The basic X.509 format was defined by ISO/IEC and ANSI X9 and is described below in ASN.1:

 Certificate  ::=  SEQUENCE  {
     tbsCertificate       TBSCertificate,
     signatureAlgorithm   AlgorithmIdentifier,
     signature            BIT STRING  }
 

These certificates are widely used to support authentication and other functionality in Internet security systems. Common applications include Privacy Enhanced Mail (PEM), Transport Layer Security (SSL), code signing for trusted software distribution, and Secure Electronic Transactions (SET).

These certificates are managed and vouched for by Certificate Authorities (CAs). CAs are services which create certificates by placing data in the X.509 standard format and then digitally signing that data. CAs act as trusted third parties, making introductions between principals who have no direct knowledge of each other. CA certificates are either signed by themselves, or by some other CA such as a "root" CA.

The ASN.1 definition of tbsCertificate is:

 TBSCertificate  ::=  SEQUENCE  {
     version         [0]  EXPLICIT Version DEFAULT v1,
     serialNumber         CertificateSerialNumber,
     signature            AlgorithmIdentifier,
     issuer               Name,
     validity             Validity,
     subject              Name,
     subjectPublicKeyInfo SubjectPublicKeyInfo,
     }
 

Here is sample code to instantiate an X.509 certificate:

 InputStream inStream = new FileInputStream("fileName-of-cert");
 X509Certificate cert = X509Certificate.getInstance(inStream);
 inStream.close();
 

 byte[] certData = <certificate read from a file, say>
 X509Certificate cert = X509Certificate.getInstance(certData);
 

In either case, the code that instantiates an X.509 certificate consults the value of the cert.provider.x509v1 security property to locate the actual implementation or instantiates a default implementation.

The cert.provider.x509v1 property is set to a default implementation for X.509 such as:

 cert.provider.x509v1=com.sun.security.cert.internal.x509.X509V1CertImpl
 

The value of this cert.provider.x509v1 property has to be changed to instantiate another implementation. If this security property is not set, a default implementation will be used. Currently, due to possible security restrictions on access to Security properties, this value is looked up and cached at class initialization time and will fallback on a default implementation if the Security property is not accessible.

Note: The classes in the package javax.security.cert exist for compatibility with earlier versions of the Java Secure Sockets Extension (JSSE). New applications should instead use the standard Java SE certificate classes located in java.security.cert.