ISO 16609:2012
(Main)Financial services — Requirements for message authentication using symmetric techniques
Financial services — Requirements for message authentication using symmetric techniques
Services financiers — Exigences pour l'authentification des messages utilisant des techniques symétriques
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INTERNATIONAL ISO
STANDARD 16609
Second edition
2012-03-15
Financial services — Requirements
for message authentication using
symmetric techniques
Services financiers — Exigences pour l’authentification des messages
utilisant des techniques symétriques
Reference number
ISO 16609:2012(E)
©
ISO 2012
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ISO 16609:2012(E)
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ISO 16609:2012(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International
Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 16609 was prepared by Technical Committee ISO/TC 68, Financial services, Subcommittee SC 2,
Financial services, security.
This second edition cancels and replaces the first edition (ISO 16609:2004), which has been technically revised.
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ISO 16609:2012(E)
Introduction
A MAC (message authentication code) is a data field used to verify the authenticity of a message, generated by
the sender of the message and transmitted together with it. The MAC enables an intended recipient to detect
whether the message has been altered. While non-keyed message integrity methods, e.g. checksums, only
protect against accidental alteration of the message, MACs additionally protect against deliberate alteration
since the adversary would not have access to the key used to generate the MAC.
This International Standard has been prepared so that institutions involved in financial services activities wishing
to implement message authentication can do so in a manner that is secure and facilitates interoperability
between separate implementations.
This International Standard identifies ciphers, hash functions and algorithms from ISO 9797 (all parts) that are
specifically approved for secure banking purposes.
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INTERNATIONAL STANDARD ISO 16609:2012(E)
Financial services — Requirements for message authentication
using symmetric techniques
1 Scope
This International Standard specifies procedures, independent of the transmission process, for protecting the
integrity of transmitted banking messages and for verifying that a message has originated from an authorized
source. A list of block ciphers approved for the calculation of a message authentication code (MAC) is also
provided. The authentication methods it defines are applicable to messages formatted and transmitted both as
coded character sets and as binary data.
This International Standard is designed for use with symmetric algorithms where both sender and receiver use
the same key. It does not specify methods for establishing the shared key, nor does it provide for encipherment
for the protection of messages against unauthorized disclosure. Its application will not protect the user against
internal fraud perpetrated by the sender or the receiver, nor against forgery of a MAC by the receiver.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced document
(including any amendments) applies.
ISO/IEC 9797-1:2011, Information technology — Security techniques — Message Authentication Codes
(MACs) — Part 1: Mechanisms using a block cipher
ISO/IEC 9797-2, Information technology — Security techniques — Message Authentication Codes (MACs) —
Part 2: Mechanisms using a hash-function
ISO 11568-1, Banking — Key management (retail) — Part 1: Principles
ISO 11568-2, Financial services — Key management (retail) — Part 2: Symmetric ciphers, their key management
and life cycle
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
algorithm
specified mathematical process for computation or set of rules which, if followed, will give a prescribed result
3.2
authentication
process used between a sender and a receiver to ensure data integrity and provide data origin authentication
3.3
authentication algorithm
algorithm used, together with an authentication key and one or more authentication elements, for authentication
3.4
authentication element
message element that is to be protected by authentication
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ISO 16609:2012(E)
3.5
authentication key
cryptographic key used for authentication
3.6
beneficiary
ultimate party to be credited or paid as a result of a transfer
NOTE There can be more than one beneficiary.
3.7
block cipher
algorithm for computing a function which maps a fixed-length string of bits and a secret key to another string
of bits with the same fixed length
3.8
checksum
fixed-length string of bits calculated from a message of arbitrary length, such that it is unlikely that a change of one
or more bits in the message will produce the same string of bits, thereby aiding detection of accidental modification
3.9
cryptoperiod
defined period of time during which a specific cryptographic key is authorized for use or during which the
cryptographic keys in a given system may remain in effect
3.10
data integrity
property pertaining to data that has not been altered or destroyed in an unauthorized manner
3.11
DMC
date MAC computed
date on which the sender computed the MAC (message authentication code)
NOTE The DMC can be used to synchronize the authentication process through selection of the proper key.
3.12
data origin authentication
corroboration that the source of data received is as claimed
3.13
encipherment
(reversible) transformation of data by a cryptographic algorithm with a cryptographic key in order to produce
ciphertext, i.e. to hide the information content of the data
3.14
identifier for authentication key
IDA
field that identifies the key to be used in authenticating the message
3.15
MAC
message authentication code
fixed-length string of bits used to verify the authenticity of a message, generated by the sender of the message,
transmitted together with the message, and verified by the receiver of the message
3.16
MAC algorithm
keyed cryptographic algorithm that produces a fixed-length string of bits (the MAC) from a message of arbitrary
length, such that it is not feasible to compute the MAC without knowledge of the key
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ISO 16609:2012(E)
3.17
message element
contiguous group of bytes designated for a specific purpose
3.18
MID
message identifier
systems trace audit number (deprecated)
field used uniquely to identify a financial message or transaction (e.g. sending bank’s transaction reference)
within a given context (e.g. DMC)
NOTE In ISO 8583, the MID was referred to as the systems trace audit number (STAN), which it supersedes.
