

Ask HN: How can i verify perfect secrecy of a cryptosystem? - sgy

i&#x27;m playing with an encryption algorithm (demo: https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=h1kABn5dfXc). how can i prove it&#x27;s information-theoretically secure?
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bmm6o
Your key is too short - it's not possible for it to be information-
theoretically secure. That's just one of its obvious faults: it looks like it
doesn't even work all of the time, the system generates a key instead of
taking on as input, the data undergoes unnecessary expansion, etc etc etc.

~~~
sgy
\- the first time, i intentionally modified the key [to show that it doesn't
work just on any number input]

\- the system can be updated to take a key as input.

\- right, it expands by nearly a half; that's used to make it just as secure
as the one-time pad, but more practical. [and this is what i want to verify,
then optimize].

if you have the time, i'd love to hear more feedback. thank you very much.

~~~
bmm6o
> that's used to make it just as secure as the one-time pad, but more
> practical.

No. There is no such thing as "just as secure as the one-time pad but more
practical". If you want information-theoretic security you have to pay for it,
and if you don't pay for it you don't get it. Like, there are theorems. That's
why mention of OTP is a good proxy for not understanding modern cryptography.
Everyone who's serious about it knows that not only are the benefits of the
OTP not achievable in almost every practical situation (due to key
distribution), nobody actually needs that level of security when 256-bit
algorithms are available.

~~~
sgy
you're correct.

my claim is a bit different though; it's a new take on encrypting text that
has no properties of existing crypto systems. used OTP as an analogy. i think
it's a fallacy to do so.

