Yah, I stored some personal files on NSA's network, could you retrieve them for me? Thanks!
Seriously though, if these really are *your* files, you'll need to know the cipher used. In order to encrypt something, a cipher is used (the algorithm used to actually encode the data, it becomes ciphertext), you'll need to know which one. DES, 3DES, RC4, Twofish, AES, ad nauseum...
[edit]Oh, and note, just because you know the cipher doesn't necessarily mean you'll be able to decipher them. That is, of course, unless you have discovered immortality and infinite processing power.[/edit]