-- |
-- Module      : Crypto.PubKey.ECC.DH
-- License     : BSD-style
-- Maintainer  : Vincent Hanquez <vincent@snarc.org>
-- Stability   : experimental
-- Portability : unknown
--
-- Elliptic curve Diffie Hellman
module Crypto.PubKey.ECC.DH (
    Curve,
    PublicPoint,
    PrivateNumber,
    SharedKey (..),
    generatePrivate,
    calculatePublic,
    getShared,
) where

import Crypto.Number.Generate (generateMax)
import Crypto.Number.Serialize (i2ospOf_)
import Crypto.PubKey.DH (SharedKey (..))
import Crypto.PubKey.ECC.Prim (pointMul)
import Crypto.PubKey.ECC.Types (
    Curve,
    Point (..),
    PrivateNumber,
    PublicPoint,
    common_curve,
    curveSizeBits,
    ecc_g,
    ecc_n,
 )
import Crypto.Random.Types

-- | Generating a private number d.
generatePrivate :: MonadRandom m => Curve -> m PrivateNumber
generatePrivate :: forall (m :: * -> *). MonadRandom m => Curve -> m PrivateNumber
generatePrivate Curve
curve = PrivateNumber -> m PrivateNumber
forall (m :: * -> *).
MonadRandom m =>
PrivateNumber -> m PrivateNumber
generateMax PrivateNumber
n
  where
    n :: PrivateNumber
n = CurveCommon -> PrivateNumber
ecc_n (CurveCommon -> PrivateNumber) -> CurveCommon -> PrivateNumber
forall a b. (a -> b) -> a -> b
$ Curve -> CurveCommon
common_curve Curve
curve

-- | Generating a public point Q.
calculatePublic :: Curve -> PrivateNumber -> PublicPoint
calculatePublic :: Curve -> PrivateNumber -> PublicPoint
calculatePublic Curve
curve PrivateNumber
d = PublicPoint
q
  where
    g :: PublicPoint
g = CurveCommon -> PublicPoint
ecc_g (CurveCommon -> PublicPoint) -> CurveCommon -> PublicPoint
forall a b. (a -> b) -> a -> b
$ Curve -> CurveCommon
common_curve Curve
curve
    q :: PublicPoint
q = Curve -> PrivateNumber -> PublicPoint -> PublicPoint
pointMul Curve
curve PrivateNumber
d PublicPoint
g

-- | Generating a shared key using our private number and
--   the other party public point.
getShared :: Curve -> PrivateNumber -> PublicPoint -> SharedKey
getShared :: Curve -> PrivateNumber -> PublicPoint -> SharedKey
getShared Curve
curve PrivateNumber
db PublicPoint
qa = ScrubbedBytes -> SharedKey
SharedKey (ScrubbedBytes -> SharedKey) -> ScrubbedBytes -> SharedKey
forall a b. (a -> b) -> a -> b
$ Int -> PrivateNumber -> ScrubbedBytes
forall ba. ByteArray ba => Int -> PrivateNumber -> ba
i2ospOf_ ((Int
nbBits Int -> Int -> Int
forall a. Num a => a -> a -> a
+ Int
7) Int -> Int -> Int
forall a. Integral a => a -> a -> a
`div` Int
8) PrivateNumber
x
  where
    x :: PrivateNumber
x = case Curve -> PrivateNumber -> PublicPoint -> PublicPoint
pointMul Curve
curve PrivateNumber
db PublicPoint
qa of
        Point PrivateNumber
x' PrivateNumber
_ -> PrivateNumber
x'
        PublicPoint
_ -> [Char] -> PrivateNumber
forall a. HasCallStack => [Char] -> a
error [Char]
"getShared"
    nbBits :: Int
nbBits = Curve -> Int
curveSizeBits Curve
curve