Quick summary of the main purpose here:  X.509 certs are used in publickey infrastructure for protocols such as SSL and SET.  These certificatesinvolve ISO/CCITT standard technologies such as ASN.1/DER, which controlthe format of the data being transmitted.  X.509 itself describes thecontent of the data (e.g. X.500 user name, public key for that user, more)and how to sign it. +++	+++	+++	+++	+++	+++	+++	+++	+++ The X.509 support in JDK 1.2 builds on the java.security signature andkey management APIs.  The following packages provide the X.509 support:     sun.security.util ... holds DER utilities, for parsing and generating	streams of DER-encoded data values, including object identifiers.     sun.security.x509 ... basic X.509 certificate parsing and generation	framework, including X.509 keys, X.500 names, algorithm IDs,        X.509 v3 extensions, and more. +++	+++	+++	+++	+++	+++	+++	+++	+++ Information which may be useful when you work with X.509 certificates isfound in:     The IETF has a public key infrastructure working group, PKIX.    See http://www.ietf.org for more information.     RFC 1422, which describes the key management infrastructure for    the Privacy Enhanced Mail (PEM) system.  It builds on X.509,    and is perhaps the most useful overview I've found.     RFC 1777, which describes the Lightweight Directory Access    Protocol (LDAP) that many organizations are expecting will help    address online certificate distribution over the Internet.     RFC 3280, which describes the Internet X.509 Public Key    Infrastructure Certificate and CRL Profile.       RSA DSI has a bunch of "Public Key Cryptography Standards" (PKCS) which    have been relatively well accepted.  They build on top of the X.509    infrastructure.  You can FTP them from ftp://ftp.rsa.com/pub/pkcs, in    either PostScript or ASCII format.     RSA DSI has also provided a "Layman's Guide" to ASN.1/DER, with    examples from the X.509 and PKCS standards.  This is available from    the PKCS FTP area noted above.