epochs

Epoch packages for the BLAKE2b chains: one file per 2016-block retarget epoch, carrying what a node needs to verify that epoch without the UTXO set, and the UTXO set commitment at both ends.

An epoch package (<chain>/<end height>.json, JSON-LD @type Epoch) holds:

• the block hash, coin count and MuHash of the UTXO set at the epoch's start and end, computed the way Core's gettxoutsetinfo muhash does it, so any Core-derived node with coinstatsindex can check them;
• a bitmap over the outputs the epoch created, saying which are still unspent at its end (the hints);
• the data of every older coin the epoch spent (the side data), which is what lets the blocks be validated with scripts on and no set to look coins up in.

Consecutive packages chain: each one's start is the previous one's end. The first package of a chain starts at an assumeUTXO snapshot. The format is produced and consumed by blaketestnode and will track the draft SwiftSync BIPs (455–457) as their coin format settles.

Chains

chain	network	packages	index
txbt4	btc:testnet4-blake2b	txbt4/	txbt4/index.json

<chain>/index.json lists every package with its sha256, size, heights, hashes, MuHash at both ends and the torrent's infohash, web seeds and magnet. The page at https://bitcoin-blake.github.io/epochs/ renders it.

Fetching

Each package is served three ways and the bytes are the same whichever you use:

• HTTPS from this repo on GitHub Pages, with CORS;
• HTTPS from the R2 bucket pub-8cae8bad22cf4f44b22188af9b1c0064.r2.dev/epochs/<chain>-<end>.json, with CORS and ranges;
• BitTorrent and WebTorrent: <chain>/<end>.json.torrent beside the package, with the two HTTPS copies as web seeds, so a swarm of zero peers still completes.

Check what you got: sha256sum <end>.json against index.json.

The open epoch

The epoch in progress, from the last boundary to the tip, is rebuilt every four hours and served from R2 as epochs/<chain>-current.json, for txbt4 https://pub-8cae8bad22cf4f44b22188af9b1c0064.r2.dev/epochs/txbt4-current.json. It has the same shape as a sealed package plus sealed: false and boundary, the height it seals at; its hints are provisional until then. It is mutable and not in this repo: when the boundary is reached it becomes <chain>/<boundary>.json here, with a torrent, and the open file starts over.

Verifying

git clone https://github.com/bitcoin-blake/blaketestnode && cd blaketestnode && npm install
node bin/blaketestnode.mjs epoch verify /path/to/153216.json --data <empty dir> --blocks-url <blocks url>

The verifier replays the epoch's blocks from the package and the served blocks alone, scripts on, and reports the end MuHash. It must equal end.muhash in the package, and in turn a node's gettxoutsetinfo muhash at that height.

Adding a package

node tools/index.mjs <chain>      # rebuilds <chain>/index.json from the packages and torrents present

Torrents are made with seeder/make-torrent.mjs from play-grounds/utxo-swarm, piece length 256 KiB, web seeds this repo and R2.