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Public Key Infrastructure (PKI)

5.1 Overview

While Public Key Infrastructure (PKI) applications only constitute a small percentage of authentication solutions currently in use, it is expected that PKI will play a greater role in authentication in the future. PKI is also a complex area. The remaining sections of this guide focus on PKI in order to cover the relevant material comprehensively. This should not be interpreted as placing undue emphasis on PKI solutions.

PKI enables users of a basically unsecured public network such as the Internet to securely exchange information through the use of public and private cryptographic key pairs that are obtained and shared through a trusted evaluated infrastructure.

The central function of a PKI is the provision of digital certificates that can identify an organisation or an individual. It also provides management, storage, distribution and revocation of those digital certificates. A PKI is often referred to as a PKI hierarchy or trust hierarchy. For example, Gatekeeper, the Commonwealth's strategy for PKI use in government (see 5.2) is a hierarchical PKI.

A PKI consists of several components including:

• Certification Authorities (CAs) are trusted by one or more users to create and assign public-key certificates. Optionally the CA may create the users' keys;
• Registration Authorities (RAs) include functions such as an Evidence of Identity check to process requests for new certificates, requests for renewal of certificates and requests for revocation of certificates. In some business models (e.g. Health eSignature Authority) RAs may also generate keys and certificates;
• Certificate or key holders (also subscribers or end users) are issued keys and certificates and can digitally sign and encrypt electronic documents;
• Relying parties receive, validate and accept digital signatures from key holders/subscribers;
• Repositories store and make available certificates and Certificate Revocation Lists (CRLs). CRLs are maintained by CAs and contain all revoked certificates issued by the CA that have not expired.

5.1.1 Employing digital certificates

The opportunity to use digital certificates has been available for a number of years, but generally they have only been implemented for single-use purposes. In these instances, applications have been developed for each user to ensure that the digital certificates can be used for the intended purpose. One of the primary reasons why digital certificates have been implemented using fit-for-purpose designed applications is that most applications employed by Internet users vary greatly in the manner in which they handle digital certificates.

For example: A digital certificate employed from an email platform might not operate in another environment. Service providers may offer a remedial 'patch' or 'plug-in' that will enable digital certificates to work with applications employed by an agency. However, the remedial action employed by one service provider may differ to that of another provider. This could mean that a digital certificate issued by one service provider and employed in an email platform in one agency might not work with the same platform in an agency that employs a different provider's remedial application.

This difficulty in employing digital certificates on a wide-scale is recognised globally. There is growing pressure on application developers to create open standards where digital certificates can be employed and used in the same manner across all Internet applications. In the meantime, 'central validation' or 'trust centre' type facilities, where digital certificates from multiple providers are validated, are warranted. However, this might be a short-term solution if market forces cause application developers to expedite their digital certificate interoperability developments. A rollout of interoperable digital certificates by a major employer of digital certificates might, to a large extent, resolve these difficulties.

In developing a business case for the use of digital certificates, agencies will need to consider the intended deployment, customer base, applications employed by those customers and the solutions offered by service providers.

5.1.2 Business continuity and implementation considerations

n developing a case for PKI, agencies will need to consider some important business continuity issues, particularly where information is encrypted. An agency's ability to continue business might be severely hampered if the information cannot be accessed for some reason.

For example: Agencies need to consider how they will manage their information when it is in an encrypted form and can only be accessed by decrypting it with the agency's private key, which might be held by a staff member who is on leave, sick, overseas, or just cannot be contacted. Agencies also need to consider how they will manage lost or forgotten passwords by personnel needing access to private keys, without which these personnel cannot access the agency's information.

To ensure business continuity, agencies may consider the use of a key recovery service from the agency's Certification Authority, or key escrow by a third party. Agencies may also consider backing up passwords or putting in place an 'unlocking' process for lost or forgotten passwords.

Any implementation of a business continuity process to manage such instances will need to ensure that agency personnel are fully aware and that a complete and reliable audit trail is maintained. The Certification Authority's key recovery service will need to be appropriately evaluated and accredited under the Gatekeeper strategy. If considering backing up passwords, agencies may wish to implement a 'two-person integrity' process where two people from different parts of the agency are involved whenever these business continuity processes are employed.

