Verify without Etch

# Etch's own verdicts — then check them yourself with the canonical string.
curl https://test.etch.so/api/v1/verify/$ETCH_ID

# Re-hash the published string with any SHA-256 tool:
curl -s https://test.etch.so/api/v1/verify/$ETCH_ID | jq -j .canonical_string | shasum -a 256

// Fold an etch to its root. Tag bytes are prepended as BYTES, not as text.
// From tree version 2 a leaf also names its author: user id, then hash.
// treeVersion is etch.chain.tree_version; userId is etch.author.user_id.
const sha = async (...parts) => {
  const len = parts.reduce((n, p) => n + p.length, 0)
  const buf = new Uint8Array(len)
  let at = 0
  for (const p of parts) { buf.set(p, at); at += p.length }
  return hex(await crypto.subtle.digest('SHA-256', buf))
}
const toBytes = (h) => Uint8Array.from(h.match(/../g).map(b => parseInt(b, 16)))

const record = treeVersion === 1 ? hash : userId.replaceAll('-', '') + hash
let acc = await sha(Uint8Array.of(0x00), toBytes(record))     // leaf
for (const sibling of proof) {
  const [lo, hi] = acc <= sibling ? [acc, sibling] : [sibling, acc]