ISO 7816-4: Interindustry Commands for Interchange

5. Basic Organizations

5.1 Data structures 
5.2 Security architecture of the card 
5.3 APDU message structure 
5.4 Coding conventions for command headers, data fields and response trailers 
5.5 Logical channels 
5.6 Secure messaging

5.1 Data structures

This clause contains information on the logical structure of data as seen at the interface, when processing interindustry commands for interchange. The actual storage location of data and structural information beyond what is described in this clause are outside the scope of ISO/IEC 7816.

5.1.1 File organization 
5.1.2 File referencing methods 
5.1.3 Elementary file structures 
5.1.4 Data referencing methods 
5.1.4.1 Record referencing 
5.1.4.2 Data unit referencing 
5.1.4.3 Data object referencing 
5.1.5 File control information

5.1.1 File organization

This part of ISO/IEC 7816 supports the following two categories of files :

• Dedicated file (DF)
• Elementary file (EF)

The logical organization of data in a card consists of following structural hierachy of dedicated files :

• The DF at the root is called the master file (MF). The MF is mandatory.
• The other DFs are optional.

The following two types of EFs are defined :

• Internal EF - Those EFs are intended for storing data interpreted by the card, i.e. data analyzed and used by the card for management and control purposes.
• Working EF - Those EFs are intended for storing data not interpreted by the card, i.e. data to be used by the outside world exclusively.

Figure 1 illustrates an example of the logical file organization in a card. 

Figure 1 - Logical file organization (example)

 

5.1.2 File referencing methods

When a file cannot be implicitly selected, it shall be possible to select it by at least one of the following methods :

• Referencing by file identifier - Any file may be referenced by a file identifier coded on 2 bytes. If the MF referenced by a file identifier, '3F00' shall be used (reserved value). The value 'FFFF' is reserved for future use. The value '3FFF' is reserved (see referencing by path). In order to select unambiguously any file by its identifier, all EFs and DFs immediately under a given DF shall have different file identifiers.
• Referencing by path - Any file may be referenced by a path (concatentation of file identifiers). The path begins with the identifier of the MF or of the current DF and ends with the identifier of the file itself. Between those two identifiers, the path consists of the identifiers of the successive parent DFs if any. The order of the file identifiers is always in the direction parent to child. If the identifier of the current DF is not known, the value '3FFF' (reserved value) can be used at the beginning of the path. The path allows an unambiguous selection af any file from the MF or from the current DF.
• Referencing by short EF identifier - Any EF may be referenced by a short EF identifier coded on 5 bits valued in the range from 1 to 30. The value '0' used as a short EF identifier references the currently selected EF. Short EF identifiers connot be used in a path or as a file identifier (e.g. in a SELECT FILE command).
• Referencing by DF name - Any DF may be referenced by a DF name coded on 1 to 16 bytes. In order to select unambiguously by DF name (e.g. when selecting by means of application identifiers as define in part 5 of ISO/IES 7816), each DF name shall be unique within a given card.

5.1.3 Elementary file structures

The following structures of EFs are defined :

• Transparent structure - The EF is seen at the interface as a sequence of data units.
• Record structure - The EF is seen at the interface as a sequence of individually identifiable records.

The following attributes are defined for EFs structured in records :

• Size of the records: either fixed or variable
• Organization of the records: either as a sequence (linear structure) or as a ring (cyclic structure).

The card shall support at least one of the following four methods for structuring EFs :

• Transparent EF.
• Linear EF with record of fixed size.
• Linear file with records of variable size.
• Cyclic EF with records of fixed size.

Figure 2 shows those for EF structures.

F I G U R E 2

Figure 2 - EF structures

NOTE - The arrow on the figure references the most recently written record.

5.1.4 Data referencing methods

Data may be referenced as records, as data units or as data objects. Data is considered to be stored in a single continuous sequence of records (within an EF of record structure) or of data units (within an EF of transparent structure). Reference to a record or to a data unit outside an EF is an error. 
Data referencing method, record numbering method and data unit size are EF-dependent features. The card can provide indications in the ATR, in the ATR file and in any file control information. When the card provides indications in several places, the indication valid for a given EF is the closest one to that EF within the path from the MF to that EF.

5.1.4.1 Record referencing

Within each EF of record structure, each record can be referenced by a record identifier and/or by a record number. Record identifiers and record numbers are unsigned 8-bit integers with values in the range from '01' to 'FE'. The value '00' is reserved for special purposes. The value 'FF' is RFU. 
Referencing by record identifier shall induce the management of a record pointer. A reset of the card, a SELECT FILE and any command carrying a valid short EF identifier can affect the record pointer. Referencing by record number shall not affect the record pointer.

Referencing by record identifier - Each record identifier is provided by an application. If a record is a SIMPLE-TLV data object in the data field for a message (see 1.4.4), then the record identifier is the first byte of the data object. Within an EF of record structure, records may have the same record identifier, in which case data contained in the records may be used for discriminating between them. 
Each time a reference is made with a record identifier, an indication shall specify the logical position of the target record the first or last occurrence, the next or previous occurrence relative to the record pointer :

• Within each EF of linear structure, the logical positions shall be sequentially assigned when writing or appending i.e. in the order of creation. Therefore the first created record is in the first logical position.
• Within each EF of cyclic structure, the logical positions shall be sequentially assigned in the opposite order, i.e. the most recently created record is in the first logical position.

Each time a reference is made with a record identifier, an indication shall specify the logical position of the target record the first or last occurrence, the next or previous occurrence relative to the record pointer :

• Within each EF of linear structure, the logical positions shall be sequentially assigned when writing or appending i.e. in the order of creation. Therefore the first created record is in the first logical position.
• Within each EF of cyclic structure, the logical positions shall be sequentially assigned in the opposite order, i.e. the most recently created record is in the first logical position.

