[Bitcoin-segwit2x] F2Pool backing out of NYA - Fork still happening?

David A. Harding dave at dtrt.org
Sun Oct 15 11:57:53 UTC 2017

On Sat, Oct 14, 2017 at 10:13:01AM -0700, Mike Belshe via Bitcoin-segwit2x wrote:
> a) The SPV wallets will follow the longest chain
> [...]
> c) You claim that "most smart phone wallets" will not follow the longest
> chain.  I believe this is untrue.  Can you tell me which wallets you're
> referring to?

I'm not Adam, and I don't even know if these two points were supposed to
be related, but I did want to note that several SPV wallets don't use
the peer-to-peer network even though they do check SPV inclusion proofs.

For example, an Electrum wallet connects to an Electrum server that
itself gets information from a particular Bitcoin Core-compatible full
node (Core, ABC, Unlimited, btc1, etc).  

    Wallet <-> Electrum Server <-> Node

Whatever node the server operates determines which chain the wallet user
sees transactions for.  Electrum does provide SPV proofs to wallets to
prove to the user that their transactions connect to the node's header
chain, and there is a secure initial header download that prevents
someone from tricking clients with a difficulty-1 chain, but ultimately
Electron users don't necessarily follow the strongest chain.

We saw this particularly at work during the 4 and 5 July 2015 accidental
forks where some pre-0.10 Electrum servers would return the invalid
chain and some 0.10+ servers would return the valid chain.

Of the 11 mobile wallets currently listed on
https://bitcoin.org/en/choose-your-wallet, five connect to the P2P network
directly and so are likely to follow the strongest valid chain of headers
they see[1]:

    user at devbco:~/bitcoin.org/_wallets$ git grep -l 'compat.*mobile' | xargs grep -l spvp2p

Seven do not use the P2P network and will not follow a chain their
server's nodes consider invalid.

    user at devbco:~/bitcoin.org/_wallets$ git grep -l 'compat.*mobile' | xargs grep -L spvp2p

This is obviously not a comprehensive survey of all mobile wallets.

Hopefully that helps,


[1] As discussed elsewhere in this thread, this may not necessarily be
the strongest chain in existence if the P2P SPV clients are unable to
connect to nodes serving that chain.
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