[bitcoin-dev] Bitcoin dev meeting in layman's terms (2015-10-8)

[G1lius Caesar <g1liusbitcoin@gmail.com>]

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Once again my attempt to summarize and explain the weekly bitcoin developer
meeting in layman's terms.
Link to last weeks layman's summarization:
https://www.mail-archive.com/bitcoin-dev@lists.linuxfoundation.org/msg02445.html



*Disclaimer*

Please bare in mind I'm not a developer and I'd have problems coding "hello
world!", so some things might be incorrect or plain wrong.
Like any other write-up it likely contains personal biases, although I try
to stay as neutral as I can.
There are no decisions being made in these meetings, so if I say "everyone
agrees" this means everyone present in the meeting, that's not consensus,
but since a fair amount of devs are present it's a good representation.
The dev IRC and mailinglist are for bitcoin development purposes. If you
have not contributed actual code to a bitcoin-implementation, this is
probably not the place you want to reach out to. There are many places to
discuss things that the developers read, including this sub-reddit.


link to this week logs (
http://bitcoinstats.com/irc/bitcoin-dev/logs/2015/10/08#l1444330778.0 )
link to meeting minutes (
https://docs.google.com/document/d/1hCDuOBNpqrZ0NLzvgrs2kDIF3g97sOv-FyneHjQellk/edit
)


Main topics discussed this week where:

Mempool limiting: chain limits
Low-S change
CLTV & CSV review
Creation of bitcoin discuss mailing list


**off-topic but important notice**

This issue ( https://github.com/feross/buffer/pull/81 ) has made most JS
bitcoin software vulnerable to generating incorrect public keys.
"This is an ecosystem threat with the potential to cause millions of
dollars in losses that needs higher visibility; though it's not a bitcoin
core / bitcoin network issue.
Common, critical, JS code is broken that may cause the generation of
incorrect pubkeys (among other issues). Anyone who cares for a JS
implementation should read that PR."


**Mempool limiting: chain limits**

- background

(c/p from last week)
Chain in this context means connected transactions. When you send a
transaction that depends on another transaction that has yet to be
confirmed we talk about a chain of transactions.
Miners ideally take the whole chain into account instead of just every
single transaction (although that's not widely implemented afaik). So while
a single transaction might not have a sufficient fee, a depending
transaction could have a high enough fee to make it worthwhile to mine both.
This is commonly known as child-pays-for-parent.
Since you can make these chains very big it's possible to clog up the
mempool this way.
The first unconfirmed transaction is called the ancestor and the
transactions depending on it the descendants. The total amount of
transactions is reffered to as "packages".

- since last week

As said in "Chain limits" last week Morcos did write a proposal about
lowering the default limits for transaction-chains.
2 use cases came up which are currently in use or happened before:
As example: someone buys bitcoin from a website and can spend those bitcoin
in the marketplace of the same website without waiting for confirmation in
order to improve the bitcoin user-experience. This leaves a sequential
transaction chain. They don't need to chain more than 5 transactions deep
for this, and it falls within the proposed limits.
What's not within the proposed limits is the chain of +/- 100 transactions
a company had during the spam-attacks. These where simply increased
activities by end-users while not enough UTXO's where available (3 to be
precise)(UTXO: unspent transaction output, an output that can be used as
input for a new transaction).
Notably this is with the best practices of using confirmed transactions
first.
Ways this can be solved from the company's end is to have more UTXO's
available before hand, bundling transactions (which requires delaying
customer's request) or using replace-by-fee to add payees (which saves
blockchain space, is cheaper in fees and gets transactions through quicker,
but is not widely deployed by miners atm).
Bare in mind these proposals are for default values for the memorypool, not
in any way hard limits.


- meeting comments

Sense of urgency. Quoting sipa: "my mempool is 2.5G... we better get some
solution!"
Current attack analysis assumes child-pays-for-parent mining, it should
probably be done again without.
Higher limits on number of transactions increase attack-vectors.
Proposed number of transactions gets some push-back, total size limit not.
Mixing default values (for example having a 50% of a 10/10 limit and 50% of
a 100/100 limit) wastes bandwidth while there are too many factors that
limit utility of long chains as well.
25 transaction limit ought to be enough for everyone (for now).

