On Wed, Oct 21, 2015 at 10:26 AM Gregory Maxwell <gmaxwell@gmail.com> wrote:

On Wed, Oct 21, 2015 at 7:48 AM, Gregory Maxwell <gmaxwell@gmail.com> wrote:
> I'm still sad that uniform segregated witeness is so hard to deploy,
> adding another id to every utxo set won't be a nice cost. :( But I
> have been trying for a long time to come up with anything better and
> not being successful.

Oh good. Luke solved it.

To deploy SW without a disruptive flag day this encoding could be used:

A new P2SH like scriptPubkey type is defined. In the soft-fork, the
scriptsig for this scriptPubkey is required to be empty.

Signatures are not covered under txid, but carried along side. Then
committed to in blocks in a separate hashtree.

Isn't that sort of what this BIP describes as well? Except that we use the scriptSig to transport the signatures internally to the transactions and strip them when it comes to signing/checking? The wire format and transport of transactions do not change so old clients continue to fetch and process transactions as before, they just can't verify the TX. Blocks still reference the instance but verification uses the stripped TX with the signatures on the side, etc.

 

The only disadvantage to the approach used in elements alpha that I
can come up with so far (in the few minutes since luke turned my can't
into a can) is that that the approach in EA did not disrupt the normal
relay handling process, and this would, since relay that transports
the extradata either needs to use a different hash that includes the
witness, or have a separate mechanism for witness transport.