3.19
message text
information conveyed or transmitted between sender and receiver, excluding header and trailer information
used for transmission purposes
3.20
receiver
party intended to receive the message
3.21
sender
party responsible for, and authorized to, send a message
3.22
value date
date on which funds are to be at the disposal of the beneficiary
4 Protection
4.1 Protection of authentication keys
Authentication keys are secret cryptographic keys that have been previously established by the sender and
receiver and which are used by the authentication algorithm. Keys shall be managed in accordance with
ISO 11568-1 and ISO 11568-2.
4.2 Authentication elements
The MAC calculation shall include those message elements, as agreed between sender and receiver, which
require protection against fraudulent alteration.
Subject to bilateral agreement, the MAC calculation may also cover data elements not transmitted in the
message (e.g. padding bits or data computable by both parties from information already shared).
The choice of data to be included in the MAC will depend on the specific application. When the following
elements appear in a message, they should be included in the calculation of the MAC:
a) transaction amount;
b) currency;
c) identifier for authentication key (IDA);
d) identification of payer and beneficiary and/or, if appropriate, their payment agent’s value date;
e) message identifier;
f) date and time;
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ISO 16609:2012(E)
g) indication as to the disposition of the transaction.
NOTE Integrity protection applies only to the selected authentication elements. Other parts of the message can be
subject to undetected alterations. It is important that users ensure the integrity of data presentation.
4.3 Detection of duplication, loss or sequence errors
A mechanism should be implemented to detect duplication or loss, or messages arriving out of sequence.
Without recourse to further message exchanges, the recipient may only detect the replay of a previous
transaction if able to identify transactions uniquely, and should then check that such unique identifying
information has not already occurred. To detect sequence errors, messages should be identifiable as being
in a sequence. Furthermore, in order to detect loss, transactions should be identifiable as being in a defined
sequence, predictable by the recipient. These conditions are achieved by involving in the MAC computation
some elements (i.e. message elements or key elements) that are unique to the transaction and that relate it
uniquely to the previous transaction. This may be achieved in one of the following ways.
a) Include in the MAC calculation a unique transaction reference that does not repeat within the lifetime of
the system. To detect loss, the reference would need to change in a defined sequence that is known by
the recipient who calculates this value and compares it to the received value.
EXAMPLE The reference will include sender ID, recipient ID, key ID and transaction number, where the transaction
number increases by one for each transaction.
b) Include in the MAC calculation a MID, i.e. a value that does not repeat before either
— the change of date, i.e. DMC (usable if the date is included in MAC elements), or
— the expiration of the cryptoperiod of the key used for authentication.
The MID may consist of a unique sending bank’s transaction reference number in a fixed format message
as a message identifier. A method of protection is described in Annex A. The MID may either contain the
DMC or be a separate field. To simplify detection of loss, the MID could increase in a defined sequence.
c) Use a unique key per transaction where the key of one transaction is derived from that of the previous
transaction (see ISO 11568-2).
d) Combine the above techniques.
5 Procedures for message authentication
5.1 MAC generation
The sender of a message shall generate a MAC by processing in an agreed order (e.g. the sequence in
which they appear in the message) those authentication elements of the transmitted message that are to be
protected by an approved authentication mechanism (see 4.2). The mechanism shall be activated by means of
an authentication key, which is a secret between the two correspondents. This process creates the MAC, which
shall then be included with the original message text.
5.2 MAC placement
The MAC shall be either
a) placed in the message, in an additional field specified for the transport of the MAC, or
b) appended to the data portion of the message, if there is no specified MAC field.
Where the field allocated has a length, for transport, greater than the MAC length, the MAC shall be positioned
by left-justifying it within the field.
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ISO 16609:2012(E)
5.3 MAC verification
On receipt of the message, the receiver shall compute a reference MAC using the authentication elements,
an identical authentication key and an identical algorithm. Authenticity of the content of the authentication
elements and the message source shall be considered to have been confirmed when the receiver’s computed
reference MAC agrees with that received with the message text.
A received MAC is not included in the algorithm computation.
The process of generating the MAC is sensitive to the sequence in which the authentication elements are
processed (i.e. a change in the sequence of authentication elements after the MAC is generated will result in
a failure to authenticate).
5.4 Approved authentication mechanisms based on ISO/IEC 9797
5.4.1 General
The MAC algorithm shall be one of those specified in ISO/IEC 9797-1 or ISO/IEC 9797-2.
5.4.2 Approved authentication mechanisms based on ISO/IEC 9797
ISO/IEC 9797-1 s
...
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