initial addition of essential crypto, encoders, workflows and LLM instructions

pkg/crypto/ec/secp256k1/ecdh.go

@@ -0,0 +1,21 @@
+// Copyright (c) 2015 The btcsuite developers
+// Copyright (c) 2015-2023 The Decred developers
+// Use of this source code is governed by an ISC
+// license that can be found in the LICENSE file.
+
+package secp256k1
+
+// GenerateSharedSecret generates a shared secret based on a secret key and a
+// public key using Diffie-Hellman key exchange (ECDH) (RFC 5903).
+// RFC5903 Section 9 states we should only return x.
+//
+// It is recommended to securely hash the result before using as a cryptographic
+// key.
+func GenerateSharedSecret(seckey *SecretKey, pubkey *PublicKey) []byte {
+	var point, result JacobianPoint
+	pubkey.AsJacobian(&point)
+	ScalarMultNonConst(&seckey.Key, &point, &result)
+	result.ToAffine()
+	xBytes := result.X.Bytes()
+	return xBytes[:]
+}