You can easily en-/decrypt files with a size limit of 100MB.
This tool have also a contact list implemented, so you can store the public keys of your friends.
XTEA (eXtended Tiny Encryption Algorithm) support for db4o open source object database. XTEA is a block cipher that operates on a 64-bit block size with a 128-bit key. An extremely tiny but very fast encryption algorithm (with cycles less than 32 rounds)