Health informatics -- Public key infrastructure

This document supports interchangeability of digital signatures and the prevention of incorrect or illegal digital signatures by providing minimum requirements and formats for generating and verifying digital signatures and related certificates. This document describes the common technical, operational, and policy requirements that need to be addressed to enable digital certificates to be used in protecting the exchange of healthcare information within a single domain, between domains, and across jurisdictional boundaries. Its purpose is to create a platform for global interoperability. It specifically supports digital certificate enabled communication across borders but could also provide guidance for the national or regional deployment of digital certificates in healthcare. It defines the provable compliance with a PKI policy necessary in the domain of healthcare. This document specifies a method of adopting long-term signature formats to ensure integrity and non-repudiation in long-term electronic preservation of healthcare information. This document provides Healthcare specific PKI (HPKI) profiles of digital signature based on the ETSI Standard and the profile of the ISO/ETSI Standard specified in CAdES, XAdES, and PAdES.

Informatique de la santé -- Infrastructure clé publique

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Publication Date
06-Oct-2020
Current Stage
5060 - Close of voting Proof returned by Secretariat
Start Date
14-Jul-2020
Completion Date
14-Jul-2020
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INTERNATIONAL ISO
STANDARD 17090-4
Second edition
2020-10
Health informatics — Public key
infrastructure —
Part 4:
Digital signatures for healthcare
documents
Informatique de la santé — Infrastructure clé publique —
Partie 4: Signatures numériques pour les documents des soins
médicaux
Reference number
ISO 17090-4:2020(E)
ISO 2020
---------------------- Page: 1 ----------------------
ISO 17090-4:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

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 2020 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 17090-4:2020(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definition ........................................................................................................................................................................................ 1

4 Target of application ........................................................................................................................................................................................ 2

4.1 Target system ........................................................................................................................................................................................... 2

4.2 Generation process .............................................................................................................................................................................. 3

4.3 Verification process ............................................................................................................................................................................ 4

4.3.1 General...................................................................................................................................................................................... 4

4.3.2 Verification of ES .............................................................................................................................................................. 4

4.3.3 Verification of ES-T ......................................................................................................................................................... 6

4.3.4 Verification of ES-A ........................................................................................................................................................ 7

4.4 CAdES specification .........................................................................................................................................................................12

4.4.1 General...................................................................................................................................................................................12

4.4.2 Long term signature profile ................................................................................................................................12

4.4.3 Representation of the required level ...........................................................................................................12

4.4.4 CAdES-T profile ..............................................................................................................................................................13

4.4.5 CAdES-A profile ..............................................................................................................................................................14

4.5 XAdES specification .........................................................................................................................................................................15

4.5.1 General...................................................................................................................................................................................15

4.5.2 Defined long-term signature profiles ..........................................................................................................15

4.5.3 Representation of the required level ...........................................................................................................16

4.5.4 Requirement for XAdES-T .....................................................................................................................................16

4.5.5 Requirement for XAdES-A .....................................................................................................................................18

4.6 PAdES Specification .........................................................................................................................................................................19

4.6.1 General...................................................................................................................................................................................19

4.6.2 Defined long term signature profiles ..........................................................................................................19

4.6.3 Representation of the required level ...........................................................................................................20

4.6.4 Requirement for PAdES-T ......................................................................................................................................20

4.6.5 Requirement for PAdES-A .....................................................................................................................................23

Annex A (informative) Use cases............................................................................................................................................................................24

Bibliography .............................................................................................................................................................................................................................27

© ISO 2020 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 17090-4:2020(E)
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 documents 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 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).

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 215, Health informatics.

This second edition cancels and replaces the first edition (ISO 17090-4:2014), which has been

technically revised. The main changes compared to the previous edition are as follows:

— update of the reference standard and addition of PAdES definitions.
A list of all parts in the ISO 17090 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.
iv © ISO 2020 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 17090-4:2020(E)
Introduction

The healthcare industry is faced with the challenge of reducing costs by moving from paper-based

processes to automated electronic processes. New models of healthcare delivery are emphasizing the

need for patient information to be shared among a growing number of specialist healthcare providers

and across traditional organizational boundaries.

Healthcare information concerning individual citizens is commonly interchanged by means of

electronic mail, remote database access, electronic data interchange, and other applications. The

Internet provides a highly cost-effective and accessible means of interchanging information but it

is also an insecure vehicle that demands additional measures be taken to maintain the privacy and

confidentiality of information. Threats to the security of health information through unauthorized

access (either inadvertent or deliberate) are increasing. It is essential that reliable information security

services that minimize the risk of unauthorized access be available to the healthcare system.