The following additional rules are defined for linear structures and for cyclic structures :

• The first occurrence shall be the record with the specified identifier and in the first logical position; the last occurrence shall be the record with the specified identifier and in the last logical position.
• When there is no current record, the next occurrence shall be equivalent to the first occurrence. The previous occurrence shall be equvalent to the last occurrence.
• When there is a current record, the next occurrence shall be the closest record with the specified identifier but in a greater logical position than the current record. The previous occurrence shall be the closest record with the specified identifier but in a smaller logical position than the current record.
• The value '00' shall refer to the first, last, next and previous record in the numbering sequence, independently from the record identifier.

Referencing by record number - Within each EF of record structure, the record numbers are unique and sequential :

• Within each EF of linear structure, the record numbers shall be sequentially assigned when writing or appending, i.e. in the order of creation. Therefore the first record (record number one, #1) is the first created record.
• Within each EF of cyclic structure, the record numbers shall be sequentially assigned in the opposite order, i.e. the first record (record number one, #1) is the most recently created record.

The following additional rule is defined for linear structures and for cyclic structures :

• The value '00' shall refer to the current record, i.e. that record fixed by the record pointer.

5.1.4.2 Data unit referencing

Within each EF of transparent structure, each data unit can be referenced by an offset (e.g. in READ BINARY command). It is an unsigned integer, limited to either 8 or 15 bits according to an option in the respective command. Valued to 0 for the first data unit of the EF, the offeset is incremented by 1 for every subsequent data unit. 
By default, i.e. if the card gives no indication, the size of the date unit is one byte.

NOTES

1. An EF of record structure may support data unit referencing and in case it does, data units may contain structural information along with data, e.g. record numbers in a linear structure.
2. Within an EF of record structure, data unit referencing may not provide the intended result because the storage order of the records in the EF is not known, e.g. storage order in a cyclic structure.

5.1.4.3 Data object referencing

Each data object (as defined in 1.4.4) is headed by a tag which references it. Tags are specified in this part and other parts of ISO/IEC 7816.

5.1.5 File control information

The file control information (FCI) is the string of data bytes available in response to a SELECT FILE command. The file control information may be present for any file. Table 1 introduces 3 templates intended for conveying file control information when coded as BER-TLV data objects.

• The FCP template is intended for conveying file control parameters (FCP), i.e. any BER-TLV data objects defined in table 2.
• The FMD template is intended for conveying file management data (FMD), i.e. BER-TLV data objects specified in other clauses of this part or in other parts of ISO/IEC 7816 (e.g., application label as defined in part 5 and application expiration data as defined in part 6).
• The FCI template is intended for conveying file control parameters and file management data.

Tag	Values
'62'	File control parameters (FCP template)
'64'	File management data (FMD template)
'6F'	File control information (FCI template)

Table 1 - Template relevant to FCI

The 3 templates may be retrieved according to selection options of the SELECT FILE command . If the FCP or FMD option is set, then the use of the corresponding template is mandatory. If the FCI option is set then the use of the FCI template is optional.

Part of the file control information may additionally be present in a working EF under control of an application and referenced under tag '87'. The use of the FCP or FCI template is mandatory for the coding of file control information in such an EF.

File control information not coded according to this part of ISO/IEC 7816 may be introduced as follows :

• '00' or any value higher then '9F' - The coding of the subsequent string of bytes is proprietary.
• Tag='53' - The value field of the data object consists of discretionary data not coded in TLV.
• Tag='73' - The value field of the data object consists of dicretionary BER-TLV data object.

Table 2 - File control parameters

Tag	L	Value	Applies to
'80'	2	Number of data bytes in the file, excluding structural information.	Transparent EFs
'81'	2	Number of data bytes in the file, including structural information if any	Any file
'82'	1	File descriptor byte (see table 3)	Any file
'82'	2	File descriptor byte followed by data coding byte (see table 86)	Any file
'82'	3 or 4	File descriptor byte followed by data coding byte and maximum record length.	EFs with record structure
'83'	2	File identifier	Any file
'84'	1 to 16	DF name	DFs
'85'	var.	Proprietary information	Any file
'86'	var.	Security attributes (coding outside the scope of this part of ISO/IEC 7816)	Any file
'87'	2	Identifier of an EF containing an extension of the FCI	Any file
'88' to '9E'		RFU
'9FXY'		RFU

Table 3 - File descriptor bytey

b8 b7 b6 b5 b4 b3 b2 b1	Meaning
0 x -- -- -- -- -- --	File accessibility
0 0 -- -- -- -- -- --	Not shareable file
0 1 -- -- -- -- -- --	Shareable file
0 -- x x x -- -- --	File type
0 -- 0 0 0 -- -- --	Working EF
0 -- 0 0 1 -- -- --	Internal EF
0 -- 0 1 0 -- -- --	Reserved
0 -- 0 1 1 -- -- --	for
0 -- 1 0 0 -- -- --	proprietary
0 -- 1 0 1 -- -- --	types
0 -- 1 1 0 -- -- --	of EFs
0 -- 1 1 1 -- -- --	DF
0 -- -- -- -- x x x	EF structure
0 -- -- -- -- 0 0 0	No information given
0 -- -- -- -- 0 0 1	Transparent
0 -- -- -- -- 0 1 0	Linear fixed, no further info
0 -- -- -- -- 0 1 1	Linear fixed SIMPLE-TLV
0 -- -- -- -- 1 0 0	Linear variable, no further info
0 -- -- -- -- 1 0 1	Linear variable SIMPLE-TLV
0 -- -- -- -- 1 1 0	Cyclic, no further info
0 -- -- -- -- 1 1 1	Cyclic, SIMPLE-TLV
1 x x x x x x x	RFU

Shareable means that the file supports at least concurrent access on different logical channels.

