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X.509
EntityQ1065865· pop 30· linked from 212 articles

Also known as PKIX

In cryptography, X.509 is an International Telecommunication Union (ITU) standard defining the format of public key certificates. X.509 certificates are used in many Internet protocols, including TLS/SSL, which is the basis for HTTPS, the secure protocol for browsing the web. They are also used in offline applications, like electronic signatures.

Key facts

Technology standard.title
X.509
Technology standard.long_name
Information technology - Open Systems Interconnection - The Directory: Public-key and attribute certificate frameworks
Technology standard.status
In force (Recommendation)
Technology standard.version
9.2
Technology standard.organization
ITU-T
Technology standard.committee
ITU-T Study Group 17
Technology standard.base_standards
ASN.1
Technology standard.related_standards
ISO/IEC 9594-8:2020, X.500
Technology standard.domain
Cryptography
Technology standard.series
X
Technology standard.first_published
1.0 at
File format.name
X.509 certificate
File format.mime
application/pkix-cert
File format.uniform type
public.x509-certificate

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~38 min read

Article

26 sections
Contents
  • History and usage
  • Certificates
  • Structure of a certificate
  • Extensions informing a specific usage of a certificate
  • Extended Validation certificates
  • Certificate filename extensions
  • Certificate chains and cross-certification
  • Examples
  • Example 1: Cross-certification at root Certification Authority (CA) level between two PKIs
  • Example 2: CA certificate renewal
  • Sample X.509 certificates
  • End-entity certificate
  • Intermediate certificate
  • Root certificate
  • Security
  • Architectural weaknesses
  • Problems with certification authorities
  • Implementation issues
  • Cryptographic weaknesses
  • Mitigations for cryptographic weaknesses
  • PKI standards for X.509
  • PKIX Working Group
  • Major protocols and standards using X.509 certificates
  • See also
  • References
  • External links

In cryptography, X.509 is an International Telecommunication Union (ITU) standard defining the format of public key certificates. X.509 certificates are used in many Internet protocols, including TLS/SSL, which is the basis for HTTPS, the secure protocol for browsing the web. They are also used in offline applications, like electronic signatures.

An X.509 certificate binds an identity to a public key using a digital signature. A certificate contains an identity (a hostname, or an organization, or an individual) and a public key (RSA, DSA, ECDSA, ed25519, etc.), and is either signed by a certificate authority or is self-signed. When a certificate is signed by a trusted certificate authority, or validated by other means, someone holding that certificate can use the public key it contains to establish secure communications with another party, or validate documents digitally signed by the corresponding private key.

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