On 2017-01-11 21:20, Cory Benfield wrote:
>
>> On 11 Jan 2017, at 19:49, Christian Heimes <[email protected]> wrote:
>>
>> AFAIK PyOpenSSL doesn't support this mode. How do we deal with
>> unconnected sockets, UDP/DTLS and other transports? Are sockets limited
>> to AF_INET / AF_INET6 and SOCK_STREAM?
>
> To begin with, I think we need to restrict ourselves to SOCK_STREAM. There’s
> no need to get specific about address family I don’t think. As for
> unconnected sockets, I think I’d like to delay that concern unless someone
> wants to propose the API.
* +1 for SOCK_STREAM
* Although it's obvious to us, we should to state that IPAddress SAN
validation is only defined for AF_INET and AF_INET6.
* Do we need to define blocking / non blocking state of the socket?
* What about STARTTLS support, do we need to define how to deal with
data that has been transmitted before?
Later:
* unconnected socket and tlssocket.connect().
* Python's ssl module has unwrap (STOPTLS) to shutdown a TLS socket and
return to non-encrypted communcation.
>
>> In the not-so-distant future SRV-ID validation will become relevant. In
>> order to support dNSName, IPAddress, and SRV-ID validation, the TLS
>> socket needs the hostname (if available), IP address, port and service
>> type (e.g. http, ldap, xmpp-server, …).
>
> The advantage of this API is that it would be extensible. We can extend it as
> needed over time, we don’t need to shove everything in at once. So I’m
> inclined to want to defer this until we see what the implementations actually
> do.
Maybe we can get away without any extension to the API. SRV-ID uses
underline to signal a service identifier, e.g. _http.www.example.org. In
the future an application could pass down a service identifier as
server_hostname argument and let the TLS library deal with it like this:
if server_hostname.startswith('_'):
srvid = server_hostname
service, hostname = server_hostname.split('.', 1)
service = service[1:]
else:
service = srvid = None
hostname = server_hostname
>> For hostname validation we should also define how we are going to deal
>> with encodings. Is the hostname always a IDN U-label, A-label or can it
>> be both?
>
> Pass. I think you have a better idea of what is required here than I do: do
> you have a suggestion?
OpenSSL's hostname verification code accept IDN A-labels. SubjecAltNames
are encoded as IA5String containing IDN A-labels, too. For most
flexibility the wrap functions should accept server_hostnames as both
U-label and A-label. If you add an encode_hostname() method to the
context, than users can easily override the method to switch between
IDNA 2003, 2008 or perform custom checks to prevent homoglyphic
confusion attacks.
class _BaseContext:
def encode_hostname(self, hostname: str) -> str:
"""Convert IDN U-label to A-label
"""
@abstractmethod
def wrap_socket(self, socket: socket.socket,
auto_handshake=True: bool,
server_hostname=None: Optional[str]):
if server_hostname is not None:
server_hostname = self.context.encode_hostname(
server_hostname)
Christian
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