A certificate is basically a key that can be used to sign or encrypt documents and that has some further information attached to it, like who it belongs to or how long it will be valid and so on. What makes it a certificate is the fact that some authority certifies that this key is authentic and belongs to you. This is the public part of a key-pair used in a public-key infrastructure. In order to get a working certificate you need to do the following:

1. generate a key-pair
   • the public key, which becomes the certificate
   • the secret key, which you always must keep for yourself
2. have some certification authority approve your certificate
3. publish your certificate to
   • allow other users to verify signatures that you created using your secret key
   • allow other users to decrypt documents that you encrypted using your secret key
   • allow other users to encrypt documents that only you can decrypt using your secret key