Related slides from Peter Schwabe, documenting the `gfverify` component djb mentioned near the end, to verify Curve25519: http://ecc2015.math.u-bordeaux1.fr/documents/schwabe.pdf
Another interesting paper just from there for performance minded people, "Sandy2x: The Fastest Curve25519 Implementation Ever" - http://csrc.nist.gov/groups/ST/ecc-workshop-2015/presentatio...