My problem is how to differentiate problems or errors if the
wrong password is supplied or the
password is correct but cyphertext is corrupt or
i am trying to decrypt cleartext or an
intentionally malformed cyphertext designed to reveal password ?
I cant find good examples on stackoverflow or google.
Big thanks for any links to relevant examples on dealing with errors ?
I don’t think you can. After all, as far as I get it, the only way to tell whether you decrypted successfully is by checking the result: if it is well formatted (e.g. starts with a known sequence), you succeeded, otherwise you didn’t.
Say a is the clear text, b the key and c the encrypted data, then
c = a + b
later you take (supposibly) copies of c and b to recompute a copy of a:
a' = c' - b'
If a' != a, the only conclusion you get is that c' isn’t c, b' isn’t b, both, or that - wasn’t the inverse operation of +.