A method of identification similar to a driver’s license for the Internet. Certificates are also used for cryptography. This method differs from many others in that it is generally much more transparrent to the end-user and is almost always commercial in nature. This money spent pays for Certificate Authorites (CA), sometimes known as public key infrastructures (PKI), to track the use of a certificate and work as an automatic service that affirms the validity of a communication.
Certificates can utilize both Public-Key Cryptosystems for encryption and Hashes for authentication. Certificates are used in almost all Web transations (SSL) and much of the Web’s e-mail using S/MIME.
PGP and GPG-encrypted email varies from certificate-based systems in that the user is the sole owner of any key pairs generated and it is their responsibility to check for validity using fingerprints or Key servers. Technically, there is no difference between a certificate and a PGP/GPG key pair only in the responsibilty for how they are handled.
S/MIME and SSL are generally much easier than PGP/GPG but don’t serve the very paranoid and aren’t free.
Some certificate providers:
TakeDown.NET -> “Certificate”