diffs

added:

• ecdh module
• thicc readme
• fn to compute shared secret over a FiniteField and CurveGroup
• fn to compute point pair wrt tripartite ecdh over PlutoScalarField and Pluto*Curve types
• fn to compute tripartite shared secret over PlutoScalarField and Pluto*Curve types

notes:

i used PlutoScalarField and Pluto*Curve types bc the pairing fn takes a finer type than CurveGroup. maybe there's a better type to use?

also, base ecdh passes smoke check, tp_ecdh does not. perhaps it's a math bug on my end? it's computed atm as follows.

$$a, b, c \in \mathbb{F}_p$$

$$[a]P, [b]P, [c]P \in E(\mathbb{F}_p)$$

$$[a]Q, [b]Q, [c]Q \in E(\mathbb{F}_{p^2})$$

$$e([b]P, [c]Q)^a = e([a]P, [c]Q)^b = e([a]P, [b]Q)^c$$

closes #81