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Security Fundamentals & Crypto · Intermediate

X.509

ITU-T standard defining the format of public key certificates and certificate revocation lists.

Definition

X.509 v3 certificates include fields such as version, serial number, signature algorithm, issuer, validity, subject, subject public key info, and extensions like Subject Alternative Name, Key Usage, Extended Key Usage, and Basic Constraints. The Internet profile is defined in RFC 5280. X.509 is the basis for TLS, S/MIME, and most enterprise PKI.

Example

A TLS server certificate's Extended Key Usage contains 'TLS Web Server Authentication'.

Exam tip

Know the major fields; the CA's digital signature on the certificate is what makes it trustworthy.

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