supported in any

case.

If cleared, page 6 and page 7 support reading and writing.

The content and organization of the user pages is fully

determined by the application.

Enable Cipher Mode, ENC

The device may be configured for to perform authentication

in either Password mode or Cipher mode.

If ENC is set, Cipher mode is selected, otherwise Password

mode.

Thus, ENC affects operation of the START_AUTH

command and whether plain or ciphered transmission of

data and commands is supported, for details refer to

section 7.3.1.

2010 May 04

9

CONFIDENTIAL

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