XXX "To force a complete SSL/TLS session renegotiation, the
current session should be invalidated prior to calling this
method." Translation: must call Session.invalidate();
Construct a line consisting of a prefix, followed by a space,
followed by a base64-encoded binary value, followed by a space,
followed by a positive integer value.
Write a serialized SignedList into the store, after validating
its digital signature and verifying that it is more recent than
any pre-existing SignedList with the same title key.