ISO/IEC 18033-1:2021
(Main)Information security — Encryption algorithms — Part 1: General
Information security — Encryption algorithms — Part 1: General
This document is general in nature and provides definitions that apply in subsequent parts of the ISO/IEC 18033 series. It introduces the nature of encryption and describes certain general aspects of its use and properties.
Sécurité de l'information — Algorithmes de chiffrement — Partie 1: Généralités
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INTERNATIONAL ISO/IEC
STANDARD 18033-1
Third edition
2021-09
Information security — Encryption
algorithms —
Part 1:
General
Sécurité de l'information — Algorithmes de chiffrement —
Partie 1: Généralités
Reference number
©
ISO/IEC 2021
© ISO/IEC 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO/IEC 2021 – 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 . 5
5 Nature of encryption . 5
5.1 Purpose of encryption . 5
5.2 Symmetric and asymmetric encryption systems . 6
5.3 Key management . 6
6 Use and properties of encryption . 6
6.1 General . 6
6.2 Asymmetric encryption systems . 7
6.3 Block ciphers . 7
6.3.1 General. 7
6.3.2 Modes of operation . 7
6.3.3 Message authentication codes (MACs) . 7
6.4 Stream ciphers . 8
6.5 Identity-based encryption systems . 8
6.6 Homomorphic encryption systems . 8
7 Object identifiers . 8
Annex A (informative) Criteria for submission of encryption systems for possible inclusion
in the ISO/IEC 18033 series . 9
Annex B (informative) Criteria for the deletion of encryption systems from
the ISO/IEC 18033 series .14
Annex C (informative) Attacks on encryption algorithms .15
Bibliography .18
© ISO/IEC 2021 – 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 or www .iec .ch/ members
_experts/ refdocs).
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 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. In the IEC, see www .iec .ch/ understanding -standards.
This document was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 27, Information security, cybersecurity and privacy protection.
This third edition cancels and replaces the second edition (ISO/IEC 18033-1:2015), which has been
technically revised. The main changes compared with the previous edition are as follows:
— Clause 3 has been refined;
— criteria for submission of encryption systems have been refined for possible inclusion in the
ISO/IEC 18033 series; and
— the use and security properties of encryption algorithms have been clarified.
A list of all parts in the ISO/IEC 18033 series can be found on the ISO website.
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 and www .iec .ch/ national
-committees.
iv © ISO/IEC 2021 – All rights reserved
Introduction
The ISO/IEC 18033 series specifies encryption systems for the purpose of data confidentiality. The
inclusion of encryption systems in this document is intended to promote their use as reflecting the
current state of the art in encryption systems.
The primary purpose of encryption systems is to protect the confidentiality of stored or transmitted
data. An encryption algorithm is applied to data (often called plaintext) to yield encrypted data (or
ciphertext). This process is known as encryption. The encryption algorithm should be designed so that
the ciphertext yields no information about the plaintext except, perhaps, its length. Associated with
every encryption algorithm is a corresponding decryption algorithm, which transforms ciphertext
back into its original plaintext.
Encryption systems work in association with a key. In a symmetric encryption system, the same key is
used in both the encryption and decryption algorithms. In an asymmetric encryption system, different
but related keys are used for encryption and decryption. ISO/IEC 18033-2 and ISO/IEC 18033-5 focus
on two different classes of asymmetric encryption systems, known as conventional asymmetric
encryption systems (or just asymmetric encryption systems), and identity-based encryption systems.
ISO/IEC 18033-3 and ISO/IEC 18033-4 focus on two different classes of symmetric encryption systems,
known as block ciphers and stream ciphers. ISO/IEC 18033-6 focuses on a specific class of encryption
systems called homomorphic.
© ISO/IEC 2021 – All rights reserved v
INTERNATIONAL STANDARD ISO/IEC 18033-1:2021(E)
Information security — Encryption algorithms —
Part 1:
General
1 Scope
This document is general in nature and provides definitions that apply in subsequent parts of the
ISO/IEC 18033 series.