How does the healthcare industry provide appropriate protection for the data conveyed across the

Internet in a practical, cost-effective way? Public Key Infrastructure (PKI) and digital certificate

technology seeks to address this challenge.

The proper deployment of digital certificates requires a blend of technology, policy, and administrative

processes that enable the exchange of sensitive data in an unsecured environment by the use of public

key cryptography to protect information in transit and certificates to confirm the identity of a person

or entity. In healthcare environments, this technology uses authentication, encipherment and digital

signatures to facilitate confidential access to, and movement of, individual health records to meet

both clinical and administrative needs. The services offered by the deployment of digital certificates

(including encipherment, information integrity and digital signatures) are able to address many of

these security issues. This is especially the case if digital certificates are used in conjunction with

an accredited information security standard. Many individual organizations around the world have

started to use digital certificates for this purpose.

Interoperability of digital certificate technology and supporting policies, procedures, and practices

is of fundamental importance if information is to be exchanged between organizations and between

jurisdictions in support of healthcare applications (for example between a hospital and a community

physician working with the same patient).

Achieving interoperability between different digital certificate implementations requires the

establishment of a framework of trust, under which parties responsible for protecting an individual’s

information rights might rely on the policies and practices and, by extension, on the validity of digital

certificates issued by other established authorities.

Many countries are deploying digital certificates to support secure communications within their

national boundaries. Inconsistencies will arise in policies and procedures between the Certification

Authorities (CAs) and the Registration Authorities (RAs) of different countries if standards development

activity is restricted to within national boundaries.

Digital certificate technology is still evolving in certain aspects that are not specific to healthcare.

Important standardization efforts and, in some cases, supporting legislation are ongoing. On the

other hand, healthcare providers in many countries are already using or planning to use digital

certificates. This document seeks to address the need for guidance to support these rapid international

developments.

The Internet is increasingly used as the vehicle of choice to support the movement of healthcare data

between healthcare organizations and is the only realistic choice for cross-border communication in

this sector.

The ISO 17090 series, contributes to defining how digital certificates can be used to provide security

services in the healthcare industry, including authentication, confidentiality, data integrity, and the

technical capacity to support the quality of digital signature.
© ISO 2020 – All rights reserved v
---------------------- Page: 5 ----------------------
ISO 17090-4:2020(E)

This document is in line with ISO/ETSI standards for long-term signature formats to improve and

guarantee interoperability in the healthcare field.

There is no limitation regarding the data format and the subject for which the signature is created.

vi © ISO 2020 – All rights reserved
---------------------- Page: 6 ----------------------
INTERNATIONAL STANDARD ISO 17090-4:2020(E)
Health informatics — Public key infrastructure —
Part 4:
Digital signatures for healthcare documents
1 Scope

This document supports interchangeability of digital signatures and the prevention of incorrect or

illegal digital signatures by providing minimum requirements and formats for generating and verifying

digital signatures and related certificates.

This document describes the common technical, operational, and policy requirements that need to be

addressed to enable digital certificates to be used in protecting the exchange of healthcare information

within a single domain, between domains, and across jurisdictional boundaries. Its purpose is to create

a platform for global interoperability. It specifically supports digital certificate enabled communication

across borders but could also provide guidance for the national or regional deployment of digital

certificates in healthcare.

It defines the provable compliance with a PKI policy necessary in the domain of healthcare. This

document specifies a method of adopting long-term signature formats to ensure integrity and non-

repudiation in long-term electronic preservation of healthcare information.

This document provides Healthcare specific PKI (HPKI) profiles of digital signature based on the ETSI

Standard and the profile of the ISO/ETSI Standard specified in CAdES, XAdES, and PAdES.

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 17090-1, Health informatics — Public key infrastructure — Part 1: Overview of digital certificate

services
3 Terms and definition

For the purposes of this document, the terms and definitions given in ISO 17090-1 and the following apply.