5.2 Security architecture of the card

This clause describes the following features :

5.2.1 Security status 
5.2.2 Security attributes 
5.2.3 Security mechanisms

Security attributes are compared with the security status to execute command and/or to access files. 

5.2.1 Security status

Security status represents the current state possibly achieved after completion of

• answer to reset (ATR) and possible protocol type selection (PTS) and/or
• a single command or a sequence of commands possibly performing authentication procedures.

The security status may also result from the completion of a security procedure related to the identification of the involved entities, if any, e.g.

• by proving the knowledge of a password (e.g. using a VERIFY command)
• by proving the knowledge of a key (e.g. using a GET CHALLANGE command followed by an EXTERNAL AUTHENTICATE command)
• by secure messaging (e.g. message authentication)

Three security statuses are considerd :

• Global security status - It may be modified by the completion of an MF-related authentication procedure (e.g. entity authentication by a password or by a key attached to the MF).
• File-specific security status - It may be modified by the completion of a DF-related authentication procedure (e.g. entity authentication by a password or by a key attached to the specific DF). It may be maintained, recovered or lost by file selection (see 6.10.2) this modification may be relevant only for the application to which the authentication procedure belongs.
• Command-specific status - It only exists during the execution of a command involving authentication using secure messaging (see 1.6): such a command may leave the other security status unchanged

If the concept of logical channels is applied, the file specify security status may depend on the logical channel (see 1.5.1).

5.2.2 Security attributes

The security attributes, when they exist, define the allowed actions and the procedures to be performed to complete such actions.

Security attibutes may be associated with each file and fix the security conditions that shall be satisfied to allow operations on the file. The security attributes of file depend on :

• its category (DF or EF),
• optional parameters in its file control information and/or in that of its parent file(s).

NOTE - Security attributes may also be associated to other objects (e.g. keys).

5.2.3 Security mechanisms

This part of ISO/IEC 7816 defines the following security mechanisms :

• Entity authentication with password - The card compares data received from the outside world with secret internal data. This mechanism may be used for protecting the right of the user.
• Entity authentication with key - The entity to be euthenticated has to prove the knowledge of the relevant key in an authentication procedure (e.g. using aGET CHALLENGE command followed by an EXTERNAL AUTHENTICATE command).
• Data authentication - Using internal data, either secret or public, the card checks redundant data recived from the outside world. Alternately, using secret internal data, the card computes a data element (cryptographic checksum or digital signature) and inserts it in the data sent to the outside world. This mechanism may be used for protecting the rights of a provider.
• Data encipherment - Using secret internal data, the card deciphers a cryptogram received in a data field. Alternately, using internal data, either secret or public, the card computes a cryptogram and inserts it in a data field, possibly together with other data. This mechanism may be used to provide a confidentiality service, e.g. for key management and conditional access. In addition to the cryptogram mechanism, data confidentiality can be achieved by data concealment. In this case, the card computes a string of concealing bytes and adds it by exclusive-or to data bytes received from or sent to the outside world. This mechanism may be used for protecting privacy and for reducing the possibilities of message filtering.

The result of an authentication may be logged in an internal EF according to the requrements of the application.

5.3 APDU message structure

A step in an application protocol consists of sending a command, processing it in the receiving entity and sending back the response. Therefore a spcecific response corresponds to a specific command, referred to as a command-response pair.

5.3.1 Command APDU 
5.3.2 Decoding convention for command bodies 
5.3.3 Response APDU

An application protocol data unit (APDU) contains either a command message or a response message, sent from the interface device to the card or conversely. 
In a command-response pair, the command message and the response message may contain data, thus inducing four cases which are summarised by table 4.

Table 4 - Data within a command-response pair

Case	Command data	Expected response data
1	No data	No data
2	No data	Data
3	Data	No data
4	Data	Data

5.3.1 Command APDU

Illustrated by figure 3 (see also table 6), the command APDU defined in this part of ISO/IEC 7816 consists of

• a mandatory header of 4 bytes (CLA INS P1 P2),
• a conditional body of variable length

Header	Body
CLA INS P1 P2	[Lc field] [Data field] [Le field]

Figure 3 - Command APDU structure

The number of bytes present in the data field of the command APDU is denoted by Lc.

The maximum number of bytes expected in the data field of the response APDU is denoted by Le (length of expected data). When the Le field contains only zeros, the maximum number of available data bytes is requested. 
Figure 4 shows the 4 structures of command APDUs according to the 4 cases defined in table 4.

I M A G E 4

Figure 4 - The 4 structures of command APDUs

In case 1, the length Lc is null; therefore the Lc field and the data field are empty. The length Le is also null; therefore the Le field is empty. Consequently, the body is empty. 
In case 2, the length Lc is null; therefore the Lc field and the data field are empty. The length of Le is not null; therefore the Le field is present. Consequently, the body consists of the Le field. 
In case 3, the length Lc is not null; therefore the Lc field is present and the data field consists of the Lc subsequent bytes. The length Le is null; therefore the Le field is empty. Consequently, the body consists of the Lc field followed by the data field. 
In case 4, the length Lc is not null; therefore the Lc field is present and the data field consists of the Lc subsequent bytes. The length Le is also not null; therefore the Le field is also present. Consequently, the body consists of the Lc field followed by the data field and the Le field.

