PKI description

Interchange supports public key infrastructure (PKI) to securely trade business documents over the Internet. PKI is a system of components that use digital certificates and public key cryptography to secure transactions and communications.

PKI uses certificates issued by certificate authorities (CAs) to provide authentication, confidentiality, integrity and non-repudiation of data. The following defines these in more detail.

  • Authentication – Authentication is verification of the identity of a person or process. Authentication confirms that a message truly came from the source that sent it.
  • Confidentiality – Confidentiality is the assurance that a message has been disclosed only to the parties authorized to share the information.
  • Integrity – Integrity is the assurance that the information has not been altered in any way and is precisely true to the source.
  • Non-repudiation – Non-repudiation is proof that a recipient received a message. This protects a sender from a false denial that a recipient did not receive a message.

PKI options

There are two PKI options, and Interchange supports both. They are self-signed certificates and commercial PKIs. The option you choose can depend on a number of factors, such as cost, human and system resources, and the degree or sophistication of security desired.

Self-signed certificates generated by Interchange and certificates generated by commercial PKIs all support the X.509 standard for public key certificates. You can use any X.509 certificate, regardless of the source, in document transactions with partners. For example, you can generate a self-signed certificate for your community and export a public encryption key in a certificate with the profile to a partner for use in encrypting and signing documents sent to you. Meanwhile, you can engage in trading with partners who have sent you public keys in Entrust or VeriSign certificates.

The following explains each security option in more detail.

Self-signed certificates

Interchange can generate root certificates in which you are, in effect, acting as your own certificate authority. Interchange supports single-key pair self-signed certificates for both encrypting and signing documents and dual-key pair self-signed certificates in which one certificate is used for encrypting and the other for signing.

Self-signed certificates are easy to make and use. They are best suited for use within relatively small trading groups. This is because you must implicitly trust a partner’s self-signed certificate; there is no chain of trust to independently vouch for the certificate. Such a trust relationship can more suitably be managed among a small number of partners.

Although self-signed certificates can provide a high-degree of security, the degree depends on the vigilance and administrative skills of the persons managing them. Generally speaking, the use of self-signed certificates does not have the rigorous discipline and orderly structure inherent to a commercial PKI.

Commercial PKIs

A commercial PKI is an organization set up for the centralized creation, distribution, tracking and revocation of keys for a potentially large community of partners. A commercial PKI has a documented certificate policy (CP) that indicates the applicability of a public key certificate to a specific community or class of applications with common security requirements. A commercial PKI also has a certification practice statement (CPS), which details the practices the CA follows for issuing public key certificates.

There are two types of commercial PKIs:

  • In house – An in-house PKI enables you to achieve complete control of security policies and procedures, but also carries the burden of management and cost to set up and maintain the system.
  • Outsourced – You can leverage the services of PKI systems such as VeriSign, Entrust and other third-party certificate authorities. You purchase keys and certificates for use in trading partner relationships and let the CA manage security policies and such details as certificate revocation. The level of outsourcing can range from purchasing an end-entity public key certificate of a certain validity period from a commercial PKI to outsourcing all of the PKI services that your organization requires.

The role of trust in PKI

PKI establishes digital identities that can be trusted. The CA is the party in a PKI responsible for certifying identities. More than generating a certificate, this entails verifying the identity of a subscriber according to established policies and procedures. This is the case for in-house and outsourced PKIs. In an organization that generates and uses its own self-signed certificates, the trading parties must verify the certificates and establish a direct trust. Once established that an identity or issuer of an identity can be trusted, the trust anchor’s certificate is stored in a local trust list.

Interchange has a local trust list for storing and managing established trust relationships ( Add a certificate). The application maintains a list of common public CA certificates similar to those kept in web browsers. Although convenient, this pre-determination of trust might not complement your organization’s security policy. The decision of who to trust rests with your organization. For example, a trader might accept certificates issued by its own root CA and its trading partners’ root CA, but not from partner B, who the trader has not done business with in the past. If you choose not to accept partner B’s root CA certificate, your system does not accept any certificates issued by partner B. The greater the number of root CA certificates you choose to accept, the more open your community is to others.


The use of self-signed certificates relies on users to exchange certificates and establish trust in each other. This informal web of trust works for small groups, but can become unmanageable for large numbers of partners. In contrast, an in-house or outsourced PKI uses hierarchies, where a certificate authority serves as a trust anchor for many users. Once trust has been established for the certificate authority, it is unnecessary to re-establish the trust for other certificates the CA issues. Establishing hierarchies of users scales equally well for small and large groups.

Certificate revocation

A certificate is expected to be usable for its entire validity period. However, there are circumstances when a certificate should no longer be considered valid even though it has not expired. Possible circumstances range from a user name change to suspected compromise of the private key. In such circumstances an in-house or outsourced CA can revoke the certificate. Interchange can be configured to compare your partners’ certificates against lists of revoked certificates issued by CAs. However, self-signed certificates cannot be revoked. You must notify all partners using the certificate that it should no longer be trusted.

Dual-key pairs

Support for two pairs of public-private keys is a fundamental requirement for some PKIs (for example, Entrust). One key pair is for data encryption and the other key pair is for digitally signing documents. Encryption key pairs and signing key pairs are a result of conflicting requirements. One such requirement is to support different algorithms for encryption and digital signature pairs and different validity periods. Another reason is to support data recovery, which requires the private keys for decrypting to be securely backed up, but non-repudiation, which requires the private keys for signing, not to be backed up. There also might be the requirement to support updating encryption key pairs and managing decryption key histories even though this conflicts with the requirement to securely destroy the private key used for signing when updating signing key pairs. Using two key pairs — an encryption key pair and signing key pair — solves these conflicting requirements.

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