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Require Export Crypto.Spec.CompleteEdwardsCurve.
Require Import Crypto.ModularArithmetic.FField.
Require Import Crypto.ModularArithmetic.FNsatz.
Require Import Crypto.CompleteEdwardsCurve.Pre.
Require Import Crypto.ModularArithmetic.PrimeFieldTheorems.
Require Import Coq.Logic.Eqdep_dec.
Require Import Crypto.Tactics.VerdiTactics.
Section CompleteEdwardsCurveTheorems.
Context {prm:TwistedEdwardsParams}.
Local Opaque q a d prime_q two_lt_q nonzero_a square_a nonsquare_d. (* [F_field] calls [compute] *)
Existing Instance prime_q.
Add Field Ffield_p' : (@Ffield_theory q _)
(morphism (@Fring_morph q),
preprocess [Fpreprocess],
postprocess [Fpostprocess; try exact Fq_1_neq_0; try assumption],
constants [Fconstant],
div (@Fmorph_div_theory q),
power_tac (@Fpower_theory q) [Fexp_tac]).
Add Field Ffield_notConstant : (OpaqueFieldTheory q)
(constants [notConstant]).
Ltac clear_prm :=
generalize dependent a; intro a; intros;
generalize dependent d; intro d; intros;
generalize dependent prime_q; intro prime_q; intros;
generalize dependent q; intro q; intros;
clear prm.
Lemma point_eq : forall p1 p2, p1 = p2 -> forall pf1 pf2,
mkPoint p1 pf1 = mkPoint p2 pf2.
Proof.
destruct p1, p2; intros; find_injection; intros; subst; apply f_equal.
apply UIP_dec, F_eq_dec. (* this is a hack. We actually don't care about the equality of the proofs. However, we *can* prove it, and knowing it lets us use the universal equality instead of a type-specific equivalence, which makes many things nicer. *)
Qed.
Hint Resolve point_eq.
Ltac Edefn := unfold unifiedAdd, unifiedAdd', zero; intros;
repeat match goal with
| [ p : point |- _ ] =>
let x := fresh "x" p in
let y := fresh "y" p in
let pf := fresh "pf" p in
destruct p as [[x y] pf]; unfold onCurve in pf
| _ => eapply point_eq, (f_equal2 pair)
| _ => eapply point_eq
end.
Lemma twistedAddComm : forall A B, (A+B = B+A)%E.
Proof.
Edefn; apply (f_equal2 div); ring.
Qed.
Ltac unifiedAdd_nonzero := match goal with
| [ |- (?op 1 (d * _ * _ * _ * _ *
inv (1 - d * ?xA * ?xB * ?yA * ?yB) * inv (1 + d * ?xA * ?xB * ?yA * ?yB)))%F <> 0%F]
=> let Hadd := fresh "Hadd" in
pose proof (@unifiedAdd'_onCurve _ _ _ _ two_lt_q nonzero_a square_a nonsquare_d (xA, yA) (xB, yB)) as Hadd;
simpl in Hadd;
match goal with
| [H : (1 - d * ?xC * xB * ?yC * yB)%F <> 0%F |- (?op 1 ?other)%F <> 0%F] =>
replace other with
(d * xC * ((xA * yB + yA * xB) / (1 + d * xA * xB * yA * yB))
* yC * ((yA * yB - a * xA * xB) / (1 - d * xA * xB * yA * yB)))%F by (subst; unfold div; ring);
auto
end
end.
Lemma twistedAddAssoc : forall A B C, (A+(B+C) = (A+B)+C)%E.
Proof.
(* The Ltac takes ~15s, the Qed no longer takes longer than I have had patience for *)
Edefn; F_field_simplify_eq; try abstract (rewrite ?@F_pow_2_r in *; clear_prm; F_nsatz);
pose proof (@edwardsAddCompletePlus _ _ _ _ two_lt_q nonzero_a square_a nonsquare_d);
pose proof (@edwardsAddCompleteMinus _ _ _ _ two_lt_q nonzero_a square_a nonsquare_d);
cbv beta iota in *;
repeat split; field_nonzero idtac; unifiedAdd_nonzero.
Qed.
Lemma zeroIsIdentity : forall P, (P + zero = P)%E.
Proof.
Edefn; repeat rewrite ?F_add_0_r, ?F_add_0_l, ?F_sub_0_l, ?F_sub_0_r,
?F_mul_0_r, ?F_mul_0_l, ?F_mul_1_l, ?F_mul_1_r, ?F_div_1_r; exact eq_refl.
Qed.
(* solve for x ^ 2 *)
Definition solve_for_x2 (y : F q) := ((y ^ 2 - 1) / (d * (y ^ 2) - a))%F.
Lemma d_y2_a_nonzero : (forall y, 0 <> d * y ^ 2 - a)%F.
intros ? eq_zero.
pose proof prime_q.
destruct square_a as [sqrt_a sqrt_a_id].
rewrite <- sqrt_a_id in eq_zero.
destruct (Fq_square_mul_sub _ _ _ eq_zero) as [ [sqrt_d sqrt_d_id] | a_zero].
+ pose proof (nonsquare_d sqrt_d); auto.
+ subst.
rewrite Fq_pow_zero in sqrt_a_id by congruence.
auto using nonzero_a.
Qed.
Lemma a_d_y2_nonzero : (forall y, a - d * y ^ 2 <> 0)%F.
Proof.
intros y eq_zero.
pose proof prime_q.
eapply F_minus_swap in eq_zero.
eauto using (d_y2_a_nonzero y).
Qed.
Lemma solve_correct : forall x y, onCurve (x, y) <->
(x ^ 2 = solve_for_x2 y)%F.
Proof.
split.
+ intro onCurve_x_y.
pose proof prime_q.
unfold onCurve in onCurve_x_y.
eapply F_div_mul; auto using (d_y2_a_nonzero y).
replace (x ^ 2 * (d * y ^ 2 - a))%F with ((d * x ^ 2 * y ^ 2) - (a * x ^ 2))%F by ring.
rewrite F_sub_add_swap.
replace (y ^ 2 + a * x ^ 2)%F with (a * x ^ 2 + y ^ 2)%F by ring.
rewrite onCurve_x_y.
ring.
+ intro x2_eq.
unfold onCurve, solve_for_x2 in *.
rewrite x2_eq.
field.
auto using d_y2_a_nonzero.
Qed.
End CompleteEdwardsCurveTheorems.
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