ISO/IEC 18033-5:2015

DRAFT INTERNATIONAL STANDARD
ISO/IEC DIS 18033-5
ISO/IEC JTC 1/SC 27 Secretariat: DIN
Voting begins on: Voting terminates on:
2014-07-07 2014-10-07
Information technology — Security techniques —
Encryption algorithms —
Part 5:
Identity-based ciphers
Technologies de l’information — Techniques de sécurité — Algorithmes de chiffrement —
Partie 5: Chiffrements identitaires
ICS: 35.040
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ISO/IEC DIS 18033-5:2014(E)
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PROVIDE SUPPORTING DOCUMENTATION. ISO/IEC 2014

ISO/IEC DIS 18033-5:2014(E)
Copyright notice
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ii © ISO 2014 – All rights reserved

ISO/IEC DIS 18033-5
Contents Page
Foreword . v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 3
5 Cryptographic transforms . 5
5.1 General . 5
5.2 The function IHF1 . 5
5.3 The function SHF1 . 6
5.4 The function PHF1 . 6
6 General model for identity-based encryption . 7
6.1 Composition of algorithms . 7
6.2 Plaintext length . 8
6.3 Use of labels . 8
6.4 Ciphertext format . 9
6.5 IBE operation . 9
7 General model for identity-based hybrid encryption . 10
7.1 General . 10
7.2 Identity-based key encapsulation . 10
7.2.1 Composition of algorithms . 10
7.2.2 Prefix-freeness . 11
7.3 Data encapsulation . 11
7.3.1 Composition of algorithms . 11
7.4 Identity-based hybrid encryption operation . 11
7.4.1 System parameters . 11
7.4.2 Set up . 12
7.4.3 Private key extraction . 12
7.4.4 Encryption . 12
7.4.5 Decryption . 12
8 Identity-based encryption mechanism . 13
8.1 General . 13
8.2 The BF mechanism . 13
8.2.1 Set up . 13
8.2.2 Private key extraction . 14
8.2.3 Encryption . 15
8.2.4 Decryption . 15
9 Identity-based hybrid encryption mechanisms . 16
9.1 General . 16
9.2 The SK key encapsulation mechanism . 16
9.2.1 Set up . 16
9.2.2 Private key extraction . 17
9.2.3 Session key encapsulation . 18
9.2.4 Session key de-encapsulation . 18
9.3 The BB1 key encapsulation mechanism . 18
9.3.1 Set up . 18
9.3.2 Private key extraction . 19
© ISO/IEC 2014 – All rights reserved iii

ISO/IEC DIS 18033-5
9.3.3 Session key encapsulation .20
9.3.4 Session key de-encapsulation .20
Annex A (normative) Object identifiers .22
Annex B (informative) Security considerations .25
Annex C (informative) Numerical examples .26
Annex D (informative) Mechanisms to prevent access to keys by third parties .36
Bibliography .37

iv © ISO/IEC 2014 – All rights reserved

ISO/IEC DIS 18033-5
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 18033-5 was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 27, 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
 Part 5: Identity-based ciphers
Further parts may follow.
© ISO/IEC 2014 – All rights reserved v

ISO/IEC DIS 18033-5
Introduction
Use of a public key encryption mechanism requires reliable identification of the correct public key to be used
for encryption. A public key infrastructure (PKI) provides functions to give a trusted link between an entity and
to enable the current status of the public key to be determined. In a PKI, a certification authority (CA) issues a
certificate binding a public key to the owner’s identifier together with other key specific information, e.g. the
validity period. If a public key is deemed to be invalid before its expiry date, then potential users of the public
key need to be notified, e.g. by the issue of a CA-signed Certificate Revocation List (CRL). The generation
and distribution of certificates and CRLs poses a major management problem, which the mechanisms in this
part of ISO/IEC 18033 are designed to address. On encrypting, an encryptor first obtains the CRL and checks
the current status of the certificate. Then the encryptor verifies the certificate, and finally encrypts a message.
Therefore, the encryptor has to be provided with some means of accessing the current CRL, and additionally it
should not require excessive time and computational resources for checking the validity of a certificate
whenever it encrypts a message.
Identity-based encryption (IBE) is a type of asymmetric encryption that allows a decryptor to set its public key
to an arbitrary string. By setting the public key to an easily identifiable string (e.g. an e-mail address), an
encryptor can gain assurance in its correctness without using a certificate. Moreover, if a short validity period
can be arranged, significantly shorter than the updating period of a CRL in a conventional PKI, an encryptor
can generate a ciphertext without checking the current status of the public key because revocation is unlikely
to occur during such a short period. As a result IBE is expected to reduce the certificate management
workload.
The use of IBE requires a Private Key Generator (PKG), which generates private keys for all decryptors using
its master secret key; this contrasts with ‘traditional’ asymmetric encryption mechanisms, such as those
specified in ISO/IEC 18033-2, in which entities generate their own public/private key pairs. As a result, use of
IBE is only appropriate when it is acceptable for a third party to have decryption access to all encrypted data.

The identity-based encryption mechani
...