ib technology

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Access Condition for Sector Trailer Block

The read/write access to the Keys and the Access Bits themselves is controlled by the access

conditions for the Sector Trailer Block. The read/write access is specified as “Never”,

“KeyA”, KeyB” or Key A|B (KeyA OR KeyB).

Access Bits

Access condition for:

KEY A

ACCESS BITS

KEY B

C1 C2 C3

Read Write

Read Write

Read Write

0

0

0

never keyA

keyA

never

keyA keyA

(KeyB can be read)

0

0

1

never keyA

keyA

keyA

keyA keyA

(Transport setting)

0

1

0

never never

keyA never

keyA never

(KeyB can be read)

0

1

1

never keyB

keyA|B keyB

never keyB

1

0

0

never keyB

keyA|B never

never keyB

1

0

1

never never

keyA|B keyB

never never

1

1

0

never never

keyA|B never

never never

1

1

1

never never

keyA|B never

never never

The new Mifare cards have the access conditions predefined as transport configuration:

C1 C2 C3 = (0 0 1) which means Sector Trailer Block can only be read or written to using

KeyA and KeyA itself can never be read.

Because the Access Bits themselves can be locked great care must be taken when any of these

settings are changed because they may be irreversible making the card unusable.

Access Condition for data areas

The read/write access to the data areas is also controlled by the access conditions defined in

the Sector Trailer Block. The read/write access is specified as “Never”, “KeyA”, KeyB” or

Key A|B (KeyA OR KeyB).

A data block can be a “read/write block” or a “value block”. For a “read/write” block the

basic read and write operations are allowed. For the “value block” the additional increment,

decrement, transfer and restore operations can apply. In one case (001) only read and

decrement are possible for a “non-rechargeable” card application and in another case (110)

recharging is only possible using keyB.

The default transport configuration specifies that the data areas can only be accessed using

KeyA|B, however the operation of the Mifare cards define that “IF KEYB CAN BE READ

IN THE CORRESPONDING SECTOR TRAILER THEN IT CANNOT SERVE FOR

AUTHENTICATION”. This means that for the transport configuration (and 001 and 010

cases), KeyA must be used for access.

Note also that the read-only status of the Manufacturer Block is not affected by the access bits

setting.