obfsproxy should use C implementation of UniformDH

[asn]

We are currently using a C implementation of UniformDH that is quite slow (even with gmpy2 for mod exp).

Yawning implemented UniformDH in C using OpenSSL and we should use his library.

He posted an obfsproxy patch in #11015 :
https://trac.torproject.org/projects/tor/attachment/ticket/11015/0001-Add-support-for-using-py-uniformdh.patch

And the implementation can be found in:
​https://github.com/Yawning/py-uniformdh

[yawning]

Just to clarify this a bit, the gmpy (gmpy2) implementations are about as fast as the OpenSSL code I have (with a slight advantage to the gmpy code for key generation because I *always* generate 2 public keys to avoid exposing which one is chosen), but the OpenSSL code I have applies blinding. I could get a faster implementation but the main gain is that it's more resistant to timing attacks.

If using OpenSSL is acceptable, then #11050 should be solved as well (either by switching from PyCrypto to M2crypto, or perhaps by extending the module I wrote to cover all of the cryptography required for obfsproxy). The latter approach would also allow better management of key material since the shared secret/session keys don't ever need to be seen by the actual python code, so I think it may be better from a paranoia stand point, but the downside is that someone would need to write the code.

I do note that ensuring data integrity/secrecy once the transport is known (at the point people are exploiting these problems) is outside of the obfs3 threat model, but it still feels sloppy to me.

[teor]

Set all open tickets without a severity to "Normal"

[teor]

asn does not need to own any obfuscation tickets any more. Default owners are trouble.

[cohosh]

tickets are unassigned, reverting to 'new'