ISO and IEC maintain terminological 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
certification path

connection of a series of certificates binding the certificate that is to be validated to a trusted root

trust anchor
3.2
certification path validation

path to be validated to a trusted root trust anchor including revocation checking

© ISO 2020 – All rights reserved 1
---------------------- Page: 7 ----------------------
ISO 17090-4:2020(E)
3.3
hash value

value calculated by a hash function, which is a computation method used to generate a random value of

fixed length from the data of any optional length
4 Target of application
4.1 Target system
The target systems of this document are as follows:

a) the digital signature library with the digital signature function and the digital signature verification

function for the medical treatment application;

b) the digital signature program and the digital signature verification program as the stand-alone

software or with the medical treatment application;
The following are out of the scope of application:

a) the medical treatment application that does not process the digital signature data directly;

b) the medical treatment application that processes the digital signature and the result of signature

verification with the digital signature library, the specific digital signature program, or the specific

digital signature verification program;

c) the application interface and user interface; Figure 1 shows an example of the processing layer.

The digital signature application layer (the digital signature library, the digital signature program,

or the digital signature verification program) is the target scope of this example. Therefore, the

following layer, CSP, and PKCS#11, is not within the targeted scope of this document.

In HPKI, it is assumed that storage modules of the end entity subscriber private key conform to

standards of levels equal to or higher than US FIPS 140-2 level 1. Also, in addition to the smart card, as

illustrated in Figure 1, a system could use a USB token, software token, etc. as the medium that stores

the private key.
2 © ISO 2020 – All rights reserved
---------------------- Page: 8 ----------------------
ISO 17090-4:2020(E)
Figure 1 — Example of processing layer digital signature specification
4.2 Generation process

The digital signature format is based on ETSI advanced digital signatures, where CAdES (CMS Advanced

[8] [9]

Digital Signature) and XAdES (XML Advanced Digital Signature) are described in this document.

These specifications define the various formats according to purpose of operation.

— ES: The format that has the digital signature value, data itself, and information about the signer.

— ES-T: The format that has the signature timestamp in addition to the ES format. Signature timestamp

is a trusted timestamp provided by a timestamp authority to prove the existence of the signature.

— ES-C: The format that has validation data references in addition to the ES-T format.

— ES-X: The format that has ES-C timestamp to protect validation data references.

— ES-X Long: The format that has the ES-C format and revocation information for verification.

— ES-A: The format that has an archive timestamp to protect the signature, the timestamps, and the

validation data.
© ISO 2020 – All rights reserved 3
---------------------- Page: 9 ----------------------
ISO 17090-4:2020(E)
See Figure 2 for the different format types of digital signature.
Figure 2 — Format types of digital signature

These specifications only define the profile of ES-T and ES-A. The other formats (ES-C, ES-X, ES-X Long)

are considered to be intermediate formats to generate ES-T or ES-A. So they are not included in this

document.
[8]

The digital signature format is based on ETSI advanced digital signatures, where CAdES based on a

[9]

CMS (Cryptographic Message Syntax) and XAdES based on an XML Advanced Digital signature are

described in this document.

Subclause 4.4 describes the CAdES profile that specifies elements required/allowed to generate ES-T

and ES-A. Subclause 4.5 describes the XAdES profile of ES-T and ES-A.
4.3 Verification process
4.3.1 General

Subclause 4.3 describes an overview of the basic verification processes. This document does not provide

verification methods for optional attributes. If the signature data contains any optional attributes, the

optional attributes should be correctly verified in accordance with other specifications, policies, or

guidelines.
4.3.2 Verification of ES
4.3.2.1 Verification processes of ES

The verification processes of ES are described below, and the order of the processes should not be

changed. See Figure 3.
Figure 3 — Verification processes of ES
4 © ISO 2020 – All rights reserved
---------------------- Page: 10 ----------------------
ISO 17090-4:2020(E)
a) Verify the format of the signing data.
Verify if the digital signature format is correct.
b) Verify the signer’s certificate.

The following steps are performed to ascertain the validity of the signer’s certificate.

[10]
1) Certification path validation described in RFC5280 .

2) Verify signer’s certificate extensions regarding HPKI as stated in ISO 17090-1

c) Verify the signature value of the signer identifier.
The following steps are performed.
1) Verify the signature value using the signer’s public key.
2) Verify the identifier of the signer’s certificate.
The above processes are explained in Annex A.
4.3.2.2 Description of verification processes
Verification process Description
a) Ascertain correctness of format. The following conditions shall be checked.
— If the structure of the signature data conforms to the
defined format.
— If the signature data contains all elements required in
the profile.
— If the version number of the signature data are correct.

b) Verify the signer’s certificate. 1) Certification path validation described in RFC5280.