5.3.2 Decoding conventions for command bodies

In case 1, the body of the command APDU is empty. Such a command APDU carries no length field.

In cases 2, 3 and 4 the body of the command APDU consists of a string of L bytes denoted by B1 to BL as illustrated by figure 5. Such a body carries 1 or 2 length fields; B1 is [part of] the first length field.

Command body

B1 B2 (L bytes)

Figure 5 - Not empty body

In the card capabilities (see 8.3.6), the card states that, within the command APDU, the Lc field and Le field

• either shall be short (one byte, default value)
• or may be extended (explicit statement)

Consequently, the cases 2, 3 and 4 are either short (one byte for each length field) or extended (B1 is valued to '00' and the value of each length is coded on 2 other bytes).

Table 5 shows the decoding of the command APDUs according to the four cases defined in table 4 and figure 4 and according to the possible extension of Lc and Le.

Table 5 - Decoding of the command APDUs

Conditions	Case
L=0	1

Decoding conventions for Le 
If the value of Le is coded in 1 (or 2) byte(s) where the bits are not all null, then the value of Le is equal to the value of the byte(s) which lies in the range from 1 to 255 (or 65535); the null value of all the bits means the maximum value of Le: 256 (or 65536).

The first 4 cases apply to all cards.

Case 1 - L=0 : the body is empty.

• No byte is used for Lc valued to 0
• No data byte is present.
• No byte is used for Le valued to 0.

Case 2S - L=1

• No byte is used for Lc valued to 0
• No data byte is present.
• B1 codes Le valued from 1 to 256

Case 3S - L=1 + (B1) and (B1) != 0

• B1 codes Lc (=0) valued from 1 to 255
• B2 to Bl are the Lc bytes of the data field
• No byte is used for Le valued to 0.

Case 4S - L=2 + (B1) and (B1) != 0

• B1 codes Lc (!=0) valued from 1 to 255
• B2 to Bl-1 are the Lc bytes of the data field
• Bl codes Le from 1 to 256

For cards indicating the extension of Lc and Le (see 8.3.8 card capabilities), the next 3 cases also apply.

Case 2E - L=3 and (B1)=0

• No byte is used for Lc valued to 0
• No data bytes is present
• The Le field consists of the 3 bytes where B2 and B3 code Le valued from 1 to 65536

Case 3E - L=3 + (B2||B3). (B1)=0 and (B2||B3)=0

• The Lc field consists of the first 3 bytes where B2 and B3 code Lc (!=0) valued from 1 to 65536
• B4 and B2 are the Lc bytes of the data field
• No byte is used for Le valued to 0

Case 4E - L= 5 + (B2||B3),(B1)=0 and (B2||B3)=0

• The Lc field consists of the first 3 bytes where B2 and B3 code Lc (!=0) valued from 1 to 65535
• B4 to Bl-2 are the Lc bytes of the data field
• The Le field consists of the last 2 bytes Bl-1 and Bl which code Le valued from 1 to 65536

For each transmission protocol defined in part 3 of ISO/IEC 7816 an annex attached to this part (one per protocol) specifies the transport of the APDUs of a command-response pair for each of the previous 4 cases.

5.3.3 Response APDU

Illustrated by figure 6 (see also table 7), the response APDU defined in this part of ISO/IEC 7816 consists of

• a conditional body of variable length
• a mandatory trailer of 2 bytes (SW1 SW2)

Body	Trailer
[Data field]	SW1 SW2

The number of bytes present in the data field of the response APDU is denoted by Lr.

The trailer codes the status of the receiving entity after processing the command-response pair.

NOTE - If the command is aborted, then the response APDU is a trailer coding an error condition on 2 status bytes.

5.4 Coding conventions for command headers, data fields and response trailers

5.4.1 Class byte 
5.4.2 Instruction byte

Table 6 shows the contents of the command APDU.

Table 6 - command APDU contents

Code	Name	Length	Description
CLA	Class	1	Class of instruction
INS	Instruction	1	Instruction code
P1	Parameter 1	1	Instruction parameter 1
P2	Parameter 2	1	Instruction parameter 2
Lc field	Length	variable 1 or 3	Number of bytes present in the data field of the command
Data field	Data	variable=Lc	String of bytes sent in the data field of the command
Le field	Length	variable 1 or 3	Maximum number of bytes expected in the data field of the response to the command

Table 7 shows the contents of the response APDU.

Table 7 - response APDU contents

Code	Name	Length	Description
Data field	Data	variable=Lr	String of bytes received in the data field of the response
SW1	Status byte 1	1	Command processing status
SW2	Status byte 2	1	Command processing qualifier

The subsequent clauses specify coding conventions for the class byte, the instruction byte, the parameter bytes, the data field bytes and the status byte. Unless otherwise specified, in those bytes, RFU bits are coded zero and RFU bytes are coded '00'.

5.4.1 Class byte

According to table 8 used in conjunction with table 9, the class byte CLA of a command is used to indicate

• to what extent the command and the response comply with this part of ISO/IEC 7816
• and when applicable (see table 9), the format of secure messaging and the logical channel number.

