The protocol transcript (and other assets) from the original Sprout MPC have been restored to our S3 bucket. Check out the https://github.com/zcash/mpc repository for more information. I currently can’t archive these on the Internet Archive or put a torrent up, but I hope this will happen soon.

Background

The “Sprout” MPC ceremony took place over two years ago and produced the parameters used by the original “Sprout” shielded addresses in Zcash. We have since replaced these parameters with much more secure parameters produced in a newer and much larger ceremony. You can read more about that here. Our new “Sapling” shielded addresses use parameters built in the same ceremony.

If you’re interested, you can use the protocol transcript from that ceremony to verify that the parameters initially deployed in Zcash were constructed correctly.

Contrary to what I’ve seen people say recently, you do not need to verify the transcript to ensure that your privacy holds. (This would be unacceptable, considering verification of the transcript is expensive.) Our particular construction depends only on a property in the proving system (witness indistinguishability) that can be trivially guaranteed to hold without access to the transcript. I hope to write a blog post about things like this soon.

Timeline

The transcript was hosted publicly on an S3 bucket for about 18 months after the original launch of Zcash, but it was deleted or cleared out earlier this year. Probably due to its size, it was never archived on the Internet Archive. I began looking for a backup copy after some drama on Twitter appeared last month.

I once had a backup of the transcript, but the backup was on a laptop that had since been wiped. Others at the company were under the impression I had a backup, so I take responsibility for the delay. We were unable to find anyone that kept a copy of the transcript, because most that had downloaded it later deleted it due to its size. This meant that we had to reconstruct the transcript from the DVDs of the participants.

Because all of the participants archived their discs, we achieved this. Special thanks to Nat Kramer for recovering archives of the DVDs from Derek Hinch’s station, and Saleem Rashid for helping us recover Peter Todd’s DVD images. Thank you also to Andrew Miller and John Dobbertin for uploading their DVDs. And thank you to everyone else who looked for a copy on their computers!