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Merge pull request #1953 from andres-erbsen/weier2
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Update Curves/Weierstrass
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andres-erbsen committed Sep 5, 2024
2 parents 9158342 + 6f13372 commit d3af796
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66 changes: 59 additions & 7 deletions src/Curves/Weierstrass/Affine.v
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@@ -1,20 +1,72 @@
Require Import Crypto.Spec.WeierstrassCurve.
Require Import Crypto.Algebra.Field.
Require Import Crypto.Util.Decidable Crypto.Util.Tactics.DestructHead Crypto.Util.Tactics.BreakMatch.
Require Import Crypto.Util.Tactics.SetoidSubst.
Import RelationClasses Morphisms.

Module W.
Section W.
Context {F Feq Fzero Fone Fopp Fadd Fsub Fmul Finv Fdiv} {a b:F}
{field:@Algebra.Hierarchy.field F Feq Fzero Fone Fopp Fadd Fsub Fmul Finv Fdiv}
{Feq_dec:DecidableRel Feq}.
Local Infix "+" := Fadd. Local Infix "-" := Fsub.
Local Infix "*" := Fmul. Local Infix "/" := Fdiv.
Local Notation "x ^ 2" := (x*x) (at level 30).
Local Notation point := (@W.point F Feq Fadd Fmul a b).

Program Definition opp (P:@W.point F Feq Fadd Fmul a b) : @W.point F Feq Fadd Fmul a b
:= match W.coordinates P return F*F+_ with
| inl (x1, y1) => inl (x1, Fopp y1)
| inr tt => inr tt
end.
Next Obligation.
cbv [W.coordinates]; break_match; trivial; fsatz.
Definition opp (P : point) : point. refine (exist _ (
match W.coordinates P with
| inl (x1, y1) => inl (x1, Fopp y1)
| inr tt => inr tt
end) _).
Proof. abstract (cbv [W.coordinates]; break_match; trivial; fsatz). Defined.

Global Instance Equivalence_eq : Equivalence (@W.eq _ Feq Fadd Fmul a b).
Proof.
cbv [W.eq W.coordinates]; split; repeat intros [ [ []|[] ] ?]; intuition try solve
[contradiction | apply reflexivity | apply symmetry; trivial | eapply transitivity; eauto 1].
Qed.

Global Instance Proper_opp : Proper (W.eq ==> W.eq) opp.
Proof.
repeat (intros [ [[]|[] ]?] || intro); cbv [W.coordinates opp W.eq] in *;
repeat (try destruct_head' @and; try case dec as []; try contradiction; try split); trivial.
setoid_subst_rel Feq; reflexivity.
Qed.

(* Weierstraß Elliptic Curves and Side-Channel Attacks
by Eric Brier and Marc Joye, 2002 *)
Definition add' (P1 P2 : point) : point. refine (exist _
match W.coordinates P1, W.coordinates P2 with
| inl (x1, y1), inl (x2, y2) =>
if dec (Feq y1 (Fopp y2)) then
if dec (Feq x1 x2) then inr tt
else let k := (y2-y1)/(x2-x1) in
let x3 := k^2-x1-x2 in
let y3 := k*(x1-x3)-y1 in
inl (x3, y3)
else let k := ((x1^2 + x1*x2 + x2^2 + a)/(y1+y2)) in
let x3 := k^2-x1-x2 in
let y3 := k*(x1-x3)-y1 in
inl (x3, y3)
| inr tt, inr tt => inr tt
| inr tt, _ => W.coordinates P2
| _, inr tt => W.coordinates P1
end _).
Proof. abstract (cbv [W.coordinates]; break_match; trivial; fsatz). Defined.

Lemma add'_correct char_ge_3 : forall P Q : point, W.eq (W.add' P Q) (W.add(char_ge_3:=char_ge_3) P Q).
Proof. intros [ [[]|]?] [ [[]|]?]; cbv [W.coordinates W.add W.add' W.eq]; break_match; try split; try fsatz. Qed.

