AN2284 datasheet(19/40 Pages) STMICROELECTRONICS

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AN2284

7 ISO 7816-3 - Electronic Signal and Transmission Protocol

19/40

7.1

ISO 7816-4 - Smart Card Commands

The previous chapter discussed the answer-to-reset (ATR) mechanism, which establishes a

basic communication channel between the smart card and the reader. This channel is a half-

duplex physical channel. This chapter investigates the use of more complex protocols on top of

this physical channel.

A link-level communication protocol resides directly on top of the physical channel, providing

error-free communication between the reader and the smart card. Once this link level protocol

is established, application-level protocols can be defined. ISO 7816-4 defines two such

application-level protocols:

●

File system API providing a set of functions to manipulate files (e.g. read, write, select etc.)

●

Security service API allowing the smart card and the reader to mutually authenticate

themselves and also to encrypt data to be exchanged between the card and the reader.

ISO 7816-4 defines a protocol message structure to support the application protocol APIs. This

message structure consists of application protocol data units (APDUs) which are exchanged

between the reader application and the smart card application by the link level protocol. This

chapter will provide an overview of the file access and security APIs. A more detailed

description can be found in Appendix A, "The ISO 7816-4 Command set".

7.1.1

The T0 Protocol

The T=0 protocol is a byte-oriented protocol where a character is transmitted across the

channel between the reader and the card. In addition, error handling is performed on each byte

by looking at the parity bit. If the actual parity bit does not correspond to the parity of the

transmitted data, then an error must have occurred. In the T=0 protocol, the receiving side

signals that it requires the byte to be retransmitted in the case of detecting a parity error. This is

done by holding the I/O line low (normally the I/O line is set high preceding the transfer of a

byte). When the transmitting side detects this, it resends the byte that was previously received

in error.

The reader and the smart card exchange data structures known as transmission protocol data

units (TPDUs). It consists of two distinct structures:

●

a command that is sent from the reader to the card

●

a response that is sent from the card to the reader

The command header includes the following five fields each of one byte in length:

●

CLA: class designation of the command set to establish a collection of instructions

●

INS: specifies a specific instruction from within the set of instructions

●

P1: used to specify the addressing used by the [CLA, INS] instruction

●

P2: also used to specify the addressing used by the [CLA, INS] instruction

●

P3: specifies the number of data bytes transferred to or from the card as part of the [CLA,

INS] instruction execution.

Each value of CLA defines an application-specific set of instructions. Table 5. below lists values

for some sets of instructions.

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