The Architecture of Electronic Data Carriers - RFID: Fundamentals and Applications in Contactless Smart Cards and Identification - page 277

P

Security
encoding

Appl. X
(planned)

Appl. Y
(planned)

RFU RFU

RFU RFU RFU RFU

RFU RFU RFU RFU

Figure 10.14 Several applications on one transponder — each protected by its own secret key

Key/Acc/Len 1

Segment 1

Key/Acc 1

Segment 1

Segment 2

Key/Acc 2

Key/Acc/Len 2

Segment 3

Segment 2

Key/Acc 3

Fixed segmentation Free (variable) segmentation

Figure 10.15 Differentiation between fixed segmentation and free segmentation

the requirements of the application using the memory area. Because of the difficulty in
realising variable segmentation , this variant is rare in transponders with state machines.
Figure 10.16 illustrates the memory configuration of a transponder with fixed seg-
mentation. The available memory, totalling 128 bytes, is divided into four segments,
known as 'pages'. Each of the four segments can be protected against unauthorised
reading or writing by its own password. The access register of this transponder ('OTP
write protection') consists of an additional memory area of 16 bits per segment. Delet-
ing a single bit from the access register permanently protects 16 bits of the application
memory against overwriting.