— Build and verify the certification path for the
signer’s certificate.
2) Ascertain extensions regarding HPKI contained in the
signer’s certificate.
— Implementations are required to support
functions to check the following elements.
— HPKI certificate policy identifier.
— The value of the hcRole attribute in the signer’s
certificate.
— The ascertainment method not covered by
this document. It is possible to choose suitable
methods for applications.
© ISO 2020 – All rights reserved 5
---------------------- Page: 11 ----------------------
ISO 17090-4:2020(E)
Verification process Description

c) Verify the signature value and signer identifier. 1) Verify the signature value using the signer’s public key.

The following steps shall be performed.
— Calculate the hash value of the content data and
ascertain that it matches the value of the message
digest contained in the signature.
— Verify the signature value with signed attributes using
the signer’s public key.
2) Verify the correspondence of the identifier
information of the signer’s certificate.
— Ascertain that the signer identifier matches the
signer’s certificate attributes contained in the
signature data.
4.3.3 Verification of ES-T
4.3.3.1 Verification process of ES-T
This section describes the process to verify a signature in ES-T format.

The verification processes of ES-T are described below, and the order of the processes should not be

changed. See Figure 4.
Figure 4 — Verification processes of ES-T
a) Verify the signature timestamp.
1) Verify the certificate of the TSA that provides the signature timestamp.
2) Verify the signature value of the TSA that provides the signature timestamp.
3) Verify the message imprint of the timestamp token.
b) Verify the signer’s signature at the time of the signature timestamp.

1) Ascertain that the signer’s signature was valid at the time of the signature timestamp.

6 © ISO 2020 – All rights reserved
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ISO 17090-4:2020(E)
2) Ascertain that the signer’s trust anchor is appropriate.
The above processes are explained in Annex A.
4.3.3.2 Description of a verification process
Verification process Description

a) Verify the signature timestamp. 1) Verify the certificate of the TSA that provides the

signature timestamp.
The following steps shall be performed for the TSA certificate.
— Certification path validation as described in RFC5280.
— Ascertain that the certificate contains extended key
usage for TSA purpose.
2) Verify the signature of the TSA that provides the
signature timestamp.
Verify the signature value of the timestamp token using
the public key of a TSA certificate.
3) Verify the message imprint of the timestamp token.
— Calculate the hash value of the signer’s signature
value and ascertain that it matches the value of
the message imprint within the timestamp token.

b) Verify the ES at the time of the signature 1) Verify the ES at the time of the signature timestamp.

timestamp.
— Verify that the certificate of the signer was valid
at the time of the signature timestamp.
2) Verify that the trust anchor is appropriate.
— Verification could be performed in a long period
of time after the ES-T data were created. The trust
anchor that was valid at the time of signature
might be expired or compromised at the time of
verification. In this case, the verifier shall verify
that the trust anchor is appropriate.
— For example, the signer and the verifier specify an
agreement about the trust anchor (for example, the
signature policy) and manage it under protection
against CA compromise, or the verifier refers to
a trusted third party that manages the history of
verification information of certificates. Specific
methods are out of the scope of this document.
4.3.4 Verification of ES-A
4.3.4.1 Verification process of ES-A

The verification processes of ES-A are described below, and the order of the processes should not be

changed. See Figure 5.
© ISO 2020 – All rights reserved 7
---------------------- Page: 13 ----------------------
ISO 17090-4:2020(E)
Figure 5 — Verification processes of ES-A
a) Verify the latest archive timestamp.
Verify that the latest archive timestamp is valid at the time of verification.
1) Verify the certificate of the TSA that provides the latest archive timestamp.
2) Verify the signature of the TSA that provides the latest archive timestamp.

3) Verify the correspondence of the latest archive timestamp and the target data of the timestamp.

b) Verify the previous archive timestamps, if present.
Verify that the timestamp was valid at the time when the data was archived.
1) Verify the certificate of the TSA that provides the archive timestamp.
2) Verify the signature of the TSA that provides archive timestamp

3) Verify the correspondence of the archive timestamp and the target data of the timestamp.

