Certification path validation algorithm

Certification path validation algorithm

The certification path validation algorithm is the algorithm which verifies that a given certificate path is valid under a given public key infrastructure (PKI). A path starts with the Subject certificate and proceeds through a number of intermediate certificates up to a trusted root certificate, typically issued by a trusted Certification Authority (CA).

Path validation is necessary for a relying party to make an informed trust decision when presented with any certificate that is not already explicitly trusted. For example, in a hierarchical PKI, a certificate chain starting with a web server certificate might lead to a small CA, then to an intermediate CA, then to a large CA whose trust anchor is present in the relying party's web browser. In a bridged PKI, a certificate chain starting with a user at Company A might lead to Company A's CA certificate, then to a bridge CA, then to company B's CA certificate, then to company B's trust anchor, which a relying party at company B could trust.

RFC 3280 [1] defines a standardized path validation algorithm for X.509 certificates, given a certificate path. (Path discovery, the actual construction of a path, is not covered.) The algorithm takes the following inputs:

  • The certificate path to be evaluated;
  • The current date/time;
  • The list of Certificate Policy OIDs acceptable to the relying party (or any);
  • The trust anchor of the certificate path; and
  • Indicators whether policy mapping is allowed and how/when/whether the "any" policy OID is to be tolerated.

In the standardized algorithm, the following steps are performed for each certificate in the path, starting from the trust anchor. If any check fails on any certificate, the algorithm terminates and path validation fails. (This is an explanatory summary of the scope of the algorithm, not a rigorous reproduction of the detailed steps.)

  • The public key algorithm and parameters are checked;
  • The current date/time is checked against the validity period of the certificate;
  • The revocation status is checked, whether by CRL, OCSP, or some other mechanism, to ensure the certificate is not revoked;
  • The issuer name is checked to ensure that it equals the subject name of the previous certificate in the path;
  • Name constraints are checked, to make sure the subject name is within the permitted subtrees list of all previous CA certificates and not within the excluded subtrees list of any previous CA certificate;
  • The asserted Certificate Policy OIDs are checked against the permissible OIDs as of the previous certificate, including any policy mapping equivalencies asserted by the previous certificate;
  • Policy constraints and basic constraints are checked, to ensure that any explicit policy requirements are not violated and that the certificate is a CA certificate, respectively. This step is crucial in preventing some man in the middle attacks [2];
  • The path length is checked to ensure that it does not exceed any maximum path length asserted in this or a previous certificate;
  • The key usage extension is checked to ensure that is allowed to sign certificates; and
  • Any other critical extensions are recognized and processed.

If this procedure reaches the last certificate in the chain, with no name constraint or policy violations or any other error condition, then the certificate path validation algorithm terminates successfully.

External references

  1. ^ RFC 3280 (2002), chapter 6., a standardized path validation algorithm for X.509 certificates.
  2. ^ Moxie Marlinspike, New Tricks For Defeating SSL In Practice, Black Hat DC Briefings 2009 conference.


See also

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Extended Validation Certificate — Extended Validation Certificates (EV) [ The term validation as used here should not be confused with the Certification path validation algorithm commonly found in a certificate context.] are a special type of X.509 certificate which require more… …   Wikipedia

  • X.509 — In cryptography, X.509 is an ITU T standard for a public key infrastructure (PKI) for single sign on and Privilege Management Infrastructure (PMI). X.509 specifies, amongst other things, standard formats for public key certificates, certificate… …   Wikipedia

  • Public key infrastructure — In cryptography, a public key infrastructure (PKI) is an arrangement that binds public keys with respective user identities by means of a certificate authority (CA). The user identity must be unique for each CA. The binding is established through …   Wikipedia

  • SCVP — The Server based Certificate Validation Protocol (SCVP) is an Internet protocol for determining the path between a X.509 digital certificate and a trusted root (Delegated Path Discovery) and the validation of that path (Delegated Path Validation) …   Wikipedia

  • Public key certificate — Diagram of an example usage of digital certificate In cryptography, a public key certificate (also known as a digital certificate or identity certificate) is an electronic document which uses a digital signature to bind a public key with an… …   Wikipedia

  • XML — Infobox file format name = Extensible Markup Language icon = logo = extension = .xml mime = application/xml, text/xml (deprecated) type code = uniform type = public.xml magic = owner = World Wide Web Consortium genre = Markup language container… …   Wikipedia

  • List of computing and IT abbreviations — This is a list of computing and IT acronyms and abbreviations. Contents: 0–9 A B C D E F G H I J K L M N O P Q R S T U V W X Y …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”