Table 8 - Coding and meaning of CLA

Value	Meaning
'0X'	Structure and coding of command and response according to this part of ISO/IEC 7816 (for coding of 'X' see table 9)
10 to 7F	RFU
8X, 9X	Structure of command and response according to this part of ISO/IEC 7816. Except for 'X' (for coding, see table 9), the coding and meaning of command and response are proprietary
AX	Unless otherwise specified by the application context, structure and coding of command and response according to this part of ISO/IEC 7816 (for coding of 'X', see table 9)
B0 to CF	Structure of command and response according to this part of ISO/IEC 7816
D0 to FE	Proprietary structure and coding of command and response
FF	Reserved for PTS

Table 9 - Coding and meaning of nibble 'X' when CLA='0X','8X','9X' or 'AX'

b4 b3 b2 b1	Meaning
x x -- --	Secure messaging (SM) format
0 x -- --	No SM or SM not according to 1.6
0 0 -- --	No SM or no SM indication
0 1 -- --	Proprietary SM format
1 x -- --	Secure messaging according to 1.6
1 0 -- --	Command header not authenticated
1 1 -- --	Command header authenticated (see 1.6.3.1 for command header usage)
-- -- x x	Logical channel number (according to 1.5) (b2 b1 = 00 when logical channels are not used or when logical channel #0 is selected

5.4.2 Instruction byte

The instruction byte INS of a command shall be coded to allow transmission with any of the protocols defined in part 3 of ISO/IEC 7816. Table 10 shows the INS codes that are consequently invalid.

Table 10 - Invalid INS codes

b8 b7 b6 b5 b4 b3 b2 b1	Meaning
x x x x x x x 1	Odd values
0 1 1 0 x x x x	'6X'
1 0 0 1 x x x x	'9X'

Table 11 shows the INS codes defined in this part of ISO/IEC 7816. When the value of CLA lies within the range from '00' to '7F', the other values of INS codes are to be assigned by ISO/IEC JTC 1 SC17.

Table 11 - INS codes defined in this part of ISO/IEC 7816

Value	Command name	Clause
'0E'	ERASE BINARY	6.4
'20'	VERIFY	6.12
'70'	MANAGE CHANNEL	6.16
'82'	EXTERNAL AUTHENTICATE	6.14
'84'	GET CHALLENGE	6.15
'88'	INTERNAL AUTHENTICATE	6.13
'A4'	SELECT FILE	6.11
'B0'	READ BINARY	6.1
'B2'	READ RECORD(S)	6.5
'C0'	GET RESPONSE	7.1
'C2'	ENVELOPE	7.2
'CA'	GET DATA	6.9
'D0'	WRITE BINARY	6.2
'D2'	WRITE RECORD	6.6
'D6'	UPDATE BINARY	6.3
'DA'	PUT DATA	6.10
'DC'	UPDATE DATA	6.8
'E2'	APPEND RECORD	6.7

5.4.3 Parameter bytes

The parameter bytes P1-P2 of a command may have any value. If a parameter byte provides no further qualification, then it shall be set to '00'.

5.4.4 Data field bytes

Each data field shall have one of the following three structures.

• Each TLV-coded data field shall consist of one or more TLV-coded data objects.
• Each non TLV-coded data field shall consist of one or more data elements, according to the specifications of the respective command.
• The structure of the proprietary-coded data fields is not specified in ISO/IEC 7816.

This part of ISO/IEC 7816 supports the following two types of TLV-coded data objects in the data fields :

• BER-TLV data objects
• SIMPLE-TLV data object

ISO/IEC 7816 uses neither '00' nor 'FF' as tag value.

Each BER-TLV data object shall consists of 2 or 3 consecutive fields (see ISO/IEC 8825 and annex D).

• The tag field T consists of one or more consecutive bytes. It encodes a class, a type and a number.
• The length field consists of one or more consecutive bytes. It encodes an integer L.
• If L is not null, then the value field V consists of L consecutive bytes. If L is null, then the data object is empty: there is no value field.

Each SIMPLE-TLV data object shall consist of 2 or 3 consecutive fields.

• The tag field T consists of a single byte encoding only a number from 1 to 254 (e.g. a record identifier). It codes no class and no construction-type.
• The length field consists of 1 or 3 consecutive bytes. If the leading byte of the length field is in the range from '00' to 'FE', then the length field consists of a single byte encoding an integer L valued from 0 to 254. If the leading byte is equal to 'FF', then the length field continues on the two subsequent bytes which encode an integer L with a value from 0 to 65535.
• If L in not null, then the value field V consists of consecutive bytes. If L is null, then the data object is empty: there is no value field.

The data fields of some commands (e.g. SELECT FILE ), the value fields of the SIMPLE-TLV data object and the value field of the some primitive BER-TLV data objects are intended for encoding one or more data elements.

The data fields of some other commands (e.g. record-oriented commands) and the value fields of the other primitive BER-TLV data objects are intended for encoding one or more SIMPLE-TLV data objects.

The data fields of some other commands (e.g. object-oriented commands) and the value fields of the constructed BER-TLV data objects are intended for encoding one or more BER-TLV data objects.

NOTE - Before between or after TLV-coded data objects, '00' or 'FF' bytes without any meaning may occur (e.g. due to erase or modified TLV-coded data objects).

5.4.5 Status bytes

The status bytes SW1-SW2 of a response denote the processing state in the card. Figure 7 shows the structural scheme of the values defined in this part of ISO/IEC 7816.

F I G U R E 7

Figure 7 - Structural scheme of status bytes

NOTE - When SW1='63' or '65', the state of the non-volatile memory is changed. When SW1='6X' except '63' and '65', the state of the non-volatile memory is unchanged.

Due to specifications in part 3 of ISO/IEC 7816, this part does not define the following values of SW1-SW2 :

• '60XX'
• '67XX', '6BXX', '6DXX', '6EXX', '6FXX'; in each case if 'XX'!='00'
• '9XXX', if 'XXX'!='000'

The following values of SW1-SW2 are defined whichever protocol is used (see examples in annex A).