4) Verify that the trust anchor of the archive timestamp is appropriate.
c) Verify the validation data of the signer’s certificate.
1) Verify the validity of the certificate chain archived in the validation data.
2) Verify that the trust anchor is appropriate.
3) Verify the validity of revoke information archived in the validation data.
8 © ISO 2020 – All rights reserved
---------------------- Page: 14 ----------------------
ISO 17090-4:2020(E)
4) Verify that the trust anchor of revoke information is appropriate.
d) Verify the signature timestamp.
Verify that the timestamp is appropriate.
1) Verify that the signature timestamp was valid at the time it was archived.
2) Verify that the trust anchor of the signature timestamp is appropriate.
e) Verify the ES at the time of the signature timestamp.
1) Verify that the ES was valid at the time of the signature timestamp.
2) Verify that the trust anchor is appropriate.

f) Verify the ordering of the times of timestamps and the issued time of validation data.

The above processes are explained in Annex A.
4.3.4.2 Description of verification process
Verification process Description

a) Verify the latest archive timestamp 1) Verify the certificate of the TSA that provided the

latest archive timestamp.
The following steps shall be performed for the TSA certificate.
— Verify the validity of the certificate at the time of
verification.
— Ascertain that the purpose of the key usage of the TSA
certificate is appropriate.
2) Verify the signature of the TSA that provides the latest
signature timestamp.
— Verify the signature value of the timestamp token
using the public key of the TSA certificate.
3) Verify the message imprint of the timestamp token.
— Calculate the hash value of the target fields for the
archive and verify that it matches the value of the
message imprint within the timestamp token.
© ISO 2020 – All rights reserved 9
---------------------- Page: 15 ----------------------
ISO 17090-4:2020(E)
Verification process Description

b) Verify the previous archive timestamp, if it is 1) Verify the certificate of the T

...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 17090-4
ISO/TC 215
Health informatics — Public key
Secretariat: ANSI
infrastructure —
Voting begins on:
2020-06-19
Part 4:
Voting terminates on:
Digital signatures for healthcare
2020-08-14
documents
Informatique de la santé — Infrastructure clé publique —
Partie 4: Signatures numériques pour les documents des soins
médicaux
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/FDIS 17090-4:2020(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN-
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. ISO 2020
---------------------- Page: 1 ----------------------
ISO/FDIS 17090-4:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

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 2020 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/FDIS 17090-4:2020(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definition ........................................................................................................................................................................................ 1

4 Target of application ........................................................................................................................................................................................ 2

4.1 Target system ........................................................................................................................................................................................... 2

4.2 Generation process .............................................................................................................................................................................. 3

4.3 Verification process ............................................................................................................................................................................ 4

4.3.1 General...................................................................................................................................................................................... 4

4.3.2 Verification of ES .............................................................................................................................................................. 4

4.3.3 Verification of ES-T ......................................................................................................................................................... 6

4.3.4 Verification of ES-A ........................................................................................................................................................ 7

4.4 CAdES specification .........................................................................................................................................................................12

4.4.1 General...................................................................................................................................................................................12

4.4.2 Long term signature profile ................................................................................................................................12

4.4.3 Representation of the required level ...........................................................................................................12

4.4.4 CAdES-T profile ..............................................................................................................................................................13

4.4.5 CAdES-A profile ..............................................................................................................................................................14

4.5 XAdES specification .........................................................................................................................................................................15

4.5.1 General...................................................................................................................................................................................15

4.5.2 Defined long-term signature profiles ..........................................................................................................15

4.5.3 Representation of the required level ...........................................................................................................16

4.5.4 Requirement for XAdES-T .....................................................................................................................................16

4.5.5 Requirement for XAdES-A .....................................................................................................................................18

4.6 PAdES Specification .........................................................................................................................................................................19

4.6.1 General...................................................................................................................................................................................19

4.6.2 Defined long term signature profiles ..........................................................................................................19

4.6.3 Representation of the required level ...........................................................................................................20

4.6.4 Requirement for PAdES-T ......................................................................................................................................20

4.6.5 Requirement for PAdES-A .....................................................................................................................................23

Annex A (informative) Use cases............................................................................................................................................................................24

Bibliography .............................................................................................................................................................................................................................27

© ISO 2020 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO/FDIS 17090-4:2020(E)
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 documents 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 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).

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 215, Health informatics.

This second edition cancels and replaces the first edition (ISO 17090-4:2014), which has been

technically revised. The main changes compared to the previous edition are as follows:

— update of the reference standard and addition of PAdES definition.
A list of all parts in the ISO 17090 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.
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Introduction

The healthcare industry is faced with the challenge of reducing costs by moving from paper-based

processes to automated electronic processes. New models of healthcare delivery are emphasizing the

need for patient information to be shared among a growing number of specialist healthcare providers

and across traditional organizational boundaries.