Agencies should seek legal and security guidance to ensure that these considerations are appropriate. Where the information being protected or signed is the property of the Commonwealth, the Commonwealth is at liberty to use such lawful methods of recovery as are deemed appropriate. The responsibility for Commonwealth policy on this issue rests with the Attorney-General's Department.

The use of products where particular keys are held in escrow or key recovery outside Australia is not permitted under the Gatekeeper strategy.

5.1.3 Recordkeeping implications

Agencies should consider how records subject to authentication and encryption processes will be managed and stored, taking into account privacy and security requirements. For example, access to encrypted information may be compromised when certificates and keys expire while software obsolescence and the degradation of storage mediums may also affect data integrity and accessibility. Agencies should adopt a risk-based approach and consult their records management personnel to develop appropriate management strategies.

For example: Agencies could store unencrypted information in a suitably secure electronic recordkeeping system to ensure continued accessibility and integrity, rather than keep the information in encrypted form in an insecure system. Such information may need to be linked to records that document the authentication and encryption process such as digital certificates, digital signatures, subscriber identity, time and date stamps, revocation checks and message verifications.

The National Archives of Australia is developing recordkeeping guidelines for agencies that use authentication and encryption processes. For further information about this project see the NAA website: http://www.naa.gov.au/recordkeeping

5.1.4 Public Key Technology

Public Key Technology (PKT) is used within PKI to provide users of the technology with the ability to communicate with confidence in an electronic environment. In order to do this they need to know:

• who sent the message (authentication);
• that the message content has not been altered in any way between sending and receiving (integrity);
• that the sender cannot dispute that they created and sent the message (non-repudiation); and
• that only the person the message is directed to can open it (confidentiality).

5.1.5 How PKI works

5.1.6 A typical PKI process flow

While the process may vary somewhat depending on the particular parties involved, the general process flow in a PKI environment is as follows:

• An applicant applies to a CA or RA (depending on the PKI model) for a digital certificate. Alternatively, a Commonwealth agency may commission a CA to offer digital certificates to its clients;
• The CA engages a Registration Authority (RA) to undertake verification of the applicant's identity. This will include verification of a business entity represented by the applicant where appropriate (such as for an ABN-DSC digital certificate);
• The RA advises the CA that identity has been established and that keys and certificates can be issued;
• The CA issues keys and certificates to the applicant (who now becomes a "Subscriber"). This also involves the signing of a Subscriber agreement (i.e. a contract between the CA and the Subscriber) and the issue of the private and public keys, although this may vary according to the CA's business model;
• The Subscriber can then digitally sign an electronic message with their private key to ensure sender authentication, message integrity and non-repudiation and send the message to a relying party;
• The Relying Party receives the message, verifies the digital signature with the Subscriber's (sender's) public key and goes to a repository to check the status/validity of the certificate against a Certificate Revocation List (CRL); and
• The Relying Party then accepts or rejects the certificate depending on the result returned from the CRL and/or their own business judgement.

5.1.7 Is a digital signature the same as a digitised signature?

No. A digitised signature is a computerised image of the written signature of an entity. It may be attached to a word processing document as an image of the original written signature. It can be copied and altered and is not 'bound' to the document.

A digital signature is a cryptographic technique that encrypts a document by applying a mathematical algorithm with a Certificate Holder's private key. This creates a unique identifier which cannot be forged and that can be checked by the receiver to verify authenticity and integrity, thus providing non-repudiation and confirming that the document or file has not been interfered with or altered.

5.1.8 How can we use digital signatures?

Digital signatures can function on electronic documents in the same way as physical signatures do on paper. This means they can be used to automate transactions that are currently carried out on paper. Digital signatures can be applied to email, Internet transactions, World Wide Web pages and more.

Source: Australian Taxation Office
Transactions have traditionally been documented on paper and signing or sealing the paper document has provided an authorisation or intention to bind. Documents are then exchanged to either effect a transaction or provide information. The use of computer systems and the Internet has not changed the basic nature of transactions and information exchange. However, it does provide an alternative method of exchange that offers significant improvements in efficiency and timeliness. The paper document becomes an electronic document and the personal signature or seal becomes a digital certificate.

5.2 Gatekeeper

5.2.1 Background

Gatekeeper is the Commonwealth's strategy for PKI use in government. It was established to assist the development of e-commerce for the exchange of government information and the procurement of services for government. It provides a level of quality assurance through which government can increase confidence in Internet-based transactions. The Gatekeeper Strategy was published in May 1998.

