OpenSIPit 2021 Notes¶

Stir/Shaken¶

George's Notes:¶

• We need to convert over to X509 certificates instead of EC certificates.
• We need to send the "dest->tn" object in our Identity header.
• We need to send a SIP "Date" header. Example from Liviu:
  • Wed, 14 Apr 2021 13:17:35 GMT
• We're not filtering bad certificate URLs. The SipVicious guys were able to send a "file:///dev/random" URL which put Asterisk into a spin loop reading random data and writing it to /var/lib/asterisk/keys/stir_shaken/random.
• We need to clarify and document the 3 types of certificate expiration...
  • We compare the current time to the timestamp sent in the Identity header and reject if there's more than signature_timeout seconds difference.
  • When we retrieve the certificate using the URL in the Identity header, we compare the HTTP "Cache-Control" "max-age" parameter or the Expires header to the time we cached the certificate the last time we retrieved it.
  • OpenSSL looks at the certificate valid date range.
• Right now we fail if there's no "Cache-Control" or "Expires" header in the HTTP response we reject. That's not good.
• We're using Base64 to encode and decode stuff and we should be using Base64URL instead.
• We should be using randomly generated UUID for every request's orgid
• We're saving certs in /var/lib/asterisk/keys/stir_shaken with the same name as in the URL. For instance: http://asterisk.opensipit.net/cert.pem is saved as /var/lib/asterisk/keys/stir_shaken/cert.pem. If another request comes in like http://opensips.opensipit.net/cert.pem,(http://opensips.opensipit.net/cert.pem-) we overwrite Asterisk's cert.pem. We need to save the cert using the cert's serial number rather than its file name.
• There are some error situations where the RFC says we MUST return a certain response code but we're leaving it to the dialplan author to check and reject and there's currently no way for the dialplan author to send specific SIP response codes. I suggest we do 2 things...
  • Create a pjsip dialplan function that can set a specific SIP response code for Hangup() to use.
  • Split the stir_shaken endpoint option to 2 options...
    • stir_shaken_attest = (yes | no) to control whether we send an Identity header or not
    • stir_shaken_verify = ( no | permissive | enforce ) where permissive would be the behavior we have today where we leave handling the verification result it up to the dialplan author and where enforcing makes res_pjsip_stir_shaken automatically send back the correct response code on failure.
• We need enhance the STIR_SHAKEN dialplan function to add a verify_result_code code to get a numeric verification result code instead of the text result message.
• We need to update the documentation for the STIR_SHAKEN function to include the possible result codes and messages.
• When Asterisk is compiled with TEST_FRAMEWORK res_pjsip_stir_shaken doesn't do the check for the timestamp in the Identity header. It should.

Andreas Granig has a GitHub repo with a ton of Stir/Shaken sipp tests... https://github.com/agranig/stirshaken-scenarios It currently relies on a patched version of sipp (provided in the repo) but he's working to get the changes merged upstream. If anything, it's a good reference for what we should test ourselves.

RFC8760¶

George's Notes:¶

• Eventually we (and pjproject) need to support the additional authentication digest algorithms defined in RFC8760 which include SHA-256 and SHA512-256.
• We are not currently tolerant of RFC8760 compliant UASs that send us multiple WWW-Authenticate headers. If they send us one using SHA-256 and a second one using MD5, we fail when we see SHA-256 and don't continue to look for more WWW-Authenticate headers. I have a patch that at least makes us tolerant.