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Last Notes

2023-06-08 00:52:05 CEST

- reply

📅 Original date posted:2021-04-24
📝 Original message:ACK adding Kalle
On Fri, Apr 23, 2021 at 5:51 PM Antoine Riard via bitcoin-dev <
bitcoin-dev at lists.linuxfoundation.org> wrote:
> Hi Luke,
>
> For the records and the subscribers of this list not following
> #bitcoin-core-dev, this mail follows a discussion which did happen during
> yesterday irc meetings.
> Logs here : http://gnusha.org/bitcoin-core-dev/2021-04-22.log
>
> I'll reiterate my opinion expressed during the meeting. If this proposal
> to extend the bip editorship membership doesn't satisfy parties involved or
> anyone in the community, I'm strongly opposed to have the matter sliced by
> admins of the Bitcoin github org. I believe that defect or uncertainty in
> the BIP Process shouldn't be solved by GH janitorial roles and I think
> their roles don't bestow to intervene in case of loopholes. Further, you
> have far more contributors involved in the BIP Process rather than only
> Bitcoin Core ones. FWIW, such precedent merits would be quite similar to
> lobby directly GH staff...
>
> Unless we harm Bitcoin users by not acting, I think we should always be
> respectful of procedural forms. And in the lack of such forms, stay patient
> until a solution satisfy everyone.
>
> I would recommend the BIP editorship, once extended or not, to move in its
> own repository in the future.
>
> Cheers,
> Antoine
>
>
>
>
> Le jeu. 22 avr. 2021 à 22:09, Luke Dashjr via bitcoin-dev <
> bitcoin-dev at lists.linuxfoundation.org> a écrit :
>
>> Unless there are objections, I intend to add Kalle Alm as a BIP editor to
>> assist in merging PRs into the bips git repo.
>>
>> Since there is no explicit process to adding BIP editors, IMO it should
>> be
>> fine to use BIP 2's Process BIP progression:
>>
>> > A process BIP may change status from Draft to Active when it achieves
>> > rough consensus on the mailing list. Such a proposal is said to have
>> > rough consensus if it has been open to discussion on the development
>> > mailing list for at least one month, and no person maintains any
>> > unaddressed substantiated objections to it.
>>
>> A Process BIP could be opened for each new editor, but IMO that is
>> unnecessary. If anyone feels there is a need for a new Process BIP, we
>> can go
>> that route, but there is prior precedent for BIP editors appointing new
>> BIP
>> editors, so I think this should be fine.
>>
>> Please speak up soon if you disagree.
>>
>> Luke
>> _______________________________________________
>> bitcoin-dev mailing list
>> bitcoin-dev at lists.linuxfoundation.org
>> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>>
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev at lists.linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>
--
Best,
Ádám
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2023-06-07 20:26:55 CEST

- reply

📅 Original date posted:2020-09-19
📝 Original message:Wouldn't this enable a passive adversary listening the mempool to associate
unrelated TXO clusters to the same user?
On Sat, Sep 19, 2020, 15:38 David A. Harding via bitcoin-dev <
bitcoin-dev at lists.linuxfoundation.org> wrote:
> On Fri, Sep 18, 2020 at 05:51:39PM -0700, Jeremy via bitcoin-dev wrote:
> > I'd like to share with you a draft proposal for a mechanism to replace
> > CPFP and RBF for increasing fees on transactions in the mempool that
> > should be more robust against attacks.
>
> Interesting idea! This is going to take a while to think about, but I
> have one immediate question:
>
> > To prevent garbage sponsors, we also require that:
> >
> > 1. The Sponsor's feerate must be greater than the Sponsored's ancestor
> fee rate
> >
> > We allow one Sponsor to replace another subject to normal replacement
> > policies, they are treated as conflicts.
>
> Is this in the reference implementation? I don't see it and I'm
> confused by this text. I think it could mean either:
>
> 1. Sponsor Tx A can be replaced by Sponsor Tx B if A and B have at least
> one input in common (which is part of the "normal replacement policies")
>
> 2. A can be replaced by B even if they don't have any inputs in common
> as long as they do have a Sponsor Vector in common (while otherwise
> using the "normal replacement policies").
>
> In the first case, I think Mallory can prevent Bob from
> sponsor-fee-bumping (sponsor-bumping?) his transaction by submitting a
> sponsor before he does; since Bob has no control over Mallory's inputs,
> he can't replace Mallory's sponsor tx.
>
> In the second case, I think Mallory can use an existing pinning
> technique to make it expensive for Bob to fee bump. The normal
> replacement policies require a replacement to pay an absolute higher fee
> than the original transaction, so Mallory can create a 100,000 vbyte
> transaction with a single-vector sponsor at the end pointing to Bob's
> transaction. This sponsor transaction pays the same feerate as Bob's
> transaction---let's say 50 nBTC/vbyte, so 5 mBTC total fee. In order
> for Bob to replace Mallory's sponsor transaction with his own sponsor
> transaction, Bob needs to pay the incremental relay feerate (10
> nBTC/vbyte) more, so 6 mBTC total ($66 at $11k/BTC).
>
> Thanks,
>
> -Dave
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev at lists.linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>
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2023-06-07 20:23:00 CEST

