Digital certificate is the document that is stored in a electronic device. Digital certificateestablishes the relationship between user and the public key. Digital Certificate includes thedigital signature. Digital certificate characteristic allows the user to implement key characteristicof the information security? Authentication? Integrity? Privacy? Authorization? NonrepudiationX.509 Certificate maintains a database about a group of users holding it. It binds DistinguishedName which uniquely identifies a certificate entity to user’s public key. Certificate is signed andplaced in directory by CA (Certificate Authority) for retrieval and verification by user associatedkey.The structure of the X.509 certificate is shown below: -VersionCertificate Serial NumberAlgorithm ID? Algorithm ID? ParametersIssuer NameValidity? Not before? Not AfterSubject NameSubject Public Key info? Public key algorithm? Parameters? Subject Public keyIssuer Unique IdentifierSubject Unique IdentifierExtension? Type? Critically? ValueCertificate Signature AlgorithmCertificate SignatureVersionThis field specifies the version number of the certificate. There are 3 versions i.e. version 1,version 2 and version 3.Certificate Serial NumberIt provides a unique integer number to the certificate however the integer number must be apositive integer number.Algorithm IDThis field contains an object identifier (OID) that lay down the algorithm used by CA to sign thecertificate.IssuerThis field contains the Distinguished Name of CA that signed and made the certificate.ValidityThis field lay down the time duration of the certificate i.e. from when to when the certificate isvalid. E.g. The certificate validity date is from 1996, 0ctober 10 to 2017, October 10 this saysthat the certificate is valid during these time period only.Subject NameThis field specifies the distinguished name of the object related with the public key contained inthe certificate.Subject Public Key InfoThis field contains the information about the public key and algorithm associated information.Issuer Unique IdentifierIt contains a unique value which can be used to make X.500 name of CA clear when reused bydifferent entities over time.Subject Unique IdentifierIt contains a unique value which can be used to make X.500 name of CS (Certificate Subject)clear when reused by different entities over time.ImportanceThe importance of X.509 certificate are as follows1) Verifying the person identityX.509 certificate helps to determine who that person is and can make us sure thatthe person really is who they say. X.509 certificates acts at the nationalcitizenship. The government uses the citizenship to verify their people.2) Securing the dataWith the help of x.509 certificate you can secure the data that is intended for youso that other people can’t see it.Asymmetric FunctionIn asymmetric functions, there are two keys. One key is used to encrypt the document whereasanother key is used to decrypt the document. Those keys are called public key and private key.Public key is known to all the people whereas the private key is known only the user.Symmetric FunctionIn symmetric functions, there is only one key i.e. private key which is shared between the twoparties. In this function, the message is encrypted and decrypted by using the same key.Hash FunctionHash function creates a hash value which is also known as message digest. Message digest iscreated by using a mathematical algorithm. The hash value is compared with the receptor hashvalue if both hash value are identical then the user can confirm that there have been no changesin the document. A slight change in the document changes the hash value of the document.