ISO/TS 32004:2024
(Main)Document management — Portable Document Format — Integrity protection in encrypted documents in PDF 2.0
Document management — Portable Document Format — Integrity protection in encrypted documents in PDF 2.0
This document specifies how to extend the ISO 32000-2:2020 specification by adding extensions to the Encrypt dictionary and trailer dictionary to provide integrity protection to the encrypted PDF document. This document also ensures that extensions are fully backward-compatible. These extensions are intended for developers of software that creates PDF files (PDF writers), software that reads existing PDF files and (usually) interprets their contents for display (PDF readers), software that reads and displays PDF content and interacts with the computer users to possibly modify and save the PDF file (interactive PDF processors) and PDF products that read and/or write PDF files for a variety of other purposes (PDF processors). NOTE PDF writers and PDF readers are more specialized classifications of interactive PDF processors and both are PDF processors. This document does not specify the following: — specific processes for converting paper or electronic documents to the PDF file format; — specific technical design, user interface implementation, or operational details of rendering; — specific physical methods of storing these documents such as media and storage conditions; — methods for validating the conformance of PDF files or PDF processors; — required computer hardware and/or operating system.
Gestion des documents — Format de document portable — Protection de l'intégrité dans les documents chiffrés en PDF 2.0
General Information
Standards Content (Sample)
Technical
Specification
ISO/TS 32004
First edition
Document management — Portable
2024-04
Document Format — Integrity
protection in encrypted documents
in PDF 2.0
Gestion des documents — Format de document portable —
Protection de l'intégrité dans les documents chiffrés en PDF 2.0
Reference number
© ISO 2024
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
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and Definitions . 2
4 Extension schema details . 3
5 Proposed changes . 3
5.1 Encrypt dictionary .3
5.1.1 Additions to ISO 32000-2:2020, 7.6.2 .3
5.1.2 Additions to ISO 32000-2:2020, 7.6.4.2 .3
5.1.3 Additions to ISO 32000-2:2020, 7.6.5.2 .4
5.2 File trailer .4
5.2.1 Additions to ISO 32000-2:2020, 7.5.5 .4
5.2.2 Additions to ISO 32000-2:2020, 7.6.2 .4
5.2.3 AuthCode dictionary .4
6 Composing PDF MAC tokens. 6
6.1 General .6
6.2 PdfMacIntegrityInfo data type .6
6.3 CMS structure of a PDF MAC token .6
6.3.1 General .6
6.3.2 Encapsulated content info of a PDF MAC token .6
6.3.3 Recipient info object, MAC key generation and key encryption .6
6.3.4 Digest algorithm identification .7
6.3.5 MAC algorithm identification.7
6.3.6 Authenticated attributes .7
6.3.7 Unauthenticated attributes .8
6.4 Key derivation function .8
6.5 Location of PDF MAC tokens.9
6.5.1 Location of a PDF MAC token in an unsigned revision .9
6.5.2 Location of a PDF MAC token in a signed revision .9
6.6 Computing the digests in a PDF MAC token .9
6.6.1 General .9
6.6.2 PDF MAC digests in unsigned revisions .10
6.6.3 PDF MAC digests in signed revisions .10
Annex A (informative) ASN.1 module for PDF MAC .11
Annex B (informative) Validation of document integrity using PDF MAC .12
Annex C (informative) Examples . 14
Bibliography .16
iii
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.
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 ISO 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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/TC 171, Document management applications,
Subcommittee SC 2, Document file formats, EDMS systems and authenticity of information.
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
Introduction
When encrypting documents, it is important to not only preserve the confidentiality of the encrypted
material, but also to ensure that the receiving party can verify its integrity. Encryption mechanisms defined
in ISO 32000-2:2020 currently only provide confidentiality without this authentication aspect.
This document describes a mechanism to protect the integrity of an encrypted PDF document using a
Message Authentication Code (MAC), with key material derived from the file encryption key. Message
authentication codes are distinct from digital signatures based on public-key cryptography. Digital
signatures and message authentication codes have different but complementary security properties: a
valid MAC created following this document proves knowledge of the file encryption key, whereas digital
signatures as defined in ISO 32000-2:2020 do not have that property.
The MAC mechanism described in this document is backwards compatible with ISO 32000-2:2020 and can
also be used in PDF documents containing digital signatures.
This document follows the lexical conventions regarding the usage of bold and italics which are specified in
ISO 32000-2:2020, Clause 4.
v
Technical Specification ISO/TS 32004:2024(en)
Document management — Portable Document Format —
Integrity protection in encrypted documents in PDF 2.0
1 Scope
This document specifies how to extend the ISO 32000-2:2020 specification by adding extensions to the
Encrypt dictionary and trailer dictionary to provide integrity protection to the encrypted PDF document.
This document also ensures that extensions are fully backward-compatible.
These extensions are intended for developers of software that creates PDF files (PDF writers), software
that reads existing PDF files and (usually) interprets their contents for display (PDF readers), software that
reads and displays PDF content and interacts with the computer users to possibly modify and save the PDF
file (interactive PDF processors) and PDF products that read and/or write PDF files for a variety of other
purposes (PDF processors).
NOTE PDF writers and PDF readers are more specialized classifications of interactive PDF processors and both
are PDF processors.
This document does not specify the following:
— specific processes for converting paper or electronic documents to the PDF file format;
— specific technical design, user interface implementation, or operational details of rendering;
— specific physical methods of storing these documents such as media and storage conditions;
— methods for validating the conformance of PDF files or PDF processors;
— required computer hardware and/or operating system.
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 32000-2:2020, Document management — Portable document format — Part 2: PDF 2.0
1)
IETF RFC 2104, HMAC: Keyed-Hashing for Message Authentication. [online]. 1997.
IETF RFC 4231, Identifiers and Test Vectors for HMAC-SHA-224, HMAC-SHA-256, HMAC-SHA-384, and HMAC-
2)
SHA-512. [online]. 2005
3)
IETF RFC 3394, Advanced Encryption Standard (AES) Key Wrap Algorithm. [online]
4)
IETF RFC 5652:2009, Cryptographic Message Syntax (CMS). [online]. 2009
5)
IETF RFC 5869, HMAC-based Extract-and-Expand Key Derivation Function (HKDF). [online]. 2010
1) https:// tools .ietf .org/ html/ rfc2104 .html
2) https:// tools .ietf .org/ html/ rfc4231
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.