• If a command is aborted with a response where SW1='6C', then SW2 indicates the value to be given to the short Le field (exact length of requested data) when re-issuing the same command before issuing any other command.
• If a command (which may be of case 2 or 4, see table 4 and figure 4) is processed with a response where SW1='61', then SW2 indicates the maximum value to be given to the short Le field (length of extra data still available) in a GET RESPONSE command issued before issuing any other command.

NOTE - A functionality similar to that offered by '61XX' may be offered at application level by '9FXX'. However, applications may use '9FXX' for other purposes.

Table 12 completed by tables 13 to 18 shows the general meanings of the values of SW1-SW2 defined in this part of ISO/IEC 7816. For each command, an appropriate clause provides more detailed meanings.

Tables 13 to 18 specify values of SW2 when SW1 is valued to '62', '63', '65', '68', '69' and '6A'. The values of SW2 not defined in tables 13 to 18 are RFU, except the values from 'F0' to 'FF' which are not defined in this part of ISO/IEC 7816.

Table 12 - Coding of SW1-SW2

SW1-SW2	Meaning
	Normal processing
'9000'	No further qualification
'61XX'	SW2 indicates the number of response bytes still available (see text below)
	Warning processings
'62XX'	State of non-volatile memory unchanged (further qualification in SW2, see table 13)
'63XX'	State of non-volatile memory changed (further qualification in SW2, see table 14)
	Execution errors
'64XX'	State of non-volatile memory unchanged (SW2='00', other values are RFU)
'65XX'	State of non-volatile memory changed (further qualification in SW2, see table 15)
'66XX'	Reserved for security-related issues (not defined in this part of ISO/IEC 7816)
	Checking errors
'6700'	Wrong length
'68XX'	Functions in CLA not supported (further qualification in SW2, see table 16)
'69XX'	Command not allowed (further qualification in SW2, see table 17)
'6AXX'	Wrong parameter(s) P1-P2 (further qualification in SW2, see table 18)
'6B00'	Wrong parameter(s) P1-P2
'6CXX'	Wrong length Le: SW2 indicates the exact length (see text below)
'6D00'	Instruction code not supported or invalid
'6E00'	Class not supported
'6F00'	No precise diagnosis

Table 13 - Coding of SW2 when SW1='62'

SW2	Meaning
'00'	No information given
'81'	Part of returned data may be corrupted
'82'	End of file/record reached before reading Le bytes
'83'	Selected file invalidated
'84'	FCI not formatted according to 1.1.5

Table 14 - Coding of SW2 when SW1='63'

SW2	Meaning
'00'	No information given
'81'	File filled up by the last write
'CX'	Counter provided by 'X' (valued from 0 to 15) (exact meaning depending on the command)

Table 15 - Coding of SW2 when SW1='65'

SW2	Meaning
'00'	No information given
'81'	Memory failure

Table 16 - Coding of SW2 when SW1='68'

SW2	Meaning
'00'	No information given
'81'	Logical channel not supported
'82'	Secure messaging not supported

Table 17 - Coding of SW2 when SW1='69'

SW2	Meaning
'00'	No information given
'81'	Command incompatible with file structure
'82'	Security status not satisfied
'83'	Authentication method blocked
'84'	Referenced data invalidated
'85'	Conditions of use not satisfied
'86'	Command not allowed (no current EF)
'87'	Expected SM data objects missing
'88'	SM data objects incorrect

Table 18 - Coding of SW2 when SW1='6A'

SW2	Meaning
'00'	No information given
'80'	Incorrect parameters in the data field
'81'	Function not supported
'82'	File not found
'83'	Record not found
'84'	Not enough memory space in the file
'85'	Lc inconsistent with TLV structure
'86'	Incorrect parameters P1-P2
'87'	Lc inconsistent with P1-P2
'88'	Referenced data not found

5.5 Logical channels

5.5.1 General concept

A logical channel, as seen at the interface, works as a logical link to a DF.

There shall be independence of activity on one logical channel from activity on another one. That is, command interdependencies on one logical channel shall be independent of command interdependencies on another logical channel. However, logical channels may share application-dependent security status and therefore may have security-related command interdependencies across logical channels (e.g. password verification).

Commands referring to a certain logical channel carry the respective logical channel number in the CLA byte (see tables 8 and 9 ). Logical channels are numbered from 0 to 3. If a card supports the logical channel mechanism, then the maximum number of available logical channels is indicated in the card capabilities (see 8.3.6).

Command-response pairs work as currently described. This part of ISO/IEC 7816 supports only command-response pairs which shall be completed before initiating a subsequent command-response pair. There shall be no interleaving of commands and their responses across logical channels; between the receipt of a command and the sending of the response to that command only channel is opened it remains open until explicity closed by a MANAGE CHANNEL command .

NOTES

1. More than one logical channel may be opened to the same DF, if not excluded (see file accessibility in 1.1.5)
2. More than one logical channel may select the same EF if not excluded (see file accessibility in 1.1.5)
3. A SELECT FILE command on any logical channel will open a current DF and possibly a current EF. Therefore, there is one current DF and possibly one current EF per logical channel as a result of the behavior of the SELECT FILE command and file accessing commands using a short EF identifier.

5.5.2 Basic logical channel

The basic logical channel is permanently available. When numbered, its number is 0. When the class byte is coded according to table 8 and 9 , the bits b1 and b2 code the logical channel number.

5.5.3 Opening a logical channel

A logical channel is opened by successful completion of

• either a SELECT FILE command referencing a DF by assigning a logical channel number other than the class byte
• or the open function of the MANAGE CHANNEL command either assigning a logical channel number other than 0 in the command APDU or requesting a logical channel number to be assigned by the card and returned in the response.