Healthcare information concerning individual citizens is commonly interchanged by means of

electronic mail, remote database access, electronic data interchange, and other applications. The

Internet provides a highly cost-effective and accessible means of interchanging information but it

is also an insecure vehicle that demands additional measures be taken to maintain the privacy and

confidentiality of information. Threats to the security of health information through unauthorized

access (either inadvertent or deliberate) are increasing. It is essential that reliable information security

services that minimize the risk of unauthorized access be available to the healthcare system.

How does the healthcare industry provide appropriate protection for the data conveyed across the

Internet in a practical, cost-effective way? Public Key Infrastructure (PKI) and digital certificate

technology seeks to address this challenge.

The proper deployment of digital certificates requires a blend of technology, policy, and administrative

processes that enable the exchange of sensitive data in an unsecured environment by the use of public

key cryptography to protect information in transit and certificates to confirm the identity of a person

or entity. In healthcare environments, this technology uses authentication, encipherment and digital

signatures to facilitate confidential access to, and movement of, individual health records to meet

both clinical and administrative needs. The services offered by the deployment of digital certificates

(including encipherment, information integrity and digital signatures) are able to address many of

these security issues. This is especially the case if digital certificates are used in conjunction with

an accredited information security standard. Many individual organizations around the world have

started to use digital certificates for this purpose.

Interoperability of digital certificate technology and supporting policies, procedures, and practices

is of fundamental importance if information is to be exchanged between organizations and between

jurisdictions in support of healthcare applications (for example between a hospital and a community

physician working with the same patient).

Achieving interoperability between different digital certificate implementations requires the

establishment of a framework of trust, under which parties responsible for protecting an individual’s

information rights might rely on the policies and practices and, by extension, on the validity of digital

certificates issued by other established authorities.

Many countries are deploying digital certificates to support secure communications within their

national boundaries. Inconsistencies will arise in policies and procedures between the Certification

Authorities (CAs) and the Registration Authorities (RAs) of different countries if standards development

activity is restricted to within national boundaries.

Digital certificate technology is still evolving in certain aspects that are not specific to healthcare.

Important standardization efforts and, in some cases, supporting legislation are ongoing. On the

other hand, healthcare providers in many countries are already using or planning to use digital

certificates. This document seeks to address the need for guidance to support these rapid international

developments.

The Internet is increasingly used as the vehicle of choice to support the movement of healthcare data

between healthcare organizations and is the only realistic choice for cross-border communication in

this sector.

The ISO 17090 series, contributes to defining how digital certificates can be used to provide security

services in the healthcare industry, including authentication, confidentiality, data integrity, and the

technical capacity to support the quality of digital signature.
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This document is in line with ISO/ETSI standards for long-term signature formats to improve and

guarantee interoperability in the healthcare field.

There is no limitation regarding the data format and the subject for which the signature is created.

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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 17090-4:2020(E)
Health informatics — Public key infrastructure —
Part 4:
Digital signatures for healthcare documents
1 Scope

This document supports interchangeability of digital signatures and the prevention of incorrect or

illegal digital signatures by providing minimum requirements and formats for generating and verifying

digital signatures and related certificates.

This document describes the common technical, operational, and policy requirements that need to be

addressed to enable digital certificates to be used in protecting the exchange of healthcare information

within a single domain, between domains, and across jurisdictional boundaries. Its purpose is to create

a platform for global interoperability. It specifically supports digital certificate enabled communication

across borders but could also provide guidance for the national or regional deployment of digital

certificates in healthcare.

It defines the provable compliance with a PKI policy necessary in the domain of healthcare. This

document specifies a method of adopting long-term signature formats to ensure integrity and non-

repudiation in long-term electronic preservation of healthcare information.

This document provides Healthcare specific PKI (HPKI) profiles of digital signature based on the ETSI

Standard and the profile of the ISO/ETSI Standard specified in CAdES, XAdES, and PAdES.

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 17090-1, Health informatics — Public key infrastructure — Part 1: Overview of digital certificate

services
3 Terms and definition

For the purposes of this document, the terms and definitions given in ISO 17090-1 and the following apply.

