About the Field Level Encryption Implementation

Aptify uses the Cryptographic Services included with Microsoft .NET Framework 2.0 to encrypt and decrypt data files. The AptifySecurityKey assembly implements the Rijndael symmetric encryption algorithm by default, but also supports the Data Encryption Standard (DES) algorithm for backwards compatibility (version 3.5 used a DES implementation).

See http://msdn2.microsoft.com/en-us/library/93bskf9z.aspx for information on the .NET Framework's cryptography model.