The above is really a discussion of symmetric encryption (first part of above) and asymmetric encryption (the latter part). While AES may be considered the best symmetric algorithm for symmetric encryption, there are other good ones that can be used, so that info is not complete. The asymmetric discussion above is also not fully correct. With asymmetric encryption used in PGP, the data is actually symmetrically encrypted (PGP defaults to using AES). It is then the randomly generated AES symmetric key used for the data encryption that is encrypted to a public key of the recipient. The recipient uses his/her private key to decrypt the AES key, and the AES key is then used to decrypt the data. So, in either case, symmetric encryption is used (because it is so much faster than asymmetric encryption. And the public key encryption is used as a secure way of transmitting the symmetric (in this case, AES) key.