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curve25519-donna: Curve25519 elliptic curve, public key function

http://code.google.com/p/curve25519-donna/

Adam Langley <agl@imperialviolet.org>

Derived from public domain C code by Daniel J. Bernstein <djb@cr.yp.to>

More information about curve25519 can be found here
  http://cr.yp.to/ecdh.html

djb's sample implementation of curve25519 is written in a special assembly
language called qhasm and uses the floating point registers.

This is, almost, a clean room reimplementation from the curve25519 paper. It
uses many of the tricks described therein. Only the crecip function is taken
from the sample implementation.
