Say the user wants to create a NewEntity, then Serialize the private and public keys. Then call Encrypt. The Hash used first for Encrypt will be `RIPEMD160`, which is not compiled in by default. So say they _specifically_ pass crypto.SHA256 as the Default hash to NewEntity, this should set the PreferredHash in the SelfSignature so they can be encrypted with that hash. Related to golang/go#12153 Change-Id: I3d89f9d60f9abb29ec8365f81da38b8cd0594587 Reviewed-on: https://go-review.googlesource.com/23209 Reviewed-by: Adam Langley <agl@golang.org>