You'd need to check that the right key was used. If a way to tell whether the correct key was used was added to the library this would decrease the overall security of the library by making it succeptible to brute force attacks among other things (the library would have to embed the key in the ciphertext so it could check it and this would not be a good thing). If you don't know what the right key should be or what the resultant plaintext should be when decrypting the ciphertext then there is no way to know whether the key used is the right one.

Perhaps you could explain a little more about what you are trying to do and why not having the ability to know whether the correct key was used is causing you a problem (or why you feel that such a feature would be useful to you)?

>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?