- reply

📅 Original date posted:2020-02-22
📝 Original message:> It seems to me that most users will not have nearly the same output of
"around 1 BTC"
While that would be true out of context, it depends on how you interpret it
and they interpret it really broadly: " One input might be 0.03771049 BCH;
the next might be 0.24881232 BCH, etc. "
> anyway if you deploy this on a real live mainnet, and if your math
requires that you have "around 1 BTC" outputs per user. you might as well
just use equal-valued CoinJoins, where the equal-valued outputs at least
are completely unlinked from the inputs.
> e.g. if you have a CashFusion transaction with outputs 1.0, 1.1, 0.99,
you could transform that to a CoinJoin with 0.99, 0.99, 0.99, 0.01, 0.11
outputs.
Equal valued coinjoins (1) waste more blockspace as your example
illustrates and (2) prevent arbitrary amounts, so you cannot send in
coinjoins.
> Indeed, the change outputs of an equal-valued CoinJoin would have similar
analyses to CashFusion, since the same analysis "around 1 BTC" can be
performed with the CoinJoin change outputs "around 0 BTC".
I've been wondering about this too. I think it cannot be applied to
existing CoinJoin schemes, as coin selection heuristics are quite a help
and that could be a reason why the changes can be deanonymized (I assume.)
For example if I want to analyze a Wasabi CJ, then I assume every input
that have > 0.1 BTC value to be THE valid input partition and I will only
look for the valid matching partition on the output side. I won't try to
find all the partitions and look at all the possible subset sums. (
https://github.com/nopara73/Notes/blob/master/BellNumber.md,
https://github.com/nopara73/Notes/blob/master/SubSetSum.md)
At the very least coin selection for equal value coinjoins can be relaxed
to remove such assumptions and make the above math applicable for the
change. (If works.)
On Sun, Dec 29, 2019 at 12:25 AM ZmnSCPxj <ZmnSCPxj at protonmail.com> wrote:
> Good morning Adam,
>
> > The CashFusion research came out of the Bitcoin Cash camp, thus this
> probably went under the radar of many of you. I would like to ask your
> opinions on the research's claim that, if non-equal value coinjoins can be
> really relied on for privacy or not.
> >
> > (Btw, there were also similar ideas in the Knapsack paper in 2017:
> https://www.comsys.rwth-aachen.de/fileadmin/papers/2017/2017-maurer-trustcom-coinjoin.pdf
> )
> >
> >
> https://github.com/cashshuffle/spec/blob/master/CASHFUSION.md#avoiding-amount-linkages-through-combinatorics
>
> >
> > I copy the most relevant paragraphs here:
> >
> > ---------BEGIN QUOTE ---------
> >
> >
> > Consider a transaction where 10 people have each brought 10 inputs of
> arbitary amounts in the neighborhood of ~0.1 BCH. One input might be
> 0.03771049 BCH; the next might be 0.24881232 BCH, etc. All parties have
> chosen to consolidate their coins, so the transaction has 10 outputs of
> around 1 BCH. So the transaction has 100 inputs, and 10 outputs. The first
> output might be 0.91128495, the next could be 1.79783710, etc.
> >
> > Now, there are 100!/(10!)^10 ~= 10^92 ways to partition the inputs into
> a list of 10 sets of 10 inputs, but only a tiny fraction of these
> partitions will produce the precise output list. So, how many ways produce
> this exact output list? We can estimate with some napkin math. First,
> recognize that for each partitioning, each output will typically land in a
> range of ~10^8 discrete possibilities (around 1 BCH wide, with a 0.00000001
> BCH resolution). The first 9 outputs all have this range of possibilities,
> and the last will be constrained by the others. So, the 10^92 possibilies
> will land somewhere within a 9-dimensional grid that cointains
> (10^8)^9=10^72 possible distinct sites, one site which is our actual output
> list. Since we are stuffing 10^92 possibilties into a grid that contains
> only 10^72 sites, then this means on average, each site will have 10^20
> possibilities.
> >
> > Based on the example above, we can see that not only are there a huge
> number of partitions, but that even with a fast algorithm that could find
> matching partitions, it would produce around 10^20 possible valid
> configurations. With 10^20 possibilities, there is essentially no linkage.
> The Cash Fusion scheme actually extends this obfuscation even further. Not
> only can players bring many inputs, they can also have multiple outputs.
> >
> > ---------END QUOTE ---------
> > --
>
>
> It seems to me that most users will not have nearly the same output of
> "around 1 BTC" anyway if you deploy this on a real live mainnet, and if
> your math requires that you have "around 1 BTC" outputs per user. you might
> as well just use equal-valued CoinJoins, where the equal-valued outputs at
> least are completely unlinked from the inputs.
>
> Indeed, the change outputs of an equal-valued CoinJoin would have similar
> analyses to CashFusion, since the same analysis "around 1 BTC" can be
> performed with the CoinJoin change outputs "around 0 BTC".
>
> * You can always transform a CashFusion transaction whose outputs are
> "around 1 BTC" to a CoinJoin transaction with equal-valued outputs and some
> change outputs, with the equal-valued outputs having equal value to the
> smallest CashFusion output.
> * e.g. if you have a CashFusion transaction with outputs 1.0, 1.1, 0.99,
> you could transform that to a CoinJoin with 0.99, 0.99, 0.99, 0.01, 0.11
> outputs.
> * Conversely, you can transform an equal-valued CoinJoin transaction to a
> CashFusion transaction using the same technique.
> * That implies that the change outputs of an equal-valued CoinJoin have
> the same linkability as the outputs of the equivalent CashFusion
> transaction.
> * At least with equal-valued CoinJoin, the equal-valued outputs have 0
> linkability with inputs (at least with only that transaction in isolation).
> The same cannot be said of CashFusion, because the value involved is
> just in a single UTXO.
>
> Regards,
> ZmnSCPxj
>
--
Best,
Ádám
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2023-06-07 20:22:09 CEST

