Add existing HPKE project files

crypto/ecdh/stubs.go

@@ -0,0 +1,15 @@
+package ecdh
+
+import "crypto/ecdh"
+
+// This file contains stubs to allow importing only this package instead of
+// crypto/ecdh, to minimize the diff.
+
+type Curve = ecdh.Curve
+type PrivateKey = ecdh.PrivateKey
+type PublicKey = ecdh.PublicKey
+
+func X25519() Curve { return ecdh.X25519() }
+func P256() Curve   { return ecdh.P256() }
+func P384() Curve   { return ecdh.P384() }
+func P521() Curve   { return ecdh.P521() }