ISO and IEC maintain terminological 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
certification path

connection of a series of certificates binding the certificate that is to be validated to a trusted root

trust anchor
3.2
certification path validation

path to be validated to a trusted root trust anchor including revocation checking

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3.3
hash value

value calculated by a hash function, which is a computation method used to generate a random value of

fixed length from the data of any optional length
4 Target of application
4.1 Target system
The target systems of this document are as follows:

a) the digital signature library with the digital signature function and the digital signature verification

function for the medical treatment application;

b) the digital signature program and the digital signature verification program as the stand-alone

software or with the medical treatment application;
The following are out of the scope of application:

a) the medical treatment application that does not process the digital signature data directly;

b) the medical treatment application that processes the digital signature and the result of signature

verification with the digital signature library, the specific digital signature program, or the specific

digital signature verification program;

c) the application interface and user interface; Figure 1 shows an example of the processing layer.

The digital signature application layer (the digital signature library, the digital signature program,

or the digital signature verification program) is the target scope of this example. Therefore, the

following layer, CSP, and PKCS#11, is not within the targeted scope of this document.

In HPKI, it is assumed that storage modules of the end entity subscriber private key conform to

standards of levels equal to or higher than US FIPS 140-2 level 1. Also, in addition to the smart card, as

illustrated in Figure 1, a system could use a USB token, software token, etc. as the medium that stores

the private key.
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Figure 1 — Example of processing layer digital signature specification
4.2 Generation process

The digital signature format is based on ETSI advanced digital signatures, where CAdES (CMS Advanced

[5] [6]

Digital Signature) and XAdES (XML Advanced Digital Signature) are described in this document.

These specifications define the various formats according to purpose of operation.

— ES: The format that has the digital signature value, data itself, and information about the signer.

— ES-T: The format that has the signature timestamp in addition to the ES format. Signature timestamp

is a trusted timestamp provided by a timestamp authority to prove the existence of the signature.

— ES-C: The format that has validation data references in addition to the ES-T format.

— ES-X: The format that has ES-C timestamp to protect validation data references.

— ES-X Long: The format that has the ES-C format and revocation information for verification.

— ES-A: The format that has an archive timestamp to protect the signature, the timestamps, and the

validation data.
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See Figure 2 for the different format types of digital signature.
Figure 2 — Format types of digital signature

These specifications only define the profile of ES-T and ES-A. The other formats (ES-C, ES-X, ES-X Long)

are considered to be intermediate formats to generate ES-T or ES-A. So they are not included in this

document.
[5]

The digital signature format is based on ETSI advanced digital signatures, where CAdES based on a

[6]

CMS (Cryptographic Message Syntax) and XAdES based on an XML Advanced Digital signature are

described in this document.

Subclause 4.4 describes the CAdES profile that specifies elements required/allowed to generate ES-T

and ES-A. Clause 4.5 describes the XAdES profile of ES-T and ES-A.
4.3 Verification process
4.3.1 General

Subclause 4.3 describes an overview of the basic verification processes. This document does not provide

verification methods for optional attributes. If the signature data contains any optional attributes, the

optional attributes should be correctly verified in accordance with other specifications, policies, or

guidelines.
4.3.2 Verification of ES
4.3.2.1 Verification processes of ES

The verification processes of ES are described below, and the order of the processes should not be

changed. See Figure 3.
Figure 3 — Verification processes of ES
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a) Verify the format of the signing data.
Verify if the digital signature format is correct.
b) Verify the signer’s certificate.

The following steps are performed to ascertain the validity of the signer’s certificate.

[10]
1) Certification path validation described in RFC5280 .

2) Verify signer’s certificate extensions regarding HPKI as stated in ISO 17090-1

c) Verify the signature value of the signer.
The following steps are performed.
1) Verify the signature value using the signer’s public key.
2) Verify the identifier of the signer’s certificate.
The above processes are explained in Annex A.
4.3.2.2 Description of verification processes
Verification process Description
a) Ascertain correctness of format. The following conditions shall be checked.
— If the structure of the signature data conforms to the
defined format.
— If the signature data contains all elements required in
the profile.
— If the version number of the signature data are correct.

b) Verify the signer’s certificate. 1) Certification path validation described in RFC5280.

— Build and verify the certification path for the
signer’s certificate.
2) Ascertain extensions regarding HPKI contained in the
signer’s certificate.
— Implementations are required to support
functions to check the following elements.
— HPKI certificate policy identifier.
— The value of the hcRole attribute in the signer’s
certificate.
— The ascertainment method not covered by
this document. It is possible to choose suitable
methods for applications.
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Verification process Description

c) Verify the signature value and signer identifier. 1) Verify the signature value using the signer’s public key.

