
Dining Cryptographers Problem - yasp
https://en.wikipedia.org/wiki/Dining_cryptographers_problem
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tearex
Nice puzzle but the problem seems to be reduced to a problem of safely
distributing keys, in this case behind the menu (what if I'm in another
country?). Also, it's similar to one-time pad [1] where you generate a random
key with same length as the message and XOR them. This achieves perfect
secrecy with the question on how you distribute keys.

[1] [https://en.wikipedia.org/wiki/One-
time_pad](https://en.wikipedia.org/wiki/One-time_pad)

~~~
nullc
> but the problem seems to be reduced to a problem of safely distributing
> keys,

That's just a standard problem for asymmetric cryptography.

Each person at the table announces a public key. Each party can now derive a
shared secret with each other party using diffie-hellman. The shared secret
can be used to produce a pseudorandom stream using a CSPRNG or stream cipher.

~~~
tearex
Yes, and this is now a question if you can trust that the other person is not
the adversary so we introduce trusted third parties and certificates.

~~~
nullc
One doesn't need to use trusted third parties to use public keys.

In fact, the most popular existing TTP public key infrastructure provides
extremely limited security (someone who can intercept http near an IP where
your domain name resolves can easily obtain an SSL cert with your domain name
on it).

~~~
stonedartist
>someone who can intercept http near an IP where your domain name resolves can
easily obtain an SSL cert with your domain name on it

Sorry to hijack this thread, can you please give me a keyword or link as to
what this type of attack is called?

I have plans to host a domain, so wanted to know what this threat is called.
Thanks!

~~~
nullc
I'm not sure what you'd call it other than man-in-the-middle.

The issue is that CA's (for various defensible reasons-- including that there
isn't much better possible within their framework, it's not like they know you
personally...) will issue a cert for your domain to any party that can throw a
file up on it that their automation fetches via http.

In practice this means a MITM near your server (or, technically, anywhere
between any CA that will issue certs for your domain and your server), or
between your CA and the DNS results can get certs for your name and there
isn't much you can do about it.

------
motohagiography
Naively, this seems analogous to differential privacy, where the distribution
of the result is the same as the real one, without revealing the individual
elements - or is the dining cryptographers a full proof? I couldn't quite tell
on first read.

~~~
nullc
I think your question is a little too vague.

In general case DCnets provide perfect sender privacy (among participants, of
course). If there are multiple messages their senders will be completely
unlinkable.

Specific implementations might use schemes for collision resolution that break
privacy, though there is no requirement that collisions (absent malicious
participants) even be possible at all-- with fancy enough technology applied.

