[pyOpenSSL] How can I verify client that the client is signed by me?

[Jean-Paul Calderone]

On Wed, 17 Sep 2008 20:01:30 +0200, Sebastian Greatful <sebastianthegreatful at gmail.com> wrote:
>I'm building a ssl tcp server using the code below. However I'm unsure about
>how to actually verify the client's cert.
>
>50 class SSLTCPServer(TCPServer):
>
> 51         keyFile = "sslcert/server.key"
>
> 52         certFile = "sslcert/server.crt"
>
> 53         def __init__(self, server_address, RequestHandlerClass):
>
> 54                 ctx = SSL.Context(SSL.SSLv23_METHOD)
>
> 55                 ctx.use_privatekey_file(self.keyFile)
>
> 56                 ctx.use_certificate_file(self.certFile)
>
> 57                 ctx.set_verify(SSL.VERIFY_PEER |
>SSL.VERIFY_FAIL_IF_NO_PEER_CERT | SSL.VERIFY_CLIENT_ONCE, self._verify)
>
> 58                 ctx.set_verify_depth(10)
>
> 59                 ctx.set_session_id('DFS')
>
> 60
>
> 61                 self.server_address = server_address
>
> 62                 self.RequestHandlerClass = RequestHandlerClass
>
> 63                 self.socket = socket.socket(self.address_family,
>self.socket_type)
>
> 64                 self.socket = SSL.Connection(ctx, self.socket)
>
> 65                 self.socket.bind(self.server_address)
>
> 66                 self.socket.listen(self.request_queue_size)
>
> 67
>
> 68         def _verify(self, conn, cert, errno, depth, retcode):
>
> 69                 return not cert.has_expired() and
>cert.get_issuer().organizationName == 'DFS'
>
>Anyone got an idea about how to actually build the _verify method?
>

If you want to make sure the client's certificate is signed by a particular
key which your server has, then you should specify that key's corresponding
certificate as a trusted CA certificate (with a method of the context object,
perhaps load_verify_locations, though there are a bunch of functions which
do similar things, the correct one for you may depend on some other factors).

Then, make sure you respect OpenSSL's decision in the verify callback.  This
is given by the `retcode` parameter.  If the client's certificate is not
signed by a certificate you told the context object to consider a trusted CA
certificate, `retcode` will be false.  You can add whatever additional
checks you want on top of that (ie, for the subject's name or what have you)
but if `retcode` is false, you should return false from the verify function.

This includes things like expiration checking, so you don't need to do that.

Jean-Paul