ISO/IEC 18033-1:2005

INTERNATIONAL ISO/IEC
STANDARD 18033-1
First edition
2005-02-01


Information technology — Security
techniques — Encryption algorithms —
Part 1:
General
Technologies de l'information — Techniques de sécurité — Algorithmes
de chiffrement —
Partie 1: Généralités




Reference number
ISO/IEC 18033-1:2005(E)
©
ISO/IEC 2005

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ISO/IEC 18033-1:2005(E)
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ISO/IEC 18033-1:2005(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Terms and definitions. 1
3 The nature of encryption. 4
3.1 The purpose of encryption. 4
3.2 Symmetric and asymmetric ciphers . 4
3.3 Key management . 5
4 The use and properties of encryption. 5
4.1 Asymmetric ciphers. 5
4.2 Block ciphers. 5
4.2.1 Modes of operation . 5
4.2.2 Message Authentication Codes (MACs).6
4.3 Stream ciphers . 6
5 Object identifiers. 6
Annex A (informative) Criteria for inclusion of ciphers in ISO/IEC 18033 . 7
Bibliography . 8

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ISO/IEC 18033-1:2005(E)
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. In the field of information
technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC 1.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of the joint technical committee is to prepare International Standards. Draft International
Standards adopted by the joint technical committee are circulated to national bodies for voting. Publication as
an International Standard requires approval by at least 75 % of the national 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 and IEC shall not be held responsible for identifying any or all such patent rights.
ISO/IEC 18033-1 was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 27, IT Security techniques.
ISO/IEC 18033 consists of the following parts, under the general title Information technology — Security
techniques — Encryption algorithms:
 Part 1: General
 Part 2: Asymmetric ciphers
 Part 3: Block ciphers
 Part 4: Stream ciphers

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ISO/IEC 18033-1:2005(E)
Introduction
ISO/IEC 18033 is a multi-part International Standard that specifies encryption systems (ciphers) for the
purpose of data confidentiality. The inclusion of ciphers in ISO/IEC 18033 is intended to promote their use as
reflecting the current ‘state of the art’ in encryption techniques.
The primary purpose of encryption (or encipherment) techniques is to protect the confidentiality of stored or
transmitted data. An encryption algorithm is applied to data (often called plaintext or cleartext) 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.
Ciphers work in association with a key. In a symmetric cipher, the same key is used in both the encryption and
decryption algorithms. In an asymmetric cipher, different but related keys are used for encryption and
decryption. ISO/IEC 18033-2 is devoted to asymmetric ciphers. ISO/IEC 18033-3 and ISO/IEC 18033-4 are
devoted to two different classes of symmetric ciphers, known as block ciphers and stream ciphers.

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INTERNATIONAL STANDARD ISO/IEC 18033-1:2005(E)