Global Instance Proper_add' : Proper (W.eq ==> W.eq ==> W.eq) add'.
Proof.
repeat (intros [ [[]|[] ]?] || intro); cbv [W.coordinates W.add' W.eq] in *;
repeat (try destruct_head' @and; try case dec as []; try contradiction; try split); trivial.
Time par : fsatz. (* setoid_subst_rel is slower *)
Qed.

Global Instance Proper_add {char_ge_3} :
Proper (W.eq ==> W.eq ==> W.eq) (@W.add _ Feq Fzero Fone Fopp Fadd Fsub Fmul Finv Fdiv _ _ char_ge_3 a b).
Proof. repeat intro. rewrite <-2add'_correct. apply Proper_add'; trivial. Qed.
End W.
End W.
87 changes: 54 additions & 33 deletions src/Curves/Weierstrass/Jacobian/CoZ.v
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Expand Up @@ -24,7 +24,7 @@ Module Jacobian.
Local Infix "+" := Fadd. Local Infix "-" := Fsub.
Local Infix "*" := Fmul. Local Infix "/" := Fdiv.
Local Notation "x ^ 2" := (x*x). Local Notation "x ^ 3" := (x^2*x).
Local Notation "2" := (1+1). Local Notation "4" := (2+2).
Local Notation "2" := (1+1). Local Notation "4" := (1+1+1+1).
Local Notation "8" := (4+4). Local Notation "27" := (4*4 + 4+4 +1+1+1).
Local Notation Wpoint := (@W.point F Feq Fadd Fmul a b).
Context {char_ge_12:@Ring.char_ge F Feq Fzero Fone Fopp Fadd Fsub Fmul 12%positive}
Expand Down Expand Up @@ -67,8 +67,8 @@ Module Jacobian.
| _ => progress destruct_head'_sum
| _ => progress destruct_head'_bool
| _ => progress destruct_head'_or
| H: context[@dec ?P ?pf] |- _ => destruct (@dec P pf)
| |- context[@dec ?P ?pf] => destruct (@dec P pf)
| H: context[@dec ?P ?pf] |- _ => destruct (@dec P pf) || destruct (@dec P pf) at 1
| |- context[@dec ?P ?pf] => destruct (@dec P pf) || destruct (@dec P pf) at 1
| |- ?P => lazymatch type of P with Prop => split end
end.
Ltac prept := repeat prept_step.
Expand Down Expand Up @@ -405,36 +405,57 @@ Module Jacobian.
end;
fsatz ].

Hint Unfold Jacobian.double negb andb : points_as_coordinates.
Hint Unfold W.eq W.add Jacobian.to_affine Jacobian.of_affine Jacobian.add Jacobian.add_impl Jacobian.opp : points_as_coordinates.

(* These could go into Jacobian.v *)
Global Instance Proper_opp : Proper (eq ==> eq) opp. Proof. faster_t_noclear. Qed.
Local Hint Unfold W.add W.add' W.zero W.opp : points_as_coordinates.
Local Hint Unfold Jacobian.double Jacobian.double_impl negb andb : points_as_coordinates.
Local Hint Unfold Jacobian.to_affine Jacobian.to_affine_impl Jacobian.of_affine Jacobian.of_affine_impl Jacobian.add Jacobian.add_impl Jacobian.opp : points_as_coordinates.

Lemma of_affine_add P Q
: eq (of_affine (W.add P Q)) (add (of_affine P) (of_affine Q)).
Proof. t. Qed.

Lemma add_opp (P : point) :
z_of (add P (opp P)) = 0.
Proof. faster_t_noclear. Qed.
Proof. rewrite Jacobian.eq_iff, Jacobian.to_affine_add, 3Jacobian.to_affine_of_affine; reflexivity. Qed.

Lemma add_comm (P Q : point) :
eq (add P Q) (add Q P).
Proof. faster_t_noclear. Qed.
Proof.
pose proof W.commutative_group(discriminant_nonzero:=discriminant_nonzero) _.
rewrite Jacobian.eq_iff, 2Jacobian.to_affine_add.
rewrite Hierarchy.commutative. reflexivity.
Qed.