5.5.4 Closing a logical channel

The close function of the MANAGE CHANNEL command may be used to explicitly close a logical channel using the logical channel number. After closing the logical channel number will be available for re-use. The basic logical channel shall not be closed.

5.6 Secure messaging

5.6.1 SM format concept 
5.6.2 Plain value data object 
5.6.3 Data object for authentication 
5.6.3.1 Cryptographic checksum data object 
5.6.3.2 Digital signature data object 
5.6.4 Data objects for confidentiality 
5.6.5 Auxiliary security data objects 
5.6.5.1 Control references 
5.6.5.2 Response descriptor 
5.6.6 SM status conditions

The goal of secure messaging (SM) is to protect [part of] the messages to and from a card by ensuring two basic security functions: data authentication and data confidentiality.

Secure messaging is achieved by applying one or more security mechanisms. Each security mechanism involves an algorithm, a key, an argument and often, initial data.

• The transmission and reception of data fields may be interleaved with the execution of security mechanisms. This specification does not preclude the determination by sequential analysis of which mechanisms and which security items shall be used for processing the remaining part of the data field.
• Two or more security mechanisms may use the same algorithm with different modes of operation (see ISO/IEC 7816). The present specifications of the padding rules do not preclude such a feature.

  This clause defines 3 types of SM-related data objects :

  • plain value data objects, intended for carrying plain data,
  • security mechanism data objects, intended for carrying computational results of security mechanisms.
  • auxiliary security data objects, intended for carrying control references and response descriptors.

5.6.1 SM format concept

In each message involving security mechanisms based on cryptography, the data field shall comply with the basic encoding rules of ASN.1 (see ISO/IEC 8825 and annex D), unless otherwise indicated by the class byte (see 1.4.1).

In the data field, the present SM format may be selected

• implicitly, i.e. known before issuing the command
• explicitly, i.e. fixed by the class byte (see table 9)

The SM format defined in this part of ISO/IEC 7816 is BER-TLV coded.

• The context-specific class of tags (range from '80' to 'BF') is reserved for SM.
• Data objects of the other classes may be present (e.g. data objects of the application-specifc class)
• Some SM-related data objects are recursive: their plain value field is still BER-TLV coded and there, the context-specific class is still reserved for SM.

In the context-specific class, the bit 1 of the tag fixes whether the SM-related data object shall (b1=1) or not (b1=0) be integrated in the computation of a data object for authentication. If present, the data objects of the other classes shall be integrated in such a computation.

5.6.2 Plain value data objects

Encapsulation is mandatory for data not coded in BER-TLV and for BER-TLV, including SM-related data objects. Encapsulation is optional for BER-TLV, not including SM-related data objects. Table 19 shows plain data objects for encapsulation.

Table 19 - Plain value data objects

Tag	Value
'B0','B1'	BER-TLV, including SM-related data objects
'B2','B3'	BER-TLV, but not SM-related data objects
'80','81'	not BER-TLV-coded data
'99'	SM status information (e.g. SW1-SW2)

5.6.3 Data objects for authentication

5.6.3.1 Cryptographic checksum data object

The computation of cryptographic checksums (see ISO/IEC 9797) involves an initial check block, secret key and a block cipher algorithm that need not be reversible. The algorithm under control of the related key basically transforms a current input block of k bytes (typically 8 or 16) into a current output block of the same length.

The computation of a cryptographic checksum is performed in the following consecutive stages :

• Initial stage - The initial stage sets the initial check block which shall be one of the following blocks :
  • the null block, i.e. k bytes valued to '00'
  • the chaining block, i.e. a result from former computations, namely for a command, the final check block of the previous command and for a response the final check block of the previous response.
  • the initial value block provided e.g. by the outside world
  • the auxiliary block resulting from transforming auxiliary data under the related key. If the auxiliary data is less than k bytes, then it is headed by bits set to 0, up to the block length.
• Sequential stage - When table 9 is applicable (CLA='0X','8X','9X' or 'AX'), if bits b4 and b3 of the class byte are set to 1, then the first data block consists of the header of the command APDU (CLA INS P1 P2) followed by one byte valued to '80' and k-5 bytes valued to '00'.

  The cryptographic checksum shall integrate any SM-related data object having a tag where b1=1 and any data object with a tag outside the range from '80' to 'BF'. Those data objects shall integrate data block by data block in the current check block. The splitting into data blocks shall be performed in the following way.

  • The blocking shall be continuous at the border between adjacent data objects to be integrated
  • The padding shall apply at the end of each data object to be integrated followed either by a data object not to be integrated or by no further data object.

  The padding consists of one mandatory byte valued to '80' followed, if needed, by 0 to k-1 bytes set to '00', until the respective data block is filled up to k bytes. Padding for authentication has no influence on transmission as the padding bytes shall not be transmitted.

  The mode of operation is "cipher block chaining" (see ISO/IEC 10116). The first input is the exclusive-or of the initial check block with the first data block. The first output results from the first data block. The first output results from the first input. The current input is the exclusive-or of the previous output with the current data block. The current output results from the current input. The final check block is the last output.

• Final stage - The final stage extracts a cryptographic checksum (first m bytes, at least 4) from the final check block.

Table 20 shows the cryptographic checksum data object.

Table 20 - Cryptographic checksum data object

Tag	Value
'8E'	Cryptographic checksum (at least 4 bytes)

5.5.3.2 Digital signature data object

The digital signature computation is typically based upon asymmetric cryptographic techniques. There are two types of digital signatures :

• digital signature with appendix
• digital signature giving message recovery

The computation of a digital signature with appendix implies the use of a hash function (see ISO/IEC 10118). The data input either consists of the value of the digital signature input data object (see table 21 ), or is determined by the mechanism define in 1.6.3.1.

