ISO/IEC 19772:2020
(Main)Information security — Authenticated encryption
Information security — Authenticated encryption
This document specifies five methods for authenticated encryption, i.e. defined ways of processing a data string with the following security objectives: — data confidentiality, i.e. protection against unauthorized disclosure of data; — data integrity, i.e. protection that enables the recipient of data to verify that it has not been modified; — data origin authentication, i.e. protection that enables the recipient of data to verify the identity of the data originator. All five methods specified in this document are based on a block cipher algorithm, and require the originator and the recipient of the protected data to share a secret key for this block cipher. Key management is outside the scope of this document. Key management techniques are defined in ISO/IEC 11770 (all parts). Four of the mechanisms in this document, namely mechanisms 3, 4, 5 (AAD variant only) and 6, allow data to be authenticated which is not encrypted. That is, these mechanisms allow a data string that is to be protected to be divided into two parts, D, the data string that is to be encrypted and integrity-protected, and A (the additional authenticated data) that is integrity-protected but not encrypted. In all cases, the string A can be empty. NOTE Examples of types of data that can need to be sent in unencrypted form, but whose integrity is to be protected, include addresses, port numbers, sequence numbers, protocol version numbers and other network protocol fields that indicate how the plaintext is to be handled, forwarded or processed.
Sécurité de l'information — Chiffrement authentifié
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Standards Content (Sample)
INTERNATIONAL ISO/IEC
STANDARD 19772
Second edition
2020-11
Information security — Authenticated
encryption
Sécurité de l'information — Chiffrement authentifié
Reference number
©
ISO/IEC 2020
© ISO/IEC 2020
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ii © ISO/IEC 2020 – All rights reserved
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 3
5 Requirements . 4
6 Authenticated encryption mechanism 2 (key wrap) . 5
6.1 General . 5
6.2 Specific notation . 5
6.3 Specific requirements . 5
6.4 Encryption procedure . 5
6.5 Decryption procedure . 6
7 Authenticated encryption mechanism 3 (CCM) . 6
7.1 General . 6
7.2 Specific notation . 7
7.3 Specific requirements . 7
7.4 Encryption procedure . 7
7.5 Decryption procedure . 9
8 Authenticated encryption mechanism 4 (EAX) .10
8.1 General .10
8.2 Specific notation .10
8.3 Specific requirements .10
8.4 Definition of function M .10
8.5 Encryption procedure .11
8.6 Decryption procedure .11
9 Authenticated encryption mechanism 5 (encrypt-then-MAC) .12
9.1 General .12
9.2 Specific notation .12
9.3 Specific requirements .12
9.4 Encryption procedure .13
9.5 Decryption procedure .13
10 Authenticated encryption mechanism 6 (GCM) .14
10.1 General .14
10.2 Specific notation .14
10.3 Specific requirements .15
10.4 Definition of multiplication operation • .15
10.5 Definition of function G .15
10.6 Encryption procedure .16
10.7 Decryption procedure .16
Annex A (informative) Guidance on the use of the mechanisms .18
Annex B (informative) Numerical examples .21
Annex C (normative) Object identifiers .25
Bibliography .26
© ISO/IEC 2020 – All rights reserved iii
Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that
are members of ISO or IEC participate in the development of International Standards through
technical committees established by the respective organization to deal with particular fields of
technical activity. ISO and IEC technical committees collaborate in fields of mutual interest. Other
international organizations, governmental and non-governmental, in liaison with ISO and IEC, also
take part in the work.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for
the different types of document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject
of patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent
rights. Details of any patent rights identified during the development of the document will be in the
Introduction and/or on the ISO list of patent declarations received (see www .iso .org/ patents) or the IEC
list of patent declarations received (see http:// patents .iec .ch).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/IEC JTC 1, Information Technology,
Subcommittee SC 27, Information security, cybersecurity and privacy protection.
This second edition cancels and replaces the first edition (ISO/IEC 19772:2009) which has been
technically revised. It also incorporates the Technical Corrigendum ISO/IEC 19772:2009/Cor 1:2014.
The main changes compared to the previous edition are as follows:
— old Clause 6 has been removed following the deprecation of mechanism 1 (OCB 2.0);
— optional additional authenticated data has been included in mechanism 5.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO/IEC 2020 – All rights reserved
Introduction
When data is sent from one place to another, it is often necessary to protect it in some way while it is in
transit, e.g. against eavesdropping or unauthorized modification. Similarly, when data is stored in an
environment to which unauthorized parties can have access, it can be necessary to protect it.
If the confidentiality of the data needs to be protected, e.g. against eavesdropping, then one solution
is to use encryption, as specified in ISO/IEC 18033 (all parts) and ISO/IEC 10116. Alternatively,
if it is necessary to protect the data against modification, i.e. integrity protection, then message
authentication codes (MACs) as specified in ISO/IEC 9797 (all parts), or digital signatures as specified in
ISO/IEC 9796 (all parts) and ISO/IEC 14888 (all parts), can be used. If both confidentiality and integrity
protection are required, then one possibility is to use both encryption and a MAC or signature. While
these operations can be combined in many ways, not all combinations of such mechanisms provide
the same security guarantees. As a result, it is desirable to define in detail exactly how integrity and
confidentiality mechanisms should be combined to provide the optimum level of security. Moreover, in
some cases, significant efficiency gains can be obtained by defining a single method of processing the
data with the objective of providing both confidentiality and integrity protection.
In this document, authenticated encryption mechanisms are defined. These are methods for processing
data to provide both integrity and confidentiality protection. They typically involve either a specified
combination of a MAC computation and data encryption, or the use of an encryption algorithm in a
special way such that both integrity and confidentiality protection are provided.
The methods specified in this document have been designed to maximize the level of security and
provide efficient processing of data. Some of the techniques defined here have mathematical "proofs of
security", i.e. rigorous arguments supporting their soundness.
© ISO/IEC 2020 – All rights reserved v
INTERNATIONAL STANDARD ISO/IEC 19772:2020(E)
Information security — Authenticated encryption
1 Scope
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