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MRL meeting logs from 2019-03-11

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---
layout: post
title: Logs for the Monero Research Lab Meeting Held on 2019-03-11
summary: Network upgrade, Point release discussions, MRL work, and miscellaneous
tags: [community, crypto, research]
author: el00ruobuob / sarang
---
# Logs
**\<sarang>** Our meeting begins presently
**\<sarang>** Let's go ahead and get started. Agenda is here: https://github.com/monero-project/meta/issues/314
**\<suraeNoether>** howdy everyone
**\<sarang>** 1. GREETINGS
**\<sarang>** hi
**\<MRL-discord> \<Isthmus>** Hello! Biking, in soon.
**\<parasew[m]>** hello!
**\<sarang>** Let's recap 2. NETWORK UPGRADE
**\<sarang>** Kudos to everyone for a successful first upgrade
**\<sarang>** I don't recall when the second was slated to occur, since block arrival was stunted
**\<sarang>** Any thoughts on the upgrade after the fact?
**\<xmrmatterbridge> \<rehrar>** Hi
**\<sarang>** I believe it was dEBRUYNE who wanted an upcoming meeting specifically to talk more deeply about the future of PoW
**\<parasew[m]>** anyone monitored the "old chain"? if there have been this large amount of asics on there, and not turned off it should be visible
**\<sarang>** I believe sgp\_ ran some blackball numbers on it
**\<sarang>** and found essentially nothing of interest
**\<sarang>** but as far as hashrate, I am not sure
**\<sgp\_>** yeah, no chain reactions so far, very few known spent outputs through reused key images
**\<sgp\_>** impact on network privacy so far is essentially 0
**\<sarang>** sgp\_: were the key image reuse numbers for only v9 and v10?
**\<sgp\_>** yes, just those two
**\<sarang>** great, thanks
**\<sarang>** Relating to this, we can also introduce 3. NEXT POINT RELEASE
**\<sarang>** Not all desired non-consensus changes made it in to this release, so Sometime Soon (tm) will be a point release
**\<sarang>** BP optimizations will be one nice addition
**\<sarang>** I would like output selection to also be included... we talked about it at length at an earlier meeting
**\<dEBRUYNE>** sarang: Correct. It's a topic with a lot of depth that requires an extensive discussion imo
**\<sarang>** suraeNoether: do you have a current recommendation for output selection?
**\<suraeNoether>** i'm running into problems testing the matching code, based on this problem too
**\<sarang>** Here is a discussion of the different algorithms: https://github.com/monero-project/meta/issues/307#issuecomment-466514757
**\<suraeNoether>** iirc the output lineup method performs quite well
**\<sarang>** I prefer it among the others that were tested
**\<sarang>** But it's a change that deserves more than two thumbs-up :)
**\<suraeNoether>** there is no optimal solution, but some solutions are better than others and the output lineup method is more reasonable than the other proposals, and i have no new proposals to make (yet)
**\<sarang>** I updated the sim code (link in agenda) to examine the output weighting in more details
**\<sarang>** Hopefully the BP optimizations are less contenious
**\<suraeNoether>** uhm i think i have one possible proposal that i want to chat about with you by side channel to hash out some details
**\<sarang>** sure
**\<sarang>** We should have a formal recommendation before whatever date is set for the point release code freeze
**\<sarang>** Anything else relating to the point upgrade that ought to be discussed?
**\<sarang>** ping moneromooo perhaps
**\<xmrmatterbridge> \<rehrar>** I just want timelines. Nothing to say on content.
**\<moneromooo>** hi
**\<moneromooo>** What's the question ? :)
**\<moneromooo>** I don't know about any date. Depends when we get all the stuff on master ready really.
**\<sarang>** Anything relating to the next point release you'd like us to discuss?
**\<moneromooo>** None that come to mind right now.
**\<sarang>** ty
**\<sarang>** In that case, let's move to 4. ROUNDTABLE
**\<sarang>** suraeNoether: care to go first?
**\<sarang>** OK, I can go first instead
**\<suraeNoether>** ok
**\<sarang>** aha, go ehead
**\<suraeNoether>** heh
**\<suraeNoether>** Well, my simulations for the matching code are to the point where i'm running a matching on some test data now to generate a confusion matrix.
