Core developer Greg Maxwell: Redeploying SegWit is "impossible" and requires waiting for the existing SegWit to expire

Core developer Greg Maxwell has given up hope on the upcoming Segregated Witness (SegWit) activation, saying that any SegWit redeployment “can’t possibly happen” before the current old SegWit expires.

Responding to the alleged agreement reached at Consensus 2017, led by Digital Currency Group CEO Barry Silbert, to activate SegWit in September, Maxwell explained why such a SegWit witness redeployment could not happen: due to technical reasons of “simplicity and security.”

Maxwell explained on Reddit:

The reason is that for simplicity and security reasons, all versions of Bitcoin that support SegWit only have the SegWit code path... for example, SegWit and non-SegWit transactions are not handled separately. SegWit is currently inactive with some very minor tweaks on top of it. This has the benefit of making SegWit easier to implement and minimizing changes to the network when SegWit is activated - it's not a bunch of dead code that can suddenly be turned on.

In versions after Core 0.13.1 (currently the latest version of Core is 0.14.1), almost all parts of SegWit have been activated, including all P2P components... new network service flags, witness transactions and block information, compact blocks v2, etc. To redeploy SegWit will require redefining all of these things.

If the old SegWit implementation had not expired, the Bitcoin network would have to support both SegWit versions. Then you would have code path duplication and a kind of joint testing problem.

To avoid these problems, BIP149 was not started.

But if the original SegWit expires, the change is a simple search and replace: no complicated joint testing, no path duplication, no dead code that will suddenly open up.

The main argument against BIP 148 previously was that it did not have to wait for the original SegWit to expire.

These challenges are not a hidden secret and have been discussed before with BIP148/149.

It sounds like this Silbert proposal was made entirely without the help of anyone who was involved in the discussion in detail.

Meanwhile, the Silbert protocol documentation has been published online, and participants said in a brief statement that they will "activate a 2MB hard fork on September 21, 2017."

“We are also working on the research and development of technical mechanisms to improve signaling in the Bitcoin community, as well as communication tools to enable ecosystem participants to more closely collaborate on the design, integration, and deployment of security solutions that increase the capacity of Bitcoin.”

Note: As previously reported, the current SegWit activation initial date is November 19, 2017.