Mifare DESFire

Implementation Approach
On a Mifare Classic Platform it is only practical to store application data in a single memory structure with the same access conditions for all items. Mifare Classic also has no integral filing system therefore data can only be stored and referenced by its actual location in memory. Below is a block of memory containing a CCDA service within a Constructed Data Object (CDO). The absolute address of this service is known from the Services Directory on the Mifare card.

Block Data
128 E0 45 50 05 00 43 43 44 41 DF 23 09 01 63 37 10
129 00 00 04 13 01 DF 32 0A 00 46 72 65 64 65 72 69
130 63 6B DF 33 08 00 59 65 75 6C 65 74 74 5F 2B 05
131 02 19 39 05 16 DF 56 03 00 32 34 DF 57 09 00 50
132 45 31 35 20 39 4C 58 C0 02 FB 15 00 00 00 00 00
133 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
134 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
135 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

This structure is described fully in document [6], the Mifare 4k specification.
Because of these constraints only certain kinds of citizen data are deemed
suitable for storage on a Mifare Classic platform. At the other end of the scale document [5] describes how citizen data is stored on a processor card such as a JCOP31. The power and size of these platforms allows for sophisticated filing and security systems as well as other desirable features such as garbage collection whereby memory occupied by deleted items can be recovered. It is also possible to store individual data items within a service in individual files with their own access requirements.
Each service application contains two mandatory files. These files are the Index file, and the Free Access file. The Index file stores the location and display description of all data items held by the service application. The Free Access file contains all the data items which are freely readable. All other data items are held in EF files with their individual access conditions.

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Figure 1. Service Application Contents on Javacards

In terms of capability, the DESFire® platforms lie somewhere in between the two. Although the DESFire® is still essentially a memory card, the filing system and enhanced security features allow for a more flexible file-based approach. However, the relatively limited memory sizes and lack of garbage collection facilities mean that a full implementation along javacard lines is impractical. What is therefore proposed is an optimised version better suited to the memory limitations of the DESFire®. It is important to remember that whatever the means of access or storage the service USIDs, data tags and formats described in document [4] are consistent across all the LASSeO platform specifications.

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Figure 2. The LASSeO Family of Specifications