The following steps shall be performed.
— Calculate the hash value of the content data and
ascertain that it matches the value of the message
digest contained in the signature.
— Verify the signature value with signed attributes using
the signer’s public key.
2) Verify the correspondence of the identifier
information of the signer’s certificate.
— Ascertain that the signer identifier matches the
signer’s certificate attributes contained in the
signature data.
4.3.3 Verification of ES-T
4.3.3.1 Verification process of ES-T
This section describes the process to verify a signature in ES-T format.

The verification processes of ES-T are described below, and the order of the processes should not be

changed. See Figure 4.
Figure 4 — Verification processes of ES-T
a) Verify the signature timestamp.
1) Verify the certificate of the TSA that provides the signature timestamp.
2) Verify the signature value of the TSA that provides the signature timestamp.
3) Verify the message imprint of the timestamp token.
b) Verify the signer’s signature at the time of the signature timestamp.

1) Ascertain that the signer’s signature was valid at the time of the signature timestamp.

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2) Ascertain that the signer’s trust anchor is appropriate.
The above processes are explained in Annex A.
4.3.3.2 Description of a verification process
Verification process Description

a) Verify the signature timestamp. 1) Verify the certificate of the TSA that provides the

signature timestamp.
The following steps shall be performed for the TSA
c e r t i f ic a t e .
— Certification path validation as described in RFC5280.
— Ascertain that the certificate contains extended key
usage for TSA purpose.
2) Verify the signature of the TSA that provides the
signature timestamp.
Verify the signature value of the timestamp token using
the public key of a TSA certificate.
3) Verify the message imprint of the timestamp token.
— Calculate the hash value of the signer’s signature
value and ascertain that it matches the value of
the message imprint within the timestamp token.

b) Verify the ES at the time of the signature 1) Verify the ES at the time of the signature timestamp.

timestamp.
— Verify that the certificate of the signer was valid
at the time of the signature timestamp.
2) Verify that the trust anchor is appropriate.
— Verification could be performed in a long period
of time after the ES-T data were created. The trust
anchor that was valid at the time of signature
might be expired or compromised at the time of
verification. In this case, the verifier shall verify
that the trust anchor is appropriate.
— For example, the signer and the verifier specify an
agreement about the trust anchor (for example, the
signature policy) and manage it under protection
against CA compromise, or the verifier refers to
a trusted third party that manages the history of
verification information of certificates. Specific
methods are out of the scope of this document.
4.3.4 Verification of ES-A
4.3.4.1 Verification process of ES-A

The verification processes of ES-A are described below, and the order of the processes should not be

changed. See Figure 5.
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Figure 5 — Verification processes of ES-A
a) Verify the latest archive timestamp.
Verify that the latest archive timestamp is valid at the time of verification.
1) Verify the certificate of the TSA that provides the latest archive timestamp.
2) Verify the signature of the TSA that provides the latest archive timestamp.

3) Verify the correspondence of the latest archive timestamp and the target data of the timestamp.

b) Verify the previous archive timestamps, if present.
Verify that the timestamp was valid at the time when the data was archived.
1) Verify the certificate of the TSA that provides the archive timestamp.
2) Verify the signature of the TSA that provides archive timestamp

3) Verify the correspondence of the archive timestamp and the target data of the timestamp.

4) Verify that the trust anchor of the archive timestamp is appropriate.
c) Verify the validation data of the signer’s certificate.
1) Verify the validity of the certificate chain archived in the validation data.
2) Verify that the trust anchor is appropriate.
3) Verify the validity of revoke information archived in the validation data.
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4) Verify that the trust anchor of revoke information is appropriate.
d) Verify the signature timestamp.
Verify that the timestamp is appropriate.
1) Verify that the signature timestamp was valid at the time it was archived.
2) Verify that the trust anchor of the signature timestamp is appropriate.
e) Verify the ES at the time of the signature timestamp.
1) Verify that the ES was valid at the time of the signature timestamp.
2) Verify that the trust anchor is appropriate.

f) Verify the ordering of the times of timestamps and the issued time of validation data.

The above processes are explained in Annex A.
4.3.4.2 Description of verification process
Verification process Description

a) Verify the latest archive timestamp 1) Verify the certificate of the TSA that provided the

latest archive timestamp.
The following steps shall be performed for the TSA
c e r t i f ic a t e .
— Verify the validity of the certificate at the time of
verification.
— Ascertain that the purpose of the key usage
...

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