X.509 Certificates

Simple Definition for Beginners:

X.509 certificates are digital documents used in internet security to verify the identity of websites, servers, or individuals. They contain information such as the owner’s identity, public key, and digital signature, ensuring secure communication and authentication online.

Common Use Example:

When you visit a secure website (HTTPS), your browser checks the X.509 certificate presented by the site to verify its authenticity and establish a secure connection for transmitting sensitive data like login credentials.

Technical Definition for Professionals:

X.509 certificates are part of the Public Key Infrastructure (PKI) and adhere to the X.509 standard defined by the International Telecommunication Union (ITU). Key aspects of X.509 certificates include:

• Certificate Authority (CA): Issued by a trusted CA, X.509 certificates validate the ownership of public keys and bind them to specific entities (e.g., websites, servers, individuals).
• Public Key Cryptography: X.509 certificates use asymmetric encryption to securely transmit public keys, allowing for secure communication and digital signatures.
• Certificate Fields: Information in X.509 certificates includes the subject (entity), issuer (CA), validity period, public key, digital signature, and certificate extensions (e.g., key usage, subject alternative name).
• Certificate Revocation: X.509 certificates can be revoked if compromised or no longer valid, with mechanisms like Certificate Revocation Lists (CRLs) or Online Certificate Status Protocol (OCSP).
• Certificate Chains: In complex PKI setups, X.509 certificates can form chains where intermediate certificates verify the authenticity of end-entity certificates.