"You will never discover this corruption after the fact by any statistical method (guesswork)."

yes sir, i competently understand that, and realise there is no way to actually tell if a encrypted file is corrupted in anyway, but you can measure certain things to help signify (to a certain extent) if the file is corrupted or partially corrupted. otherwise you would need the means to decrypt the file and checksum it like said earlier, which will not work because the file cannot be decrypted because the keys are not known and more than likely will never be known. so i am just trying to come up with some methods to check it for any possibility of being corrupt.

the program i used a long time ago computed this std dev from any given file. and from each revision of this file, the std dev was always within a marginal range of the expected outcome. if it was WAY off, then you know the file was probably corrupted.

that along with calculating entropy + byte for byte repetition checking + the percentage of how many times each byte character is in said file will go along way i think :)

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