It introduces the nature of encryption and describes certain general aspects of its use and properties.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 18033-2, Information technology — Security techniques — Encryption algorithms — Part 2:
Asymmetric ciphers
ISO/IEC 18033-3, Information technology — Security techniques — Encryption algorithms — Part 3: Block
ciphers
ISO/IEC 18033-4, Information technology — Security techniques — Encryption algorithms — Part 4:
Stream ciphers
ISO/IEC 18033-5, Information technology — Security techniques — Encryption algorithms — Part 5:
Identity-based ciphers
ISO/IEC 18033-6, IT Security techniques — Encryption algorithms — Part 6: Homomorphic encryption
ISO/IEC 18033-7, Information technology — Security techniques — Encryption algorithms — Part 7:
Tweakable block ciphers
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
asymmetric cryptographic technique
cryptographic technique that uses two related transformations, a public transformation [defined by
the public key (3.22)] and a private transformation [defined by the private key (3.21)]
Note 1 to entry: The two transformations have the property that, given the public transformation, it is
computationally infeasible to derive the private transformation. Computational feasibility depends on the
specific security requirements and environment.
[SOURCE: ISO/IEC 11770-1:2010, 2.1, modified — The last sentence in note 1 to entry has been added.]
© ISO/IEC 2021 – All rights reserved 1
3.2
asymmetric encryption system
asymmetric cipher
asymmetric encipherment system
system based on asymmetric cryptographic techniques (3.1) whose public transformation is used for
encryption (3.11) and whose private transformation is used for decryption (3.9)
Note 1 to entry: A method for key (3.17) pair generation is assumed.
[SOURCE: ISO/IEC 9798-1:2010, 3.2, modified — The admitted terms "asymmetric cipher" and
"asymmetric encipherment system" and note 1 to entry have been added.]
3.3
attack
algorithm that performs computations and that can request the encryption (3.11) and/or decryption
(3.9) of adaptively chosen texts under a single secret key (3.25)/private key (3.21), with the purpose of
recovering either the unknown plaintext (3.20) for a given ciphertext (3.7), which may be adaptively
chosen but for which a request to decrypt the ciphertext is not issued, or a secret key/private key
Note 1 to entry: Attacks are discussed in detail in Annex C.
3.4
attack cost
ratio of the average workload of the attack (3.3) to an equivalent number of calls to the encryption
algorithm (3.12) under attack multiplied by the success probability of the attack
Note 1 to entry: Using the notation defined in Clause 4, the attack cost is equal to the ratio W/P.
Note 2 to entry: Other attack cost metrics and properties, such as memory complexity, data complexity, the
ability to be accelerated by specialized hardware or parallelizability may also be important in judging the impact
of a cryp
...
INTERNATIONAL ISO/IEC
STANDARD 18033-1
Third edition
2021-09
Information security — Encryption
algorithms —
Part 1:
General
Sécurité de l'information — Algorithmes de chiffrement —
Partie 1: Généralités
Reference number
©
ISO/IEC 2021
© ISO/IEC 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO/IEC 2021 – 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 . 5
5 Nature of encryption . 5
5.1 Purpose of encryption . 5
5.2 Symmetric and asymmetric encryption systems . 6
5.3 Key management . 6
6 Use and properties of encryption . 6
6.1 General . 6
6.2 Asymmetric encryption systems . 7
6.3 Block ciphers . 7
6.3.1 General. 7
6.3.2 Modes of operation . 7
6.3.3 Message authentication codes (MACs) . 7
6.4 Stream ciphers . 8
6.5 Identity-based encryption systems . 8
6.6 Homomorphic encryption systems . 8
7 Object identifiers . 8
Annex A (informative) Criteria for submission of encryption systems for possible inclusion
in the ISO/IEC 18033 series . 9
Annex B (informative) Criteria for the deletion of encryption systems from
the ISO/IEC 18033 series .14
Annex C (informative) Attacks on encryption algorithms .15
Bibliography .18
© ISO/IEC 2021 – 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 or www .iec .ch/ members
_experts/ refdocs).
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 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. In the IEC, see www .iec .ch/ understanding -standards.
This document was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 27, Information security, cybersecurity and privacy protection.
This third edition cancels and replaces the second edition (ISO/IEC 18033-1:2015), which has been
technically revised. The main changes compared with the previous edition are as follows:
— Clause 3 has been refined;
— criteria for submission of encryption systems have been refined for possible inclusion in the
ISO/IEC 18033 series; and
— the use and security properties of encryption algorithms have been clarified.
A list of all parts in the ISO/IEC 18033 series can be found on the ISO website.
