Dears SIP wg participants,
You may be surprised that I come to comment the
draft-ietf-sip-dtls-srtp-framework-02 at this point in time - I am also!
Anyway, my comment is about DTLS protocol compliance and the use of
self-signed certificates. Maybe there are things I don't see, but I
wonder if the envisioned use of self-signed certificates is compliant
with DTLS, even assuming the "legitimacy" of accepting self-signed
certificates without a strong trust base in the PKI spirit.
Here are the technical details. I assume the DTLS server protocol entity
"S" wishes to accept either "self-signed" EE certificates or
certificates issued by a couple of trusted CA (requirement R-EXISTING).
"S" would send a DTLS certificate request message containing either an
empty list of CA distinguished names (meaning "I accept any CA") of a
list of CA distinguished name (meaning "I trust these CAs"). In the
latter case, the DTLS client protocol entity "C" would not be allowed to
send a self-signed EE certificate. In the former case, "C" would be
allowed to send any certificate it has on hand, including a self-signed
EE certificate.
There are two alternate adjustments to the draft I see that would
improve its technical quality if the above paragraph is correct:
A) State explicitly that the empty list of CA distinguished names (in
DTLS certificate request messages) option applies. It is then preferable
to describe the self-signed EE certificate as a special case of e.g.
"any X.509 security certificate holding a public key that the end entity
controls (of which the end entity controls the private key counterpart)".
B) Specify a public domain private key value (i.e. breached, snake-oil,
meaningless ...) and a dummy CA distinguished name for the corresponding
public key and let the EE auto-issue an X.509 certificate under this CA
as a replacement of certificate self-signature.
The idea for option B) was recently submitted to the PKIX wg (see
http://www.imc.org/ietf-pkix/mail-archive/msg04498.html) and its
relevance to the draft-ietf-sip-dtls-srtp-framework (and to
draft-ietf-avt-dtls-srtp as well) was raised by one of its authors.
Hope it helps,
--
- Thierry Moreau
CONNOTECH Experts-conseils inc.
9130 Place de Montgolfier
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Canada H2M 2A1
Tel.: (514)385-5691
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