Subject: [stir] Notes from lunch meeting around reducing spam

From: Cullen Jennings <[email-masked]>
Date: Thu, 22 Mar 2018 16:40:43 +0000

Huge thanks to Mat Miller for taking notes. 

SIPCOIN/CALLBACK Side Meeting

* Hilton Meeting Rooms 1-4
* 2018-03-22 T 12:15:00

 We had 16 people. 

======== SIPCOIN ========
DISCLOSURES

* There is IPR on SIPCoin draft, will be posted
* other prior art (hashcash, for email then phone)
  - The compute time is too long for typical use

OVERVIEW

* mint a coin ahead of time
* burn a coin at use
* posted to a CA for verification by signing block
* merkle tree to track history efficiently

IETF responsible for determining value
- WG? document?
- robocallers packing the WG?
- not possible/feasible for such an org

COMPUTE

* bitcoin is competitive mining
* assumption is robocalls will use most optimal equip (ASICs)
* less compute --> less coins
* going with "unresistant" models that favor ASICs is ok
  - ASICs needed for buy-in
  - (ots ASCIs, cloud service in Iceland, etc)

BREAKING IT

* centralized email spam mitigations <-- more centralized services
  - email spammers: central advertiser contracts with smaller ops, who contracts with smaller ops et al .... who operates botnets
  - small players see bits, and money filters down

ALTERNATIVES

The idea is make the problem an economics one
* SIPCoin is one
* donations to LE or other foundations

rather than community-based, make it regulatory
  - pay penalties if you're not doing STIR
  - big carriers cannot legally force downstream to comply (needs to be regulators)

if PASSPOrT goes to edges, then leave it to ends to force compliance laws cannot:
* bond on the phone number holder
* who will issue the bond? (financial incentives?)
  - carrier bonding --> deal with legal but incentivized?
  - ends bonding --> not sure

* problem starts to mitigates with verified source (STIR)
  - PSTN is the biggest problem
  - SIP has more leverage

* traceability works for post-facto (forensics), but not real-time
  - may only work for robocalls if high value victim (e.g., Senator) 

* total solution involves multiple factors (relevance scores)
  - find the knobs to turn the costs up for spammers

CHALLENGES

* cost on acquiring numbers vs impersonation
* cheap/free gateways also complicate (e.g, Skype, Twilio, Tropo, etc)
  - banks of numbers --> spammers mixed into legitimate callers

* phone calling margins are tightening (??)
* all carriers have to offer call blocking services (via FCC)
  - Opt-in, centralized SIP app analyzing
  - works really well
  - e.g., COMCAST -- NoMoRobo
  - carrier cost is very very low (so far)
  - still based on unverified reported numbers (spammers can adapt)
* honeypots and heuristics interesting
  - could be an economic disincentive 

FOLLOW UPS

* FCC motivated for solutions
* research validation
  - Barbara van Schewick
  - Moz Foundation for more contacts

* Mark and Jon to help continue it
* how to bootstrap?

======== CALLBACK ========

OVERVIEW
* callee calls back the caller (no dial)
  - verify the callers really made the call

* each agent builds up cache of certs found

QUESTIONS

ASSUMPTION

* validation on cert (by accepted CA), not on the identity per-se

CHALLENGES

* if the middle is not SIP (e.g., SS7)
  - OOB is solving this (designed for smart end-points)
  - might also trickle into SHAKEN
  - OOB still assumes 8226 cert

* More work on the gateways (SIP terminations)
  - put something in front-end to do this
  - also not yet doing STIR (?)
  - out-of-band made for this issue

* deployment ()?
  - STIR is a set of tools
  - work in ACME to define proofs et al (for PASSPOrT)
  - to start, agreement on what the CAs are
  - this will get shaken out over the next year or so
  
FOLLOW UPS

* look for a distributed technique to generate certs that are combined over the top?