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 and www .iec .ch/ national
-committees.
iv © ISO/IEC 2021 – All rights reserved
Introduction
The ISO/IEC 18033 series specifies encryption systems for the purpose of data confidentiality. The
inclusion of encryption systems in this document is intended to promote their use as reflecting the
current state of the art in encryption systems.
The primary purpose of encryption systems is to protect the confidentiality of stored or transmitted
data. An encryption algorithm is applied to data (often called plaintext) to yield encrypted data (or
ciphertext). This process is known as encryption. The encryption algorithm should be designed so that
the ciphertext yields no information about the plaintext except, perhaps, its length. Associated with
every encryption algorithm is a corresponding decryption algorithm, which transforms ciphertext
back into its original plaintext.
Encryption systems work in association with a key. In a symmetric encryption system, the same key is
used in both the encryption and decryption algorithms. In an asymmetric encryption system, different
but related keys are used for encryption and decryption. ISO/IEC 18033-2 and ISO/IEC 18033-5 focus
on two different classes of asymmetric encryption systems, known as conventional asymmetric
encryption systems (or just asymmetric encryption systems), and identity-based encryption systems.
ISO/IEC 18033-3 and ISO/IEC 18033-4 focus on two different classes of symmetric encryption systems,
known as block ciphers and stream ciphers. ISO/IEC 18033-6 focuses on a specific class of encryption
systems called homomorphic.
© ISO/IEC 2021 – All rights reserved v
INTERNATIONAL STANDARD ISO/IEC 18033-1:2021(E)
Information security — Encryption algorithms —
Part 1:
General
1 Scope
This document is general in nature and provides definitions that apply in subsequent parts of the
ISO/IEC 18033 series.
It introduces the nature of encryption and describes certain general aspects of its use and properties.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 18033-2, Information technology — Security techniques — Encryption algorithms — Part 2:
Asymmetric ciphers
ISO/IEC 18033-3, Information technology — Security techniques — Encryption algorithms — Part 3: Block
ciphers
ISO/IEC 18033-4, Information technology — Security techniques — Encryption algorithms — Part 4:
Stream ciphers
ISO/IEC 18033-5, Information technology — Security techniques — Encryption algorithms — Part 5:
Identity-based ciphers
ISO/IEC 18033-6, IT Security techniques — Encryption algorithms — Part 6: Homomorphic encryption
ISO/IEC 18033-7, Information technology — Security techniques — Encryption algorithms — Part 7:
Tweakable block ciphers
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
asymmetric cryptographic technique
cryptographic technique that uses two related transformations, a public transformation [defined by
the public key (3.22)] and a private transformation [defined by the private key (3.21)]
Note 1 to entry: The two transformations have the property that, given the public transformation, it is
computationally infeasible to derive the private transformation. Computational feasibility depends on the
specific security requirements and environment.
[SOURCE: ISO/IEC 11770-1:2010, 2.1, modified — The last sentence in note 1 to entry has been added.]
© ISO/IEC 2021 – All rights reserved 1
3.2
asymmetric encryption system
asymmetric cipher
asymmetric encipherment system
system based on asymmetric cryptographic techniques (3.1) whose public transformation is used for
encryption (3.11) and whose private transformation is used for decryption (3.9)
Note 1 to entry: A method for key (3.17) pair generation is assumed.
[SOURCE: ISO/IEC 9798-1:2010, 3.2, modified — The admitted terms "asymmetric cipher" and
"asymmetric encipherment system" and note 1 to entry have been added.]
3.3
attack
algorithm that performs computations and that can request the encryption (3.11) and/or decryption
(3.9) of adaptively chosen texts under a single secret key (3.25)/private key (3.21), with the purpose of
recovering either the unknown plaintext (3.20) for a given ciphertext (3.7), which may be adaptively
chosen but for which a request to decrypt the ciphertext is not issued, or a secret key/private key
Note 1 to entry: Attacks are discussed in detail in Annex C.
3.4
attack cost
ratio of the average workload of the attack (3.3) to an equivalent number of calls to the encryption
algorithm (3.12) under attack multiplied by the success probability of the attack
Note 1 to entry: Using the notation defined in Clause 4, the attack cost is equal to the ratio W/P.
Note 2 to entry: Other attack cost metrics and properties, such as memory complexity, data complexity, the
ability to be accelerated by specialized hardware or parallelizability may also be important in judging the impact
of a cryp
...
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