>Craig,
>
>Alex Feldstein recommended me to use your VFPEncryption.FLL for encryption/decryption. I download the zip and read the documentation. It works great! However, I do have one question. When I decrypt it with the wrong key, the function doesn't throw any exception or SetLastError, how do I determine whether a wrong key is entered? In other words, how do I know it decrypted correctly?

The known string that Dragan refers to is often the hash of the password itself. The user then supplies the password, it gets hashed, and then the hash is compared with the stored hash of the password. If the hashes match then the password is ok. The VFP encryption library from Craig includes hashing functions. The hash is not reversible back to the original password.