Gatekeeper is the application of policies and practices, particularly in the areas of privacy, security and liability. It is also the application of applicable law such as The Privacy Act (Cth) 1988 and The Electronic Transactions Act (Cth) 1999 and the application of technologies such as PKT and digital certificates.

Gatekeeper has incorporated or adopted national and international standards, existing government policy and guidelines or world's best practice.

Depending upon the risk management decision of users, Gatekeeper provides for the issue of digital certificates capable of protecting information up to and including the Highly Protected classification as described in the Protective Security Manual (PSM, see link under 4.3.2 above). Similarly, transacting parties are free to determine financial limitations in transactions using Gatekeeper digital certificates, based upon risk assessments.

5.2.2 Government requirements

Government policy does not mandate the use of PKI for authenticating online transactions. Use of PKI for authentication purposes is purely a business decision for agencies.

• Commonwealth agencies wishing to use digital certificates to identify their clients and trading partners are required to use Gatekeeper-accredited services and service providers. This has been Government policy since July 1999.
• At the November 2000 Ministerial meeting of the Online Council, States and Territories agreed in principle to the adoption of the Gatekeeper and ABN-DSC strategies, where appropriate, to support electronic transactions within their respective jurisdictions. This means Gatekeeper certificates issued by a State/Territory agency will be accepted by Commonwealth agencies and vice versa.

For more information on the Gatekeeper strategy, visit: http://www.noie.gov.au/projects/publickey/Gatekeeper.htm

5.3 The ABN-DSC

5.3.1 Background

The Australian Business Number - Digital Signature Certificate (ABN-DSC) concept was developed to meet the Government's policy requirement for a broad use digital certificate based around the Australian Business Number (ABN) to simplify business-to-government and business-to-business transactions online. The concept grew out of the tax reform program and the development of the ABN.

It is intended that the ABN-DSC be used primarily for supporting business-to-government online transactions. The Government did not want to burden business with the need to obtain or use a variety of certificates from any number of Commonwealth agencies wanting to undertake online transactions with clients. The ABN-DSC allows businesses to require only one online identity in their dealings with government agencies, thereby reducing both cost and inconvenience to businesses and agencies.

5.3.2 Government requirements

Commonwealth Government decisions in 1999 have required Commonwealth agencies to use the ABN, the Gatekeeper PKI framework and the ABN-DSC.

In July 1999, the Government decided that:

• any future online authentication certificates issued by Commonwealth agencies to business and individuals be Gatekeeper compliant; and
• Commonwealth agencies will use only the ABN as the identifier of business.

In December 1999, the Government decided that the ABN-DSC be issued for whole of Commonwealth Government use to ensure that a single digital signature certificate can be used by a business in electronic transactions with the Commonwealth Government.

At the November 2000 Ministerial meeting of the Online Council, States and Territories agreed in principle to the adoption of the Gatekeeper and ABN-DSC strategies, where appropriate, to support electronic transactions within their respective jurisdictions. This means ABN-DSC certificates issued by a State/Territory agency will be accepted by Commonwealth agencies and vice versa.

For more information, including the ABN-DSC Broad Specification, visit: http://www.noie.gov.au/projects/publickey/abn-dsc.htm

5.3.3 The ABN-DSC and Project Angus

Project Angus is a working group involving the major Australian banks. It aims to establish a framework for e-commerce trust and authentication using the international Identrus%u2122 scheme. Any financial institution operating in Australia that complies with the Identrus terms of eligibility can become a Project Angus member.

In March 2001, the Government announced that Project Angus ABN-DSC conforming digital certificates issued by Project Angus members will be regarded as ABN-DSCs and therefore accepted by Commonwealth agencies.

For more information on Project Angus see: http://www.noie.gov.au/projects/publickey/abn-dsc-angus.htm

For more information on Identrus, visit: http://www.identrus.com/

5.3.4 Business Authentication Framework (BAF)

The BAF is an initiative of the Department of Employment Workplace Relations (DEWR) and the Australian Taxation Office (ATO) in consultation with NOIE.

The BAF will provide a centralised facility that will verify the online identity of business users by securely passing ABN-DSC validation requests between business subscribers, government agencies and ABN-DSC providers. This service will facilitate secure business-to-government e-commerce transactions with government agencies using ABN-DSCs. It will provide one of the key services necessary for secure e-commerce and is scheduled for operation in 2002.