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+# p11p design
+
+## Overview and design criterias
+
+    User application --(dlopen)-->
+    p11p-client.so --(<our-protocol>-over-unix-socket)-->
+    p11p-daemon --(fork+exec, stdin/stdout)-->
+    p11p-helper --(dlopen)-->
+	$vendor.so --(vendor-specific)-->
+	PKCS #11 token
+
+- Typical sequence of events
+  - User application dlopens `p11p-client.so` as a "Cryptoki library"
+  - `p11p-client.so` connects to `p11p-daemon` running on the same
+    system, over a unix socket (AF_UNIX).
+  - `p11p-daemon` forks a process and executes `p11p-helper`
+  - `p11p-helper` dlopens the appropriate Cryptoki library from
+    $vendor and forwards the Cryptoki calls there
+
+- The daemon, `p11p-daemon`, handles both load balancing and failover,
+  according to configuration per (set of) token(s).
+- Run on reasonable Linux and BSD systems.
+- Somewhat isolating (and potentially constraining) the running of
+  vendor solibs by forking before loading them.
+- The Cryptoki stub library, `p11p-client.so`, is implemented in
+  C. TBD: Use code from p11-kit for this? p11-kit-client.so uses
+  libffi and its own serialisation code (rpc-message.c),
+  both of which might be unnecessarily complex, but for a PoC might
+  be a good choice.
+- The daemon, `p11p-daemon`, is implemented in something not too
+  crazy, like Erlang or Rust, taking the deployment story into
+  account -- being self-contained is a worthwhile goal.
+- The daemon child, `p11p-helper`, is an executable program using
+  the Cryptoki API, implemented in C (or possibly another language
+  that can dlopen and call into the vendor solib).
+- Wire protocol between `p11p-client.so` and `p11p-daemon` is TBD but
+  should be designed for simple parsing in C. It runs over an AF_UNIX
+  socket and needs only serialisation of Cryptoki calls -- no
+  addressing and minimal framing (like a message length). TBD:
+  Serialise (using Trunnel) and use an end-of-record sequence instead?
+
+### PKCS #11
+
+#### Supported PKCS #11 mechanisms
+
+TBD
+
+## Configuration
+
+TODO
+
+## External dependencies
+
+TODO
+
+## External documentation
+
+- [OASIS PKCS 11 TC](https://www.oasis-open.org/committees/tc_home.php?wg_abbrev=pkcs11)