As far as I know, CBC mode, even with a null IV, will encrypt identical plaintext blocks to unique ciphertext blocks within a single file. The purpose of an IV is to obscure the similarities between multiple ciphertexts, not to obscure the similarities within a single ciphertext. So, would it be just as effective to use a null IV as it would be to use a random IV when encrypting a single file? As far as I see it, it's just one less value to store.
I took a look at  but my question is not the same.  I have unique keys encrypting each plaintext (in CBC mode, AES-256) and I do not use a key to encrypt more than one plaintext. Is it insecure to use null IVs in this case? If it is insecure, why?
Puzzle: Find largest rectangle (maximal rectangle problem) Short story: people rediscover how to do math and want to put people in bombs Many years ago I remember reading a short story about an advanced civilization at war that rediscovers how to do math mentally. The reason I remember it is the guy tells it to government officials who are delighted because it means they can put people inside bombs or missiles instead of computers, which were thought to be more valuable.  I believe this is one of those stories I read in a science fiction anthology my father brought home on one of his business trips in the sixties or seventies. Is there any way to keep a command from being added to your history? I have a command that I want to keep out of my history file, and I really don't care to have it there when I search the history stored in memory, though that's less of a concern. 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