Published on March 4, 2014
SIP and DNS-sec based TLS setup (DANE) random thoughts by firstname.lastname@example.org
Olle E. Johansson ! V 3.14 - 2014-02-27 IETF 89, London, March 2014 1
Today’s question • SIP & DANE Do we want to add this work to our charter? 2 Olle E. Johansson
SIP & TLS • SIP uri target domain is veriﬁed against SubjectAltName uri records • if no SAN uri records, SAN DNS records • If no SAN records, CN • But no CN check if there are SAN records! RFC 5922 SIP & DANE 3 Olle E. Johansson
Dependencies DNS TLS SIP SIP domain certiﬁcates DNSsec DANE SIP + DANE To trust DANE you need to trust DNSsec SIP & DANE 4
Dane simpliﬁed DNS zone signed, trusted TLS server stockholm.example.com Certiﬁcate identiﬁer TLS client SIP & DANE 5
Questions TLS server stockholm.example.com Is the certiﬁcate signer (CA) the right one? Do I trust this certiﬁcate? Am I talking with the right server? TLS client SIP & DANE 6
DANE simpliﬁed TLS server My service use this CA DNS zone signed, trusted stockholm.example.com My service use this certiﬁcate TLS client SIP & DANE My service use the private key that match this public key 7 Certiﬁcate identiﬁer
Dane summary • • • SIP & DANE Can publish constraints • • This CA is the only one accepted This certiﬁcate is the only one accepted Can publish root of private CA • This CA cert is the one used to sign my server certiﬁcates Can publish certiﬁcates In all cases, a full cert or the public key can be published - or ﬁngerprints of these. 8 Olle E. Johansson
TLSA selector and matching Selector • 0 - Full certiﬁcate included in TLSA • 1 - Public key included in TLSA Matching • 0 = Exact match • 1 = the data is SHA-256 hash of content • 2 = the data is SHA-512 hash of content SIP & DANE 9 Olle E. Johansson
TLSA records • Usage 0: CA constraint. Certiﬁcate or public key of CA • Usage 1: Certiﬁcate constraint. Certiﬁcate or public key of cert signed by CA. • Usage 2. Certiﬁcate or public key of cert serving as trust anchor for the cert given by the server (”private CA”) • Usage 3: A certiﬁcate or public key that matches the cert given by the server (No PKIX check) SIP & DANE 10 Olle E. Johansson
DANE simpliﬁed DNS zone signed, trusted TLS server stockholm.example.com 2.Verify the TLS server cert in handshake with TLSA record. TLS client SIP & DANE 1. Check the TLSA record for service 11 Certiﬁcate identiﬁer
The DANE promise • If you trust the DNS (using DNSsec) then we can use that instead of the certiﬁcate store to check server identity and authorisation. SIP & DANE 12 Olle E. Johansson
Back to SIP SIP & DANE 13
SIP DOMAIN CERTS • Connect a SIP URI domain part with a certiﬁcate • Mix server identiﬁcation with domain authorisation • Only domains in the certiﬁcates • New certiﬁcate every time we add a domain or subdomain • No wildcard certs SIP & DANE 14 Olle E. Johansson
What about SNI • Many certiﬁcates on one TLS server and IP. • No support for DNS names • ONLY host names. SIP & DANE 15 Olle E. Johansson
SIP sip:email@example.com example.com NAPTR We just trust that we’ve hit the right server if the cert contains the domain. example.net SRV host sip02.example.org Cert with “example.com” SIP & DANE 16 Olle E. Johansson
DANE Secure delegation sip:firstname.lastname@example.org if the DNS queries for NAPTR and SRV records was veriﬁed and protected with DNSsec, we have a secure delegation from example.com to sip02.example.org Protected by DNSsec example.com NAPTR example.net SRV host sip02.example.org Cert with “sip02.example.org” SIP & DANE 17 Olle E. Johansson
Not fully secure is insecure • If the NAPTR was DNSsec protected but not the SRV, we have no secure delegation. • If there’s no DNSsec in either NAPTR nor SRV we’re insecure too. • The SIP Uri to TLS certiﬁcate matching in RFC 5922 applies in this case SIP & DANE 18 Olle E. Johansson
If we have a secure delegation • Check for TLSA record for the srv host name and port • _5068._udp.sip02.example.org • If no TLSA record is found, then DANE doesn’t apply - proceed according to RFC 5922 • If TLSA record exists, continue to the next slide SIP & DANE 19 Olle E. Johansson
Our identiﬁers • The SIP domain in the request URI • Used in insecure delegation • The SRV FQDN from SRV lookup of the domain (protected with DNSsec) • Used in secure delegation as well as with TLSA record veriﬁcation SIP & DANE 20 Olle E. Johansson
Validation • With TLSA usage 0 and 1, use these constraints then verify cert as before • With TLSA usage 2 and 3, use the information to validate cert • • SIP & DANE If either TLSA validation fails, connection should fail. With usage 0 and 1, after TLSA validation normal PKIX validation happens. 21 Olle E. Johansson
Sideways jumps • When a NAPTR or SRV record points to a name in another domain, the client needs to make sure that the new domain is validated in DNSsec as well. • If not, delegation is insecure SIP & DANE 22 Olle E. Johansson
SIP Fallback logic • If there’s no secure delegation, use RFC 5922, if that fails go to next SRV server in the list • When out of SRV servers, TLS connection has failed. SIP & DANE 23 Olle E. Johansson
Compatibility with nonSRV clients • Fallback to RFC 5922 • Since dane-srv-02 requires TLS SNI this will be sorted out by the server. • SRV/DANE compatible UAs will require cert for SRV host name • Non SRV/DANE UAs will require cert with SIP uri target domain SIP & DANE 24 Olle E. Johansson
If no SNI support is available • Cert with • CommonName = hostname • SubjectAltName = SIP domain SIP & DANE 25 Olle E. Johansson
SIP connection reuse • RFC 5923 use TLS cert content to add aliases to a connection. • With DANE, the cert will include only the hostname • SIP/DANE will have to add aliases as they are veriﬁed using DNSsec • If a domain share a SRV hostname and the trust chain is veriﬁed between domain and SRV, the existing connection to the SRV host may be used for this domain too (and alias added to the alias table) SIP & DANE 26 Olle E. Johansson
Veriﬁcation of client certiﬁcates in RFC 5923 • Connection reuse requires a SIP server using RFC 5923 to request a client certiﬁcate • Which DNS name do we use to look up TLSA records and verify the client? Can this be done? SIP & DANE 27 Olle E. Johansson
Not to worry about now • SIP identity • SIMPLE • SIPS: uri’s For these use cases, there’s no difference compared with other TLS usage in SIP. SIP & DANE 28 Olle E. Johansson
Reading material RFC 5922 SIP Domain Certiﬁcates RFC 6698 draft-ietf-dane-srv DNS based authentication of named entities (DANE) DANE and SRV/MX records draft-ietf-dane-smime DANE and SMIME identities draft-ogud-dane-vocabulary DANE vocabulary for application usages RFC 5923 Connection Reuse in SIP draft-johansson-dispatch-dane-sip-01 The draft on SIP and DANE SIP & DANE 29 Olle E. Johansson
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