- reply

📅 Original date posted:2019-12-27
📝 Original message:The CashFusion research came out of the Bitcoin Cash camp, thus this
probably went under the radar of many of you. I would like to ask your
opinions on the research's claim that, if non-equal value coinjoins can be
really relied on for privacy or not.
(Btw, there were also similar ideas in the Knapsack paper in 2017:
https://www.comsys.rwth-aachen.de/fileadmin/papers/2017/2017-maurer-trustcom-coinjoin.pdf
)
https://github.com/cashshuffle/spec/blob/master/CASHFUSION.md#avoiding-amount-linkages-through-combinatorics
I copy the most relevant paragraphs here:
---------BEGIN QUOTE ---------
Consider a transaction where 10 people have each brought 10 inputs of
arbitary amounts in the neighborhood of ~0.1 BCH. One input might be
0.03771049 BCH; the next might be 0.24881232 BCH, etc. All parties have
chosen to consolidate their coins, so the transaction has 10 outputs of
around 1 BCH. So the transaction has 100 inputs, and 10 outputs. The first
output might be 0.91128495, the next could be 1.79783710, etc.
Now, there are 100!/(10!)^10 ~= 10^92 ways to partition the inputs into a
list of 10 sets of 10 inputs, but only a tiny fraction of these partitions
will produce the precise output list. So, how many ways produce this exact
output list? We can estimate with some napkin math. First, recognize that
for each partitioning, each output will typically land in a range of ~10^8
discrete possibilities (around 1 BCH wide, with a 0.00000001 BCH
resolution). The first 9 outputs all have this range of possibilities, and
the last will be constrained by the others. So, the 10^92 possibilies will
land somewhere within a 9-dimensional grid that cointains (10^8)^9=10^72
possible distinct sites, one site which is our actual output list. Since we
are stuffing 10^92 possibilties into a grid that contains only 10^72 sites,
then this means on average, each site will have 10^20 possibilities.
Based on the example above, we can see that not only are there a huge
number of partitions, but that even with a fast algorithm that could find
matching partitions, it would produce around 10^20 possible valid
configurations. With 10^20 possibilities, there is essentially no linkage.
The Cash Fusion scheme actually extends this obfuscation even further. Not
only can players bring many inputs, they can also have multiple outputs.
---------END QUOTE ---------
--
Best,
Ádám
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2023-06-07 20:20:41 CEST