Information technology — Security techniques — Encryption
algorithms —
Part 1:
General
1 Scope
This part of ISO/IEC 18033 is general in nature, and provides definitions that apply in subsequent parts of
ISO/IEC 18033. The nature of encryption is introduced, and certain general aspects of its use and properties
are described. The criteria used to select the algorithms specified in subsequent parts of ISO/IEC 18033 are
defined in Annex A.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
asymmetric cipher
alternative term for asymmetric encryption system.
2.2
asymmetric cryptographic technique
cryptographic technique that uses two related transformations, a public transformation (defined by the public
key) and a private transformation (defined by the private key). The two transformations have the property that,
given the public transformation, it is computationally infeasible to derive the private transformation
[ISO/IEC 11770-1:1996].
2.3
asymmetric encipherment system
alternative term for asymmetric encryption system.
2.4
asymmetric encryption system
system based on asymmetric cryptographic techniques whose public transformation is used for encryption
and whose private transformation is used for decryption [ISO/IEC 9798-1:1997].
2.5
asymmetric key pair
pair of related keys where the private key defines the private transformation and the public key defines the
public transformation [ISO/IEC 9798-1:1997].
2.6
block
string of bits of a defined length.
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ISO/IEC 18033-1:2005(E)
2.7
block cipher
symmetric encryption system with the property that the encryption algorithm operates on a block of plaintext,
i.e. a string of bits of a defined length, to yield a block of ciphertext.
2.8
cipher
alternative term for encipherment system.
2.9
ciphertext
data which has been transformed to hide its information content [ISO/IEC 10116:1997].
2.10
cleartext
alternative term for plaintext.
2.11
decipherment
alternative term for decryption.
2.12
decipherment algorithm
alternative term for decryption algorithm.
2.13
decryption
reversal of a corresponding encipherment [ISO/IEC 11770-1:1996].
2.14
decryption algorithm
process which transforms ciphertext into plaintext.
2.15
encipherment
alternative term for encryption.
2.16
encipherment algorithm
alternative term for encryption algorithm.
2.17
encipherment system
alternative term for encryption system.
2.18
encryption
(reversible) transformation of data by a cryptographic algorithm to produce ciphertext, i.e., to hide the
information content of the data [ISO/IEC 9797-1].
2.19
encryption algorithm
process which transforms plaintext into ciphertext.
2.20
encryption system
cryptographic technique used to protect the confidentiality of data, and which consists of three component
processes: an encryption algorithm, a decryption algorithm, and a method for generating keys.
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ISO/IEC 18033-1:2005(E)
2.21
key
sequence of symbols that controls the operation of a cryptographic transformation (e.g. encipherment,
decipherment) [ISO/IEC 11770-1:1996].
2.22
keystream
pseudorandom sequence of symbols, intended to be secret, used by the encryption and decryption algorithms
of a stream cipher. If a portion of the keystream is known by an attacker, then it shall be computationally
infeasible for the attacker to deduce any information about the remainder of the keystream.
2.23
n-bit block cipher
block cipher with the property that plaintext blocks and ciphertext blocks are n bits in length
[ISO/IEC 10116:1997].
2.24
plaintext
unencrypted information [ISO/IEC 10116:1997].
2.25
private key
that key of an entity’s asymmetric key pair which should only be used by that entity [ISO/IEC 11770-1:1996].
NOTE A private key should not normally be disclosed.
2.26
public key
that key of an entity’s asymmetric key pair which can be made public [ISO/IEC 11770-1:1996].
2.27
secret key
key used with symmetric cryptographic techniques by a specified set of entities [ISO/IEC 11770-3:1999].
2.28
self-synchronous stream cipher
stream cipher with the property that the keystream symbols are generated as a function of a secret key and a
fixed number of previous ciphertext bits.
2.29
synchronous stream cipher
stream cipher with the property that the keystream symbols are generated as a function of a secret key, and
are independent of the plaintext and ciphertext.
2.30
stream cipher
symmetric encryption system with the property that the encryption algorithm involves combining a sequence of
plaintext symbols with a sequence of keystream symbols one symbol at a time, using an invertible function.
Two types of stream cipher can be identified: synchronous stream ciphers and self-synchronous stream
ciphers, distinguished by the method used to obtain the keystream.
2.31
symmetric cipher
alternative term for symmetric encryption system.
2.32
symmetric cryptographic technique
cryptographic technique that uses the same secret key for both the originator’s and the recipient’s
transformation. Without knowledge of the secret key, it is computationally infeasible to compute either the
originator’s or the recipient’s transformation.
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ISO/IEC 18033-1:2005(E)
NOTE Examples of symmetric cryptographic techniques include symmetric ciphers and Message Authentication
Codes (MACs). In a symmetric cipher, the same secret key is used to encrypt and decrypt data. In a MAC scheme, the
same secret key is used to generate and verify MACs.
2.33
symmetric encipherment system
alternative term for symmetric encryption system.
2.34
symmetric encryption system
encryption system based on symmetric cryptogra
...