Write your own decryption software, see if that software can undo the encryption. For this to fail one of the following must hold: 1 you made a mistake in your

Write your own decryption software, see if that software can undo the encryption. For this to fail one of the following must hold: 1 you made a mistake in your decryption that matches a mistake in the encryption. 2 The encryption scheme allows incorrect cyphertext to decrypt to correct plaintext 3 The encryption software writes more than the supposed cyphertext. 1 requires a mistake on your end, so is hard for malicious entities to abuse. 2 is a feature of the cypher, as such can be defended against in design. 3 can be defended against by observing the encryption software (look for all disk modification and network activity).