The computation of a digital signature related data objects.

Table 21 - Digital signature related data objects

Value

Tag
'9A','BA'	Digital signature input data
'9E'	Digital signature

5.6.4 Data objects for confidentiality

Data objects for confidentiality are intended for carrying a cryptogram which plain value consists of one of the following 3 cases :

• BER-TLV, including SM-related data objects
• BER-TLV, not including SM-related data bojects
• not BER-TLV coded data

Padding has to be indicated when the plain value consists of not BER-TLV coded data. When padding is applied but not indicated the rules defined in 1.6.3.1 shall apply.

Table 22 - Data objects for confidentiality

Tag	Value
'82','83'	BER-TLV, including SM-related data objects
'84','85'	BER-TLV, but not SM-related data objects
'86','87'	Padding indicator byte (see table 23) followed by cryptogram (plain not coded in BER-TLV)

Every data object for confidentiality may use any cryptographic algorithm and any mode of operation owning to an appropriate algorithm reference (see 1.6.5.1). In the absence of an algorithm reference and when no mechanism is implicitly selected for confidentiality a default mechanism shall apply.

For the computation of a cryptogram which is preceded by the padding indicator, the default mechanism is block cipher in "electronic code book" mode (see ISO/IEC 10116). The use of a block cipher may involve padding. Padding for confidentiality has an influence on transmission, the cryptogram (one or more blocks is longer than the plain text).

Table 23 shows the padding indicator byte

Table 23 - Padding indicator byte

Value	Meaning
'00'	No further indication
'01'	Padding as defined in 1.6.3.1
'02'	No padding
'80' to '8E'	Proprietary
	Other values are RFU

For the computation of a cryptogram not preceded by a padding indicator byte, the default mechanism is a stream cipher with exclusive-or of the string of data bytes to be concealed with a concealing string of the same length. Concealment thus requires no padding and the data objects concealed in the value field are recovered by the same operation.

5.6.5 Auxiliary security data objects

An algorithm, a key and, possibly initial data may be selected for each security mechanism

• implicitly, i.e. known before issuing the command
• explicitly, by control references nested in a control reference template

Each command message may carry a response descriptor template fixing the data objects required in response. Inside the response descriptor, the security mechanisms are not yet applied: the receiving entity shall apply them for constructing the response.

5.6.5.1 Control references

Table 24 shows the control reference templates.

Table 24 - Control reference templates

Tag	Meaning
'B4','B5'	Template valid for cryptographic checksum
'B6','B7'	Template valid for digital signature
'B8','B9'	Template valid for confidentiality

The last possible position of a control reference template is just before the first data object to which the referred mechanism applies. For example, the last possible position of a template for cryptographic checksum is just before the first data object integrated in the computation.

Each control reference remains valid until a new control reference is provided for the same mechanism. For example, a command may fix control references for the next command.

Each control reference template is intended for carrying control reference data objects (see table 25 ): an algorithm reference, a file reference, a key reference, an initial data reference and only in a control reference template for confidentiality a cryptogram contents reference.

The algorithm reference fixes an algorithm and its mode of operation (see ISO/IEC 9979 and 10116). Structure and coding of the algorithm reference are not defined in this part of ISO/IEC 7816.

The file reference denotes the file where the key reference is valid. If no file reference is present, then the key reference is valid in the current DF.

The key reference identifies the key to be used.

The initial data reference, when applied to cryptographic checksums, fixes the initial check block. If no initial data reference is present and no initial check block is implicitly selected, then the null block shall be used. Moreover, before transmitting the first data object for confidentiality using a stream cipher, a template for confidentiality shall provide auxiliary data for initializing the computation of the string of concealing bytes.

The cryptogram contents reference specifies the content of the cryptogram (e.g. secret key, initial password, control words). The first byte of the value field is named the type cryptogram descriptor byte and is mandatory. The range '00' to '7F' is RFU. The range '80' to 'FF' is proprietary.

Table 25 - Control reference data objects

Tag	Value
'80'	Alogorithm reference
	File reference
'81'	- file identifier or path
'82'	- DF name
	Key reference
'83'	- for direct use
'84'	- for computing a session key
	Initial data reference
'85'	- L=0, null block
'86'	- L=0, chaining block
'87'	- L=0, previous initial value block plus one L=k, initial value block
	Auxiliary data
'88'	- L=0, previous exchanged challenge plus one L!=0, no further indication
'89'-'8D'	- L=0, index of a proprietary data element, L!=0, value of a proprietary data element
'8E'	Cryptogram contents reference

5.6.5.2 Response descriptor

The response descriptor template, if present in the data field of the command APDU, shall fix the structure of the corresponding response. Empty data objects shall list all data needed for producing the response.

The security items (algorithms, key and initial data) used for processing the data field of a command message may be different from those used for producing the data field of the subsequent response messsage.

The following rules shall apply

• The card shall fill each empty primitive data object
• Each control reference template present in the response descriptor shall be present in the response at the same place with the same control references for algorithm, file and key. If the response descriptor provides auxiliary data, then the respective data object shall be empty in the response. If an empty reference data object for auxiliary data is present in the response descriptor, then it shall be full in the response.
• By the relevant security mechanisms, with the selected security items, the card shall produce all the requested security mechanism data objects.

Table 26 shows the response descriptor template.

Table 26 - Response descriptor template

Tag	Value
'BA','BB'	Response descriptor

5.6.6 SM status conditions

In any command using secure messaging the following specific error conditions may occur: 

SW1='69' with SW2=

• '87': Expected SM data objects missing
• '88': SM data objects incorrect