Test implementation of a CA in Python.

This is mostly intended to be invoked from cryptsuite, so that I can
make test certificates with various features to check the validation
function. But it also has a command-line interface, which currently
contains just enough features that I was able to generate a
certificate and actually make sure OpenSSH accepted it (proving that I
got the format right in this script).

You _could_ expand this script into a full production CA, with a
couple more command-line options, if you didn't mind the slightly
awkward requirement that in command-line mode it insists on doing its
signing via an SSH agent. But for the moment it's only intended for
test purposes.

test/ssh.py

@@ -24,6 +24,9 @@ def ssh_byte(n):
 def ssh_uint32(n):
     return struct.pack(">L", n)
 
+def ssh_uint64(n):
+    return struct.pack(">Q", n)
+
 def ssh_string(s):
     return ssh_uint32(len(s)) + s
 
@@ -53,6 +56,10 @@ def ssh_decode_byte(s):
 def ssh_decode_uint32(s):
     return struct.unpack_from(">L", s, 0)[0], 4
 
+@decoder
+def ssh_decode_uint64(s):
+    return struct.unpack_from(">Q", s, 0)[0], 8
+
 @decoder
 def ssh_decode_string(s):
     length = ssh_decode_uint32(s)