**\<suraeNoether>** i'm also editing the manuscript describing the whole process
**\<suraeNoether>** one of the problems i'm running into is actually simulating our output selection in part because it's not clear which direction we are going yet
**\<suraeNoether>** and it occurred to me that this could help inform our choice of output selection by seeing if one of these possibilities makes matching easier or harder
**\<sarang>** IMO matching expect spend with proper weighting seems optimal enough from a purely timing perspective
**\<sarang>** (leaving out questions of binning etc)
**\<suraeNoether>** when i say easy or hard i don't mean in terms of time, because as we've seen matching is essentially super duper fast
**\<suraeNoether>** i mean in terms of false negative and false positive rates
**\<suraeNoether>** but you are 100% on that
**\<sarang>** aw shucks
**\<suraeNoether>** i'm working on a variety of other side things but i'm shooting for this matching paper to be complete and published some time in the next 2 months
**\<sarang>** Excellent
**\<suraeNoether>** if we get more speakers for the konferenco, then i won't be speaking, but otherwise i will probably be presenting on this at the konferenco
**\<sarang>** Neat; anything else of interest to share?
**\<suraeNoether>** that's all i have today, thanks!
**\<sarang>** Righto
**\<sarang>** I have a few things
**\<xmrmatterbridge> \<learninandlurkin>** The line up is looking great btw! Fantastic effort for a first konferenco
**\<suraeNoether>** catching up on lots of reaidng in algebraic geometry :D
**\<sarang>** First, my next FFS/CCS will be posted soon
**\<sarang>** As was discussed here, in -community, and elsewhere, the request will be for immediate payout
**\<sarang>** This means both donors and I know the actual value of the donations
**\<sarang>** Since this is a big change, any questions or comments on it?
**\<sarang>** (presumably suraeNoether will be doing the same arrangement)
**\<suraeNoether>** i'm in support of this, and i will indeed be mimicking this
**\<sarang>** Folks who do not trust us to run with the money should, of course, not donate
**\<sarang>** But my hope is that our records have shown we're good for it :D
**\<binaryFate>** happy we came to that solution eventually, hopefully will be better for your guys
**\<sarang>** Thanks to binaryFate and others for agreeing to this change
**\<binaryFate>** yes the idea is that donors being careful should discourage randomers to do the same
**\<sarang>** The CCS posting will \_very\_ clearly state the arrangement, so there is no confusion
**\<binaryFate>** If you figure out the markdown
**\<sarang>** Yes indeed
**\<moneromooo>** Technically, it's within the existing rules as stated: one milestone, which consists of "sarang starts working" :)
**\<sarang>** Second, the paper that suraeNoether and I have been collaborating with external researchers on (DLSAG et al.) is in final review now
**\<sarang>** We've been asked not to share it before it's released as a preprint, as a courtesy to all authors
**\<suraeNoether>** \*nod\*
**\<sarang>** It has some great details on useful constructions that I'm sure we'll discuss at length after the preprint goes to IACR
**\<sarang>** it'll be submitted for a conference as well
**\<sarang>** Third, I wrote up some additional tests and code for Bulletproofs MPC
**\<dEBRUYNE>** sarang: How does this work if the proposal is not fully funded yet when your period starts?
**\<sarang>** Two options: either the bulk is paid out and it stays open until filled
**\<sarang>** or it all sits there until fully funded
**\<sarang>** I prefer the first, but am open to discussion
**\<sarang>** Regarding Bulletproofs MPC, real\_or\_random had some great thoughts on this before the meeting (but I won't put him on the spot)
**\<suraeNoether>** i imagine that the important part is laying out which way it goes in the proposal
**\<sarang>** the question has to do with what a malicious player can do
**\<sarang>** We chatted about the fact that an evil player could try to pull what amounts to a cancellation of partial proof elements, effectively setting the inputs to the hash that generates a F-S challenge
**\<sarang>** I couldn't find a way that this could be used as an exploit, aside from obviously generated an invalid proof
**\<sarang>** but the security proofs for BPs do require that F-S challenges are uniform
**\<sarang>** I had neglected that point when I had thought about this earlier
**\<sarang>** My strong suspicion is that proof elements are still uniformly distributed in the presence of a dishonest challenge due to the prover's randomness, and that you still get zk in this case (but not provably)
**\<sarang>** Moral: if we do anything in the future that requires/desires this scheme, these things would need to be considered
