polish the README and remove my local config from it

README.md

@@ -26,53 +26,87 @@ has not been audited. Try it at your own risk._
 It's written in [Fennel](https://www.fennel-lang.org). To build it
 either use Nix or read [package.nix](package.nix) and figure out how
 to replicate the steps manually.  Note that it requires a patch to the
-luaossl module
+luaossl module.
 
+### CA key and cert
+
+Create the CA key and the certificate used for signing. You will be
+asked a bunch of questions that will be incorporated into the
+certificate: when prompted for "Common Name", say "Certificate
+Authority" or something like that
+
+```
+openssl genrsa -out ca.key 4096
+openssl req  -addext basicConstraints=critical,CA:TRUE,pathlen:1  --x509 -new -nodes -key ca.key -sha256 -days 3650  -out ca.crt
+```
+
+### Server key and cert
+
+The certifix service is exposed over HTTPS, so it needs its own
+certificate signed by the CA. Use your hostname when prompted for
+Common Name
+
+```
+openssl req -newkey rsa:2048 -nodes -keyout server.key --out server.csr
+openssl x509 -req -in server.csr -days 365 -CA ca.crt -CAkey ca.key -CAcreateserial -out server.crt
+```
+
+### Build and start the server
+
+The server needs to be told of all of the preceding files, _plus_ a
+file containing the expected value of the pre-shared key that you want
+it to check client certificate requests against.
 
 ```
-# pick a PSK
 echo 'loves labours lost' > psk
 chmod 0700 psk
+nix-build
+result/bin/certifix  --challenge-password psk  --ca-certificate ca.crt --ca-private-key --server-certificate server.crt --server-private-key server.key localhost:19613
+```
 
-# create CA key and cert used for signing
-openssl genrsa -out ca.key 4096
-CN=CA openssl req -config openssl.cnf -addext basicConstraints=critical,CA:TRUE,pathlen:1  --x509 -new -nodes -key ca.key -sha256 -days 3650  -out ca.crt
+### Try it and see if it works
 
-# create key for the server and sign it with the CA
-CN=localhost openssl req -config openssl.cnf -newkey rsa:2048 -nodes -keyout server.key --out server.csr
-openssl x509 -req -in server.csr -days 365 -CA ca.crt -CAkey ca.key -CAcreateserial -out server.crt
+To set the `challengePassword` attribute in a CSR using OpenSSL, you
+need to create a configuration file.  Copy `openssl.cnf.example` to
+`openssl.cnf` and edit it for your setup.
 
-# create example client CSR for testing (check openssl.cnf against "psk" file)
-CN=rotuer openssl req -config openssl.cnf -newkey rsa:2048 -nodes -keyout client.key -out client.csr
+* the values in `req_distinguished_name` should match your organisation
+* the `challengePassword` attribute must match whatever you told the
+ service to expect (`psk` file in the preceding step)
 
-# build and start the server
-nix-build && result/bin/certifix  --challenge-password psk  --ca-certificate ca.crt --ca-private-key --server-certificate server.crt --server-private-key server.key localhost:19613
-# send it
+```
+# make CSR
+CN=mydevice openssl req -config openssl.cnf -newkey rsa:2048 -nodes -keyout client.key -out client.csr
+
+# send it to certifix, should get a certificate in response
 curl --cacert ca.crt   -v -H 'content-type: application/x-pem-file' --data-binary @client.csr  https://localhost:19613/sign
 ```
 
+
 ## Reasons this is not secure
 
-* the CA key is present in the memory of the process that reads and
-parses network requests
+* the CA key is readable by and present in the memory of the process
+that reads and parses network requests. Bearing in mind the the whole
+point is to automate signing we can only do so much about this, but at
+least we could move the actual signing to a separate process which is
+only invoked once an acceptable request has been received.
 
-* there is no "intermediate" key: requests are signed by the root key
+* there is no intermediate key - the requests are signed directly by the root CA
 
 * I haven't checked that the protocols or the ciphers are restricted
-to modern and sensible defaults
+  to modern and sensible defaults
 
 * doesn't set 4.2.1.6.  Subject Alternative Name
 
 * doesn't set Key Usage extension (https://www.rfc-editor.org/rfc/rfc5280#section-4.2.1.3)
 
+* probably has wrong basicConstraints in CA cert
+
 * likewise other TLS best practices
 
 
-
-
-
 ## Background
 
 
-
 * [RFC 5967 - spec for a CSR](https://datatracker.ietf.org/doc/html/rfc5967)
+* [A gentle introduction to ASN1. and DER](https://letsencrypt.org/docs/a-warm-welcome-to-asn1-and-der/)