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BSD-3-Clause
ECurve.Curve

Contains curve definitions, utility functions for retrieving said definitions, and a function for determining if point is on the curve
Standard definitions of elliptic curves
getCurve : CurveType -> Models.Curve
Gets a curve for a given curve type
new : BigInt -> BigInt -> BigInt -> BigInt -> BigInt -> BigInt -> BigInt -> Curve
Returns a new elliptic curve from points
isOnCurve : Curve -> Point -> Bool
Checks if point is on a curve
module ECurve.Curve exposing (..)

{-| Contains curve definitions,
utility functions for retrieving said definitions,
and a function for determining if point is on the curve

@docs CurveType, getCurve, new, isOnCurve

-}

import ECurve.Point as Point exposing (affineX, affineY)
import BigInt exposing (BigInt, add, mul, mod, fromString, pow)
import ECurve.Util exposing (zero, bitLength, str, signum, square, three)
import ECurve.Models as Models exposing (Point, Curve)

{-| Standard definitions of elliptic curves
-}
type CurveType
    = Secp128r1
    | Secp160k1
    | Secp160r1
    | Secp192k1
    | Secp192r1
    | Secp256k1
    | Secp256r1

{-| Gets a curve for a given curve type
-}
getCurve : CurveType -> Models.Curve
getCurve curve =
    case curve of
        Secp128r1 ->
            new (str "340282366762482138434845932244680310783") (str "340282366762482138434845932244680310780") (str "308990863222245658030922601041482374867") (str "340282366762482138443322565580356624661") (str "1") (str "29408993404948928992877151431649155974") (str "275621562871047521857442314737465260675")

        Secp160k1 ->
            new (str "1461501637330902918203684832716283019651637554291") (str "0") (str "7") (str "1461501637330902918203686915170869725397159163571") (str "1") (str "338530205676502674729549372677647997389429898939") (str "842365456698940303598009444920994870805149798382")

        Secp160r1 ->
            new (str "1461501637330902918203684832716283019653785059327") (str "1461501637330902918203684832716283019653785059324") (str "163235791306168110546604919403271579530548345413") (str "1461501637330902918203687197606826779884643492439") (str "1") (str "425826231723888350446541592701409065913635568770") (str "203520114162904107873991457957346892027982641970")

        Secp192k1 ->
            new (str "6277101735386680763835789423207666416102355444459739541047") (str "0") (str "3") (str "6277101735386680763835789423061264271957123915200845512077") (str "1") (str "5377521262291226325198505011805525673063229037935769709693") (str "3805108391982600717572440947423858335415441070543209377693")

        Secp192r1 ->
            new (str "6277101735386680763835789423207666416083908700390324961279") (str "6277101735386680763835789423207666416083908700390324961276") (str "2455155546008943817740293915197451784769108058161191238065") (str "6277101735386680763835789423176059013767194773182842284081") (str "1") (str "602046282375688656758213480587526111916698976636884684818") (str "174050332293622031404857552280219410364023488927386650641")

        Secp256k1 ->
            new (str "115792089237316195423570985008687907853269984665640564039457584007908834671663") (str "0") (str "7") (str "115792089237316195423570985008687907852837564279074904382605163141518161494337") (str "1") (str "55066263022277343669578718895168534326250603453777594175500187360389116729240") (str "32670510020758816978083085130507043184471273380659243275938904335757337482424")

        Secp256r1 ->
            new (str "115792089210356248762697446949407573530086143415290314195533631308867097853951") (str "115792089210356248762697446949407573530086143415290314195533631308867097853948") (str "41058363725152142129326129780047268409114441015993725554835256314039467401291") (str "115792089210356248762697446949407573529996955224135760342422259061068512044369") (str "1") (str "48439561293906451759052585252797914202762949526041747995844080717082404635286") (str "36134250956749795798585127919587881956611106672985015071877198253568414405109")

{-| Returns a new elliptic curve from points
-}
new : BigInt -> BigInt -> BigInt -> BigInt -> BigInt -> BigInt -> BigInt -> Curve
new p a b n h gx gy =
    let
        c =
            { p = p
            , a = a
            , b = b
            , g = Point.new p a zero zero zero
            , n = n
            , h = h
            , pLength = 0
            }

        g =
            Point.fromAffine p a gx gy

        pLength =
            ((bitLength p) + 7) // 8

        cc =
            { c | g = g, pLength = pLength }
    in
        cc

{-| Checks if point is on a curve
-}
isOnCurve : Curve -> Point -> Bool
isOnCurve curve q =
    let
        x =
            affineX q

        y =
            affineY q

        a =
            curve.a

        b =
            curve.b

        p =
            curve.p

        result =
            if signum x == LT || BigInt.compare x p == GT || BigInt.compare x p == EQ then
                False
            else if signum y == LT || BigInt.compare y p == GT || BigInt.compare y p == EQ then
                False
            else
                -- check that y^2 = x^3 + ax + b (mod p)
                let
                    lhs =
                        mod (square y) p

                    rhs =
                        mod (add (add (pow x three) (mul a x)) b) p
                in
                    BigInt.compare lhs rhs == EQ
    in
        result