
The Magic of Math in Modern Cryptography [video] - gcnaccount
https://www.youtube.com/watch?v=mSMQ-xowqAg
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gcnaccount
I prepared this presentation to introduce others to the magical math that
secures our digital lives. It is presented graphically so complex topics can
be appreciated by the expert and layperson alike.

Presentation topics include:

How to achieve privacy when someone is always listening. (encryption)

How to decide on a secret when everyone is watching. (key agreement)

How to turn one random number into unlimited random numbers. (PRNGs)

How to speak in a way that's impossible to imitate. (digital signatures)

How to help protect data without possessing it. (secret sharing)

How to check proofs that you can't see. (zero knowledge proofs)

How to process data you don't have access to. (homomorphic encryption)

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gcnaccount
If anyone would like the slides for this presentation, they are available
here:

[https://docs.google.com/presentation/d/1uXTud6gZaIhJ3aLDuCup...](https://docs.google.com/presentation/d/1uXTud6gZaIhJ3aLDuCupAZyeJYKndbtm1l37Eq1eSMw/edit?usp=sharing)

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captn3m0
I loved the "clock-math" to explain away modulo operations. Gonna send this to
friends interested in crypto, thanks.

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easymovet
I tried out the math for key exchange, 2^y^x=B^x=R=A^y=2^x^y and have a few
questions. If a 3rd person followed the same process and said a number out
loud, say C, then wouldn't they be able to figure out both x and y? (Caveat I
haven't finished the video, just got to slide 12 so far)

wouldn't 2^z^x=B^x=R=C^z=2^x^z and 2^y^z=C^z=R=A^y=2^z^y be true?

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zeroxfe
Key exchange on its own is susceptible to an MITM attack, which is why you use
it along with certs / digital signatures.

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tialaramex
Yes, I suppose such an attack is either what easymovet was proposing or at
least it's the only application.

In a powerful sense what you've got in this case is _two_ secure key
exchanges, Alice to Mallory and Mallory to Bob.

Why this distinction? This is what enables us to use digital signatures to
solve the identity problem in modern protocols. You encrypt the channel
_first_ using this shared secret even though you've no idea who you're talking
to, and only then you may bind proof of your identity to this encrypted
channel and/or look for proof of the other participant's identity.

If Mallory sits between Alice and Bob, there's no use taking the binding of
Bob's identity to the Mallory-Bob channel and showing it to Alice on the
Alice-Mallory channel because it's clearly for the wrong encrypted channel and
Alice will know she isn't really talking (directly) to Bob.

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whatsmyusername
Bigger question. Why is your username green?

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mixedmath
Taking this question at face value --- HN makes "new" accounts green for a few
weeks. This presumably would make a flood of new accounts created to support
some particular opinion or post more obviously manipulative (although I've
never seen that occur here).

~~~
whatsmyusername
Yeah there was no snark involved in the question. It was weird that it was
turbo green.

I forgot this is stack overflow.