- meeting conclusion

Review & test "Limit mempool by throwing away the cheapest txn and setting
min relay fee to it" ( https://github.com/bitcoin/bitcoin/pull/6722 )
Provide support for "Lower default limits for tx chains" (
https://github.com/bitcoin/bitcoin/pull/6771 ) aka convince people 25
should be enough.



**Low-S change**

- background

This is in regards to the recent malleability attack. Which is caused by a
value 'S' in the ECDSA signature which can be 2 values, a high and low
value and still be valid. Resulting in different transaction id's. more
info:
http://blog.coinkite.com/post/130318407326/ongoing-bitcoin-malleability-attack-low-s-high
A solution for this is to require nodes to have the "low-s" encoding for
signatures.
Downside is that it will block most transactions made by sufficiently out
of date software (+/- pre-march 2014)
This does not replace the need for BIP62, it only eliminates the cheap DOS
attack.


- meeting comments

95% of transactions already confirm to this, and more fixes have been
applied since.
BlueMatt has a node which several people are running that auto-malleates to
low-s transactions.
Questions whether we release it ASAP or wait for the next release and get
it to a couple of miners in the meantime (possibly with
auto-lowS-malleating)


- meeting conclusion

Contact miners about "Test LowS in standardness, removes nuisance
malleability vector" ( https://github.com/bitcoin/bitcoin/pull/6769 )
Release scheduled for the end of the month, together with likely
check-lock-time-verify and possibly check-sequence-verfiy.



**CLTV & CSV backport review**

- background

CLTV: checkLockTimeVerify
CSV: checkSequenceVerify
Both new time-related OP-codes.
Been discussed heavily last week.


- meeting comments

CSV doesn't seem ready enough for release later this month.
There's no clarity on how things look when all 3 time related pull-requests
are merged.
There's a number of people still reviewing the pull-requests.
Uncertainty and confusion about whether the semantics are final or not (in
regards to using bits from nSequence). nSequence are 4 bytes intended for
sequencing time-locked transactions, but this never got used.
Now these bytes are being repurposed for a mixture of things. Currently the
plan is: " bits 0..15 are the relative locktime, bit 30 determines units
(0: height, 1: time w/ 512s granularity), and bit 31 toggles BIP 68 (0: on,
1: off). bits 16..29 are masked off and can take any value."

- meeting conclusion

Clarification from maaku regarding nSequence for BIP68. (after the meeting
he explained he was waiting for opinions, but not enough people seemed to
know the issue at hand)
Continue review of pull requests 6312 (
https://github.com/bitcoin/bitcoin/pull/6312 ), 6564 (
https://github.com/bitcoin/bitcoin/pull/6564 ) and 6566 (
https://github.com/bitcoin/bitcoin/pull/6566 )


**Creation of bitcoin discuss mailing list**

- background

The bitcoin-dev mailing list is intented for technical discussions only.
There's things that don't belong there but need to be discussed anyway.
Now this is done in bitcoin-dev, but the volume of this is getting too big.

There's recently also an influx of really inappropriate posts, level
kindergarden (
https://www.mail-archive.com/bitcoin-dev@lists.linuxfoundation.org/msg02539.html
).


- meeting comments

No clarity about who are the moderators.
Next week there'll be a bitcoin-discuss list created.
Decisions are needed as to who'll become the moderators for that and
bitcoin-dev.
Decisions are needed as to what will be the list and moderation policies.


- meeting conclusion

The bitcoin-discuss list will be created as well as a simple website
listing all the lists and corresponding policies.
A meeting is scheduled on monday to discuss the moderation and policies of
said lists.


**Participants**

morcos           Alex Morcos
gmaxwell         Gregory Maxwell
wumpus           Wladimir J. van der Laan
sipa             Pieter Wuille
BlueMatt         Matt Corallo
btcdrak          btcdrak
petertodd        Peter Todd
warren           Warren Togami
phantomcircuit   Patrick Strateman
dstadulis        Daniel Stadulis
GreenIsMyPepper  ?? Jospeh Poon ??
bsm117532        Bob McElrath

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