- reply

📅 Original date posted:2019-09-23
📝 Original message:Please also take a look at "Applying Private Information Retrieval to
Lightweight Bitcoin Clients" Scaling Bitcoin talk. The academics were not
aware of BIP158 at all, yet came up with a similar scheme independently.
On Sat, Sep 21, 2019 at 11:40 PM Tamas Blummer via bitcoin-dev <
bitcoin-dev at lists.linuxfoundation.org> wrote:
> Hi Aleksey,
>
> Yes, BIP158 uses the block hash to seed the hash function, which makes
> distinct block filters non-aggregatable
> for common values. Aggregate fiters on ranges of blocks would have to use
> some other seed and then
> achive significant savings using the same design.
>
> I think that the most likely use of filters is to decide if a newly
> announced block should be downloaded and
> not scanning over the entire chain, where aggregate filters would help. I
> also suspect that whole chain
> scans would be better served with plain sequential reads in map-reduce
> style.
>
> Typical clients do not care of filters for blocks before the birth date of
> their wallet’s keys, so they skip over the
> majority of history which is a bigger saving than any aggregate filter.
>
> I wish we get a filter committed as commitment would unlock more utility
> than any marginal savings through
> more elaborate design.
>
> Tamas Blummer
>
> On Sep 19, 2019, at 19:20, admin--- via bitcoin-dev <
> bitcoin-dev at lists.linuxfoundation.org> wrote:
>
> Hello list,
>
> Here is a link for a draft of a BIP for compact probabilistic block
> filters alternative of BIP 158
>
>
> https://docs.google.com/document/d/1jH9tEUyb9w2OZd4-kxfGuyNIIZzmgkEb_z0qSxv80ik/edit?usp=sharing
>
> Summary:
>
> - BIP 158 false positive rate is low, we can achieve lower bandwidth
> with higher false positive rate filter while sync blockchain
>
> - BIP 158 not do not support filter batching by design of used parameters
> for siphash and Golomb coding optimal parameters
>
> - Alternative compression with delta coding and splitting data to 2 bit
> string sequences. First for data without prefixes, second one for
> information about bit length written to first sequence.
> Second sequence have a lot of duplicates, compressed with 2 round of
> Huffman algorithm. (Effectivity about 98% vs Golomb with optimal parameters)
>
> - Block filters batching reduce filter size significantly
>
> - Separation of filters by address type allows lite client not to download
> redundant information without compromising privacy.
>
> - Lite client filters download strategy: get biggest filter (smallest
> blocks/size rate) for blocks range, in case positive test -> get medium
> filters to reduce blocks range -> get block filters for affected range ->
> download affected blocks over TOR
>
> Implementation (python):
> https://github.com/bitaps-com/pybtc/blob/bugfix/pybtc/functions/filters.py#L172
>
> Exactly information from mainnet about size for separated filters by
> address types and batch size will be added within few days.
>
> Thanks for any feedback.
> Aleksey Karpov
>
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev at lists.linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>
>
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev at lists.linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>
--
Best,
Ádám
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