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7 ISO 7816-3 - Electronic Signal and Transmission Protocol

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called SW1 and SW2. These fields return a status code in which one byte is used to specify an

error category and the other is used to specify a command-specific status or error indication.

7.2.2

The File System API

The file system is used on the nonvolatile memory or EEPROM. It is defined as a simple

hierarchical structure (similar to conventional file systems). The file system may contain three

types of files (identified by a 2-byte identifier):

●

Master file (MF)

●

Dedicated file (DF)

●

Elementary file (EF)

There is one master file found on each smart card and it is the root of the file system. A master

file may contain dedicated files or elementary files. The file identifier reserved for the master file

is 3F00. The directory file is essentially a container (or directory) for elementary files - a DF may

contain zero or more EFs. Dedicated files partition the smart card into an ordered structure of

elementary files. A dedicated file must be given a unique file identifier within the dedicated file

or master file that contains it - allowing for a unique path for each file. A dedicated file can also

be referenced by name (1-16 bytes long). The naming convention can be found in ISO 7816-5.

An elementary file is a leaf node in the hierarchy and contains the actual data. An elementary

file can be identified by a 5-bit identifier within a dedicated file. This file system hierarchy is

illustrated in Figure 9.

Figure 9.

The Smart Card File System Architecture

There are four types of elementary files:

●

Transparent file

●

Linear, fixed-length record file

●

Linear, variable-length record file

●

Cyclic, fixed-length record file

A transparent file is essentially a string of bytes i.e. an unstructured binary file. Consequently a

byte offset from the start of the file is required when data is to be read or written to this type of

file. In addition, a command to read or write to a transparent file will contain the length of the

byte string to be read or written to the file.