22 Nov
2005
22 Nov
'05
6:05 p.m.
Hi Klaus,
Klaus Darilion wrote:
The properties (subject: common name, Issuer ...)
right.
Is'nt is a valid scenario that the TLS connection may dropped (for
whatever reason) during an ongoing transaction and thus, the TLS
connection must be re-established for the replies?
yes it's a valid scenario. If so you cannot relay on any transaction
related data as you may choose to statelessly forward the request.
Sounds bloated but in this case you need to store it in VIA also :-/ - i
really don;t like the idea :(
maybe this should be a configurable option.....at least on our side......
regards,
bogdan
Bogdan-Andrei Iancu wrote:
Where is the missing link?
Is it possible to retrieve the tcp_connection from which a SIP message
was received? If yes, we should be able to get the SSL object
(tcp_connection->extra_data).
Is it possible to retrieve the certificate porpierties if we have the
SSL obejct?
yes - this is possible - make available info about the connection
evolved even if it's new one or a re-used one.
Klaus Darilion wrote:
ACK
Hi all!
There are several scenarios where TLS will be used to interconnect
SIP proxies. (open)ser's TLS implementation should be generic enough
to handle all the useful scenarios. Thus, to better understand the
requirements, first I present some examples where (open)ser+TLS will
be useful. (I do not propose which of the following interconnect
models are good or bad. However, openser should be capable to handle
all of them, best in a mixed mode).
Enterprise scenario:
A company uses TLS to interconnect their SIP proxies via public
Internet. The proxies import the companies selfsigned CA-cert as
trusted CAs. The proxies trust other proxies as soon as their cert
is validated using the root CA.
This is already possible using openser 1.0.0 (= or ser+experimental
TLS)
Federation scenario:
Some ITSPs form a federation. The federation-CA signs the certs of
the ITSPs. Here, the validation is like in the enterprise scenario.
(open)ser validates against the federations CA-cert. This works with
openser 1.0.0 as long as the ITSP is only in one federation, or uses
different egress/ingress points for each federation. If the ITSP is
member of two federations and uses one egress/ingress proxy, it has
to decide which certificate it should present to the peer. The
originating proxy could choose the proper client certificate for
example by using a table like (or having the certificate as blob
directly in the DB):
dst_domain certificate
sip.atlanta.com /etc/openser/federationAcert.pem
sip.biloxy.com /etc/openser/federationBcert.pem
sip.chicago.com /etc/openser/federationAcert.pem
Presenting the proper server certificate, is more difficult. The
server does not know if the incoming TLS request belongs to a member
of fedA, fedB or someone else. Thus, presenting the wrong
certificate will lead to the clients rejecting the certificate due
to failed validation. One solution would be sending the
"trusted_ca_keys" (TLS extension) in Client Hello. Unfortunatelly
this is not supported in openssl (and gnutls). Any workaround for this?
As I understood from Cesc, gnutls already support this extension, but
to migrate to gnutls and restart all testing may not pay the effort
as time as it's just a matter of time until the extension will be
also available in openssl.
As temporary solution I will suggest to go by default without the
extension patch, but to provide the patch into the TLS directory and
people interested in these multi-domain scenarios will have to apply
and recompile the openssl lib. And maybe we should do some lobby
(read pressure) on the openssl mailing list in order to push this
extension in the official tree.
Anyway, in this scenario it is important to have the certificate
parameters (Subject, Issuer) available in the routing logic to make
routing decisions based on the TLS authenticaten and adding them to
the CDRs (e.g. via AVPs and extra accounting)
interesting but there might be some problems - the information you
want to log comes from transport layer and you try you log it by
using mechanism from the SIP level. It will works, but the info will
be actually available only for requests that initiated the TLS
connection (send or received) and not also for the requests that
reuse the connection.
Bilateral scenario:
An ITSP has bilateral trust relationships. Each ITSP has its own CA
which signs the certs of this ITSP. If another ITSP wants to trust
this ISTP it only has to import the others CA-cert. This works
already with openser 1.0.0, but exporting the cert parameters for
extra accounting will be useful.
not sure what you mean by cert parameters....... Hosted
SIP scenario:
An ITSP hosts multiple SIP domains for its customers. If the server
has to offer a certificate which includes the proper SIP domain, the
server_name extension is needed to indicate the requested domain in
the client_hello request. Then the server will present the proper
certificate and domain validation (Subject domain == SIP domain) in
the client will succeed.
the solution will also the mighty extension, indeed.....
This will work fine with initial (out-of-dialog)
requests as they
usually will include the SIP domain in the request URI. There will
be problems for responses and in-dialog requests as usually the
Record-Route and Via headers only includes IP addresses. Thus, the
SIP proxy either has to insert the SIP domain into Via and
Record-Route,
or the domain validation should only be done for in-dialog requests.
I don't thing we should worry about replies - they will return via
same connexion - the expiration time of a tcp connection must be
higher than the expiration time of a transaction.. But about the
within the dialog requests - you have a strong case
here!! But is actually more complex : you need to know the inbound
and outbound domains actually - if you received the request from
another peer via TLS and fed it also via TLS to another peer
(relaying) will need to remember both domains since the within the
dialog request may flow in both directions ;).
Maybe storing the domain names as RR param is the simplest and uglier
solution...in the mean while I think is the only one without
involving any dialog persistence.
As workaround (IMO this is a bug in RFC3261) I would validate domains
only for out-of-dialog request.