secp256k1

commit f67d1cc5897496eb8ea32b582264f85c02c2418d
parent 78a07bfdf80a67cb2f132c805b7decf333365033
Author: Jared Tobin <jared@jtobin.io>
Date:   Thu, 13 Mar 2025 13:58:33 +0400

lib: ecdh implementation

Diffstat:
M
lib/Crypto/Curve/Secp256k1.hs
 | 
24
++++++++++++++++++++++++

1 file changed, 24 insertions(+), 0 deletions(-)
diff --git a/lib/Crypto/Curve/Secp256k1.hs b/lib/Crypto/Curve/Secp256k1.hs
@@ -42,6 +42,9 @@ module Crypto.Curve.Secp256k1 (
   -- * Serializing
   , serialize_point
 
+  -- * ECDH
+  , ecdh
+
   -- * BIP0340 Schnorr signatures
   , sign_schnorr
   , verify_schnorr
@@ -1236,3 +1239,24 @@ _verify_ecdsa_unrestricted _mul (SHA256.hash -> h) p (ECDSA r s)
                in  v == r
 {-# INLINE _verify_ecdsa_unrestricted #-}
 
+-- ecdh -----------------------------------------------------------------------
+
+-- SEC1-v2 3.3.1
+
+-- | Compute a shared secret, given a secret key and public secp256k1 point,
+--   via Elliptic Curve Diffie-Hellman (ECDH).
+--
+--   The shared secret is the SHA256 hash of the compressed secp256k1
+--   point obtained by scalar multiplication.
+ecdh
+  :: Integer       -- ^ secret key
+  -> Projective    -- ^ public key
+  -> BS.ByteString -- ^ shared secret
+ecdh _SECRET pub
+  | not (ge _SECRET)   = error "ppad-secp256k1 (ecdh): invalid secret key"
+  | otherwise =
+      let pt = mul pub _SECRET
+      in  if   pt == _CURVE_ZERO
+          then error "ppad-secp256k1 (ecdh): invalid public key"
+          else SHA256.hash (serialize_point pt)
+