**\<sarang>** Any questions/comments relating to this?
**\<sarang>** allrightythen
**\<suraeNoether>** i think we should continue to ponder it and write something up formally about the BP MPC schemes
**\<sarang>** Well that's the thing... there's really nothing to write formally
**\<sarang>** You can probably solve all the theoretical woes by having all players commit to their proof elements before multicasting them
**\<sarang>** then an honest prover is guaranteed uniform F-S challenges
**\<xmrmatterbridge> \<learninandlurkin>** Sorry but I'm a little out of the loop here. What exactly are BP MPC for? something to do with multisig with BP?
**\<suraeNoether>** it's nice to think about collectively computing BP range proofs, but I'm still v curious about the coinjoin approach that we are considering on the larger scale.
**\<sarang>** Ideally, untrusted parties could generate single BPs for outputs
**\<suraeNoether>** after all, it's hard to even think about threat models unless we know how these things will be used in practice
**\<sarang>** Sure, this is all pie-in-the-sky right now
**\<suraeNoether>** learninandlurkin: collaborating with friends to compute a range proof for a coinjoin style transaction, so that the participants don't reveal their amounts to each other
**\<sarang>** But yes, the threat model would be very different depending on how the rounds go
**\<sarang>** Finally, suraeNoether had shown me this a while back: https://lelantus.io/lelantus.pdf
**\<suraeNoether>** agreed on the commit-and-reveal; expensive but usually does the trick to ensure participants can't be rewound inappropriately
**\<sarang>** An interesting application of some of the fundamentals behind Bulletproofs and the old StringCT scheme
**\<xmrmatterbridge> \<learninandlurkin>** So... allowing multi-input transactions where each user doesn't know the amounts of the other inputs? Sounds useful
**\<suraeNoether>** learninandlurkin hence our interest in nailing down threat models \*nod\*
**\<sarang>** I've been playing around with some of the math in that paper to see what nuggets could be extracted
**\<suraeNoether>** oh i had a brief thing to point out: isthmus and n3ptune at noncesense-research-lab answered one of my requests and we now have a complete empirical distribution of number of inputs and outputs per transaction
**\<suraeNoether>** forgot to mention this:
**\<sarang>** Neato, where is this distribution to be found?
**\<suraeNoether>** https://github.com/noncesense-research-lab/tx\_in\_out\_distribution
**\<suraeNoether>** the data surprised me
**\<dEBRUYNE> \<sarang>** I prefer the first, but am open to discussion <= I'd be OK with the first, but perhaps it would be most convenient to use a rounded number
**\<dEBRUYNE>** e.g. if 211 XMR is funded, pay out 200
**\<sarang>** You won't believe what's in tx\_distribution\_in.csv!
**\<dEBRUYNE>** Mebbe malware
**\<dEBRUYNE>** :P
**\<suraeNoether>** super heavy tails for one thing, and a rootkit for another
**\<sarang>** dEBRUYNE: perhaps a full payout at date X, and then a second payout at either date Y or completion, whichever comes first
**\<binaryFate> \<sarang>** I prefer the first, but am open to discussion <-- donors will have no incentive to fund in time, it will drag till the end of the period
**\<sarang>** binaryFate: how would you do it?
**\<binaryFate>** I like the incentive to donors of you proposing something and getting to work on it only if funded
**\<xmrmatterbridge> \<learninandlurkin>** I imagine coinjoining going on would really complicate output selection. Or is there some idea where they work off each other to get rid of heuristics?
