posted 14 years ago
How did you "decrypt"? There is an endless variety of ciphers, you can't possibly try them all, particularly not if you don't have the keys. And even if you tried just one, and got no exception, how would you decide that the result is not encrypted further? It might be a binary file in cleartext in a format you don't know, or it might be an encrypted file. So, there is no way to know for sure unless you have more information about the file that you didn't mention.