Dear list,

I find it hard to understand why a full node that does initial block

download also must download witnesses if they are going to skip

verification anyway. If my full node skips signature verification for

blocks earlier than X, it seems the reasons for downloading the

witnesses for those blocks are:

* to be able to send witnesses to other nodes.

* to verify the witness root hash of the blocks

I suppose that it's important to verify the witness root hash because

a bad peer may send me invalid witnesses during initial block

download, and if I don't verify that the witness root hash actually

commits to them, I will get banned by peers requesting the blocks from

me because I send them garbage.

So both the reasons above (there may be more that I don't know about)

are actually the same reason: To be able to send witnesses to others

without getting banned.

What if a node could chose not to download witnesses and thus chose to

send only witnessless blocks to peers. Let's call these nodes

witnessless nodes. Note that witnessless nodes are only witnessless

for blocks up to X. Everything after X is fully verified.

Witnessless nodes would be able to sync faster because it needs to

download less data to calculate their UTXO set. They would therefore

more quickly be able to provide full service to SPV wallets and its

local wallets as well as serving blocks to other witnessless nodes

with same or higher assumevalid block. For witnessless nodes with

lower assumevalid they can serve at least some blocks. It could also

serve blocks to non-segwit nodes.

Do witnessless nodes risk dividing the network in two parts, one

witnessless and one with full nodes, with few connections between the

parts?

So basically, what are the reasons not to implement witnessless

nodes?

Thank you,

/Kalle