**\<sarang>** Depends on how timely it is
**\<suraeNoether>** learningandlurkin coinjoin brings a whole new nightmare to the party. does everyone bring their own mix-ins? certainly nothing is to stop a malicious party from coinjoining with a bunch of badly selected mix-ins
**\<moneromooo>** A ring is one person only. Fake output selection is untouched.
**\<sarang>** Well each input signs with its own ring
**\<sarang>** ^
**\<moneromooo>** That person makes their own ring, yes. Otherwise others would know which is the real out.
**\<sarang>** The benefit is breaking the assumption of one-party control of outputs and the link to the input rings
**\<binaryFate>** What about simple attack of using the same 10 decoys as one of the other participants?
**\<suraeNoether>** ^
**\<msvb-mob>** Is parasew, nevvton, or txmr in the channel?
**\<binaryFate>** mmm you don't know which are decoys, nevermind ^^
**\<sarang>** If this moves forward, hopefully we can determine the necessary practical security for BPs
**\<sarang>** If we can't aggregate, they'd have to be separate for each output
**\<suraeNoether>** my beard is getting very thoroughly stroked this morning. much to think about...
**\<sarang>** I believe we'd get practical security without player commitments, but not provable
**\<sarang>** Anyway: does anyone else wish to share interesting research before we close?
**\<xmrmatterbridge> \<learninandlurkin>** Yes it sounds like the interplay between coinjoin and ringsigs will require some diagrams for me to ever understand. Could get complicated.
**\<suraeNoether>** i think you would want a commit-and-reveal stage for everyone to see the ring members to prevent malicious ring intersection in the coinjoin
**\<sarang>** MoneroCoinJoin: an easy 14-round process!
**\<suraeNoether>** isthmus and i have been chatting about methods of extracting the true spend-time distribution from the monero blockchain without knowing exactly which outputs have been spent
**\<suraeNoether>** that's a very nascent conversation, though I think it'll end up being a very straightforward project
**\<sarang>** Discussions in #noncesense-research-lab I presume?
**\<xmrmatterbridge> \<learninandlurkin>** so, truish spend-time distribution
**\<binaryFate>** Are there regular meetings on this or just continuous discussion? I had been working on this at some point and have some code around aiming to graphically show the real spend distribution
**\<sarang>** I've seen a few informal conversations in #noncesense-research-lab but didn't know if suraeNoether had something more formal
**\<suraeNoether>** binaryFate: ah, no, this has been a casual conversation by side channel, but there is clearly interest
**\<suraeNoether>** i'll start blabbing about it in here more publicly
**\<sarang>** In the interest of time, let's review 6. ACTION ITEMS and then close to continue discussion afterword
**\<binaryFate>** Ok don't hesitate to ping me on this
**\<sarang>** I will be posting my CCS request soon, tidying up the output selection stuff for a recommendation, getting the DLSAG application paper reviewed and out the door, and playing around with that Lelantus paper when/if I get a chance
**\<sarang>** suraeNoether: ?
**\<suraeNoether>** CCS request, working on simulations and measurable numbers for matching, and looking into using our matching code to answer questions about output selection
**\<sarang>** excellent
**\<suraeNoether>** also casual github maintenance
**\<sarang>** Any final questions or remarks before we adjourn?
**\<xmrmatterbridge> \<learninandlurkin>** once you guys have made a recommendation for output selection
**\<xmrmatterbridge> \<learninandlurkin>** and it gets implemented, what's the next big focus?
**\<sarang>** There will be much to consider in the realm of refund and payment channels
**\<xmrmatterbridge> \<learninandlurkin>** Ooh yes the refund ideas from a while back were really interesting
**\<sarang>** and some aspects of output selection, like linking spends across rings in txns, is not solved yet
**\<xmrmatterbridge> \<learninandlurkin>** Seems like a logical next area of research
**\<sarang>** and if coinjoin works out, there will be a lot to consider with that
**\<sarang>** Also transaction relay and network-level anonymity stuff that's still in progress
**\<sarang>** To quote the Simpsons: "like the cleaning of a house... IT NEVER ENDS"
**\<sarang>** But on that note, our meeting does end
**\<sarang>** Thanks to everyone for attending. We're adjourned; let the conversations continue