An X.509 certificate is a digital certificate that allows verifying a user’s identity so we can be sure of whothat person really is. X.509 allows the person with it to decrypt and read the data which has beenencrypted and sent to them. It uses internationally accepted X.509 public key infrastructure standard toverify whether a public key belongs to user, computer or service identity contained with an authorizedcertificate. In simple words this certificate helps to identify the user as well as where the user orcomputer got this certificate from. X.509 certificates are also mentioned as Secured Socket Layer (SSL).Basically the X.509 certificate allows a user to be safe on the internet from unwanted parties anduntrusted parties. The structure of X.509 certificate is as follows and includes the following things:1) Version: version basically means the different form of same software or in this case the X.509certificate. This field shows which version the certificate is and whether it is now or previouslyexisting.2) Algorithm information: algorithm means step by step instruction about how to obtain a solution.But in this case the algorithm information shows the algorithm which is used by the issuer tosign and verify the certificate.3) Validity period of the certificate: validity of the certificate basically shows from when thecertificate is issued ; started and till when the certificate is useful or its expiration date.4) Serial number: serial number allows the x.509 certificate to be unique. Unique in a sense that ithelps the certificate to be separated from other issued certificate.5) Issuer name: this includes the unique name of the trusted certificate authority that has issuedthe certificate to the user or computer.6) Subject name: this includes the unique name of the user that has been issued the certificate to.7) Public key information of the subject: it provides the information about the public key that hasbeen assigned to the distinguished subject (user).Since X.509 certificate is the standard for digital certificate, its importance is that it is the basisof the Internet’s public key infrastructure standard. It also helps to verify authenticity of a userand its brand. These certificates are also portable in nature meaning that it can be freelydistributed by trusted authorities. X.509 certificate also helps in securing data while transmittingit over a network form hackers. An example of X.509 certificate can be taken in the followingmanner. Since we know that the X.509 certificate is used to verify a person’s identity, you canassume that X.509 certificate is like a boarding pass of an airline. The boarding pass of an airlineconsists of your name, flight number, unique seat id, unique boarding pass number and date aswell as time. This boarding pass allows you to enter an airplane by verifying you at the boardinggate and allows you access to the plane and finally your seat. If you lose it or damage it in anyway you are not allowed access to the airplane and you will have to make a new boarding pass.So, you keep your boarding pass safe with you to get access to you airplane in order to get toyour destination. X.509 certificate also works in a similar way.Symmetric key cryptography in X.509 certificate:In this type of encryption a single key is used to encrypt and decrypt data. It is also known assecret key encryption because the two users who are engaged in transferring and receiving ofdata both have a secret shared key. This secret key is used to encrypt the data from the senderuser and decrypt the data from the receiving user. This type of encryption is relatively faster andis less complex. It is used in authentication in X.509 certificates. Here the secret key frequentlychanges and can be made according to one’s desire. Disadvantage of this is that it often securesystem failure due to a break in the key distribution technique.Asymmetric key cryptography in X.509 certificate:In asymmetric key cryptography a certain key is used to seal the data and an entirely differentkey is used to unlock the data. It is also known as public key private key cryptography becausethe public key is made available to the world and any one can use it but the private key is onlyavailable for the user receiving the message. Here if a user locks the data with a public key anyother person with a public key cannot decipher the data and read it but only the person with theprivate key can read the data. Since X.509 certificate consists of information such as yourinformation and your public key, users can take your public key and send you classified data andonly you can decipher it safely for your use.Hash functions in X.509 certificate:Hashing is a technique which is different than encryption. It is different than encryption in such away that in encryption it requies two steps for the process to complete; one to encrypt andanother to decrypt. But in hashing it converts a message into a fixed length of value that isirreversible. Some techniques of hashing are MD5 and SHA-1. The real data cannot be retrievedfrom hashing because hashing is only used to verify a data. Hash is basically the result of the realdata and a secret key and is commonly used for error checking.