write short note on X.509  in CSS

X.509 is a digital certificate that is built on top of a widely trusted standard known as ITU or International Telecommunication Union X.509 standard, in which the format of PKI certificates is defined. X.509 digital certificate is a certificate-based authentication security framework that can be used for providing secure transaction processing and private information. These are primarily used for handling the security and identity in computer networking and internet-based communications.

 Generally, the certificate includes the elements given below:

• Version number: It defines the X.509 version that concerns the certificate.
• Serial number: It is the unique number that the certified authority issues.
• Signature Algorithm Identifier: This is the algorithm that is used for signing the certificate.
• Issuer name: Tells about the X.500 name of the certified authority which signed and created the certificate.
• Period of Validity: It defines the period for which the certificate is valid.
• Subject Name: Tells about the name of the user to whom this certificate has been issued.
• Subject’s public key information:  It defines the subject’s public key along with an identifier of the algorithm for which this key is supposed to be used.
• Extension block: This field contains additional standard information.
• Signature: This field contains the hash code of all other fields which is encrypted by the certified authority private key. Applications of X.509 Authentication Service Certificate:Many protocols depend on X.509 and it has many applications, some of them are given below:
  • Document signing and Digital signature
  • Web server security with the help of Transport Layer Security (TLS)/Secure Sockets Layer (SSL)  certificates
  • Email certificates
  • Code signing
  • Secure Shell Protocol (SSH) keys
  • Digital Identities