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ECB and CTR cryptographically secure pseudorandom number generators

i uh... ECB??? cryptographically secure????

ECB?!?!

Mar 26 at 1:17pmWeb
Show threadgaytabase6d ago

this is my favourite picture in all of cryptography

https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Electronic_codebook_(ECB)

Show thread🌸 lumi-nhac    🌱6d ago
@dysfun oh no! they've encrypted linux! and they demand 1BTC to decrypt linux! ​​
Show threadRoger BW 😷6d ago
@dysfun I expect a competently-written cryptographic library to detect the attempted use of ECB and electrocute the author.
Show threadgaytabase6d ago
@RogerBW a competently written cryptographic library would simply not offer ECB.
Show threadRoger BW 😷6d ago
@dysfun Well, that too, but let's start with what we'd _like_.
Show threadprincess pancake ​6d ago
@[email protected] Hey I'm encrypting white noise
Show threadGraham Sutherland / Polynomial6d ago
@dysfun ECB for a CSPRNG can still be fine, depending on how it's used.
Show threadgaytabase6d ago
@gsuberland i'm scared, graham
Show threadGraham Sutherland / Polynomial6d ago
@dysfun I've used ECB in actual cryptosystems in the last year, even. it's still a useful mode for *very* specific use cases. but you need to know for 100% sure you're not violating a security expectation, otherwise you're fuuuuucked lol
Show threadMarsh Ray6d ago
@gsuberland @dysfun Seems like using ECB in a CSPRNG would require ensuring (@ P < ~2^-128) no duplicate PT blocks?
…which effectively means CTR mode.
Show threadGraham Sutherland / Polynomial6d ago
@marshray @dysfun yeah you basically end up using ECB as a primitive to build a custom mode.
Show threadMarsh Ray6d ago
@gsuberland @dysfun It’s totally justifiable to use “ECB mode” as simply the API to parallelizable block cipher application.
Show threadGraham Sutherland / Polynomial6d ago
@marshray @dysfun hmm. generally you don't want to be doing ECB on anything but a single block per key, but I think we're getting into the weeds a bit.
Show threadMarsh Ray6d ago
@gsuberland @dysfun My point is simply that if we apply a block cipher to a proper sequence of values and XOR the result then that’s CTR mode, even if an API having the letters “ecb” in its name is used.
Show threadGraham Sutherland / Polynomial6d ago
@marshray @dysfun oh, right. I guess? but that's really just AES or whatever as a primitive.