Lemma add_zero_l (P Q : point) (H : z_of P = 0) :
eq (add P Q) Q.
Proof. faster_t. Qed.
Proof.
pose proof W.commutative_group(discriminant_nonzero:=discriminant_nonzero) _.
rewrite Jacobian.eq_iff, Jacobian.to_affine_add.
rewrite (proj1 (Jacobian.iszero_iff P)), Hierarchy.left_identity; [reflexivity|].
case P as [ [ []?] ?]; cbv [Jacobian.iszero z_of proj1_sig snd] in *; trivial.
Qed.

Lemma add_zero_r (P Q : point) (H : z_of Q = 0) :
eq (add P Q) P.
Proof. faster_t. Qed.
Proof. rewrite add_comm, add_zero_l; trivial; reflexivity. Qed.

Lemma add_double (P Q : point) :
eq P Q ->
eq (add P Q) (double P).
Proof. faster_t_noclear. Qed.
Proof.
rewrite 2Jacobian.eq_iff, Jacobian.to_affine_add, Jacobian.to_affine_double.
intros ->; reflexivity.
Qed.

Lemma add_opp_same_r (P : point) :
eq (add P (opp P)) (of_affine W.zero).
Proof.
pose proof W.commutative_group(discriminant_nonzero:=discriminant_nonzero) _.
rewrite Jacobian.eq_iff, Jacobian.to_affine_add, Jacobian.to_affine_of_affine, Jacobian.to_affine_opp.
rewrite Hierarchy.right_inverse. reflexivity.
Qed.

Lemma z_of_eq_zero (P : point) : eq P (of_affine W.zero) -> z_of P = 0.
Proof. prept. match goal with H : 0 <> 0 |- _ => case (H ltac:(reflexivity)) end. Qed.

Lemma z_of_add_opp_same_r (P : point) :
z_of (add P (opp P)) = 0.
Proof. apply z_of_eq_zero, add_opp_same_r. Qed.

(* This uses assumptions not present in Jacobian.v,
namely char_ge_12 and discriminant_nonzero. *)
Expand Down Expand Up @@ -465,7 +486,7 @@ Module Jacobian.

Lemma opp_co_z (P : point) :
co_z P (opp P).
Proof. unfold co_z; faster_t. Qed.
Proof. unfold co_z. prept. Qed.

Program Definition make_co_z (P Q : point) (HQaff : z_of Q = 1) : point*point :=
match proj1_sig P, proj1_sig Q return (F*F*F)*(F*F*F) with
Expand All @@ -479,8 +500,8 @@ Module Jacobian.
let t2 := t3 * t2 in
(P, (t1, t2, t3))
end.
Next Obligation. Proof. faster_t. Qed.
Next Obligation. Proof. faster_t. Qed.
Next Obligation. Proof. prept. Qed.
Next Obligation. Proof. prept. par: faster_t. Qed.

Hint Unfold is_point co_z make_co_z : points_as_coordinates.

Expand Down Expand Up @@ -520,17 +541,17 @@ Module Jacobian.
let t5 := t5 - t2 in
((t4, t5, t3), (t1, t2, t3))
end.
Next Obligation. Proof. faster_t_noclear. Qed.
Next Obligation. Proof. faster_t. Qed.
Next Obligation. Proof. prept. all : faster_t_noclear. Qed.
Next Obligation. Proof. prept. all : faster_t. Qed.

Hint Unfold zaddu : points_as_coordinates.
Hint Unfold zaddu Jacobian.add_nz_nz : points_as_coordinates.

(* ZADDU(P, Q) = (P + Q, P) if P <> Q, Q <> -P *)
Lemma zaddu_correct (P Q : point) (H : co_z P Q)
(Hneq : x_of P <> x_of Q):
let '(R1, R2) := zaddu P Q H in
eq (add P Q) R1 /\ eq P R2 /\ co_z R1 R2.
Proof. faster_t_noclear. Qed.
Proof. prept. par : faster_t_noclear. Qed.

Lemma zaddu_correct_alt (P Q : point) (H : co_z P Q) :
let '(R1, R2) := zaddu P Q H in
Expand All @@ -546,7 +567,7 @@ Module Jacobian.
Lemma zaddu_correct0 (P : point) :
let '(R1, R2) := zaddu P (opp P) (opp_co_z P) in
z_of R1 = 0 /\ co_z R1 R2.
Proof. faster_t_noclear. Qed.
Proof. prept. all : faster_t_noclear. Qed.

(* Scalar Multiplication on Weierstraß Elliptic Curves from Co-Z Arithmetic *)
(* Goundar, Joye, Miyaji, Rivain, Vanelli *)
Expand Down Expand Up @@ -587,16 +608,16 @@ Module Jacobian.
let t2 := t2 + t6 in
((t1, t2, t3), (t4, t5, t3))
end.
Next Obligation. Proof. faster_t_noclear. Qed.
Next Obligation. Proof. faster_t_noclear. Qed.
Next Obligation. Proof. prept. all : faster_t_noclear. Qed.
Next Obligation. Proof. prept. all : faster_t_noclear. Qed.

Hint Unfold zaddc : points_as_coordinates.
(* ZADDC(P, Q) = (P + Q, P - Q) if P <> Q, Q <> -P *)
Lemma zaddc_correct (P Q : point) (H : co_z P Q)
(Hneq : x_of P <> x_of Q):
let '(R1, R2) := zaddc P Q H in
eq (add P Q) R1 /\ eq (add P (opp Q)) R2 /\ co_z R1 R2.
Proof. faster_t_noclear. Qed.
Proof. prept. par : faster_t_noclear. Qed.

Lemma zaddc_correct_alt (P Q : point) (H : co_z P Q) :
let '(R1, R2) := zaddc P Q H in
Expand Down Expand Up @@ -735,7 +756,7 @@ Module Jacobian.
rewrite add_assoc, add_comm. reflexivity.
- rewrite <- A2, <- B1, <- B2.
rewrite (add_comm P Q).
rewrite add_assoc. rewrite add_zero_r; [reflexivity|apply add_opp].
rewrite add_assoc. rewrite add_zero_r; [reflexivity|apply z_of_add_opp_same_r].
Qed.

Lemma zdau_naive_correct_alt (P Q : point) (H : co_z P Q)
Expand All @@ -756,7 +777,7 @@ Module Jacobian.
rewrite add_assoc, add_comm. reflexivity.
- rewrite <- A2, <- B1, <- B2.
rewrite (add_comm P Q).
rewrite add_assoc. rewrite add_zero_r; [reflexivity|apply add_opp].
rewrite add_assoc. rewrite add_zero_r; [reflexivity|apply z_of_add_opp_same_r].
Qed.

(* Scalar Multiplication on Weierstraß Elliptic Curves from Co-Z Arithmetic *)
Expand Down Expand Up @@ -816,16 +837,16 @@ Module Jacobian.
let t5 := t7 - t5 in
((t1, t2, t3), (t4, t5, t3))
end.
Next Obligation. Proof. faster_t_noclear. Qed.
Next Obligation. Proof. faster_t_noclear. Qed.
Next Obligation. Proof. prept. par:setoid_subst_rel Feq; faster_t_noclear. Qed.
Next Obligation. Proof. prept. par:faster_t_noclear. Qed.

Hint Unfold zdau : points_as_coordinates.

Lemma zdau_naive_eq_zdau (P Q : point) (H : co_z P Q) :
let '(R1, R2) := zdau_naive P Q H in
let '(S1, S2) := zdau P Q H in
eq R1 S1 /\ eq R2 S2.
Proof. faster_t. all: try fsatz. Qed.
Proof. prept. par : faster_t; try fsatz. Qed.

(* Direct proof is intensive, which is why we need the naive implementation *)
Lemma zdau_correct (P Q : point) (H : co_z P Q)
Expand Down
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