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RFC 5280 - Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile

Publication Date: May 2008
Status: Standards Track Protocol
Authors: D. Cooper (NIST), S. Santesson (Microsoft), S. Farrell (Trinity College Dublin), S. Boeyen (Entrust), R. Housley (Vigil Security), W. Polk (NIST)
Obsoletes: RFC 3280, RFC 4325, RFC 4630

Abstract​

This memo profiles the X.509 v3 certificate and X.509 v2 certificate revocation list (CRL) for use in the Internet. An overview of this approach and model is provided as an introduction. The X.509 v3 certificate format is described in detail, with additional information regarding the format and semantics of Internet name forms. Standard certificate extensions are described and two Internet-specific extensions are defined. A set of required certificate extensions is specified. The X.509 v2 CRL format is described in detail along with standard and Internet-specific extensions. An algorithm for X.509 certification path validation is described. An ASN.1 module and examples are provided in the appendices.

Table of Contents​

Main Sections​

Appendices​

Key Concepts Overview​

What is an X.509 Certificate?​

An X.509 certificate is a digital document used to prove identity and establish secure communications on the Internet. It forms the foundation of technologies like HTTPS, TLS/SSL, code signing, and email encryption.

Core Functions:

  • Identity Verification: Proves "who you are"
  • Public Key Distribution: Securely distributes public keys
  • Trust Chain: Establishes trust through Certificate Authorities (CAs)

Basic Certificate Structure​

Certificate ::= SEQUENCE {
   tbsCertificate       TBSCertificate,
   signatureAlgorithm   AlgorithmIdentifier,
   signatureValue       BIT STRING
}

Key Fields:

  • Version: Certificate version (v1, v2, v3)
  • Serial Number: Unique identifier assigned by CA
  • Signature Algorithm: Algorithm used to sign the certificate
  • Issuer: DN of the entity that signed the certificate
  • Validity: Time period during which the certificate is valid
  • Subject: DN of the entity associated with the public key
  • Subject Public Key Info: Public key and algorithm identifier
  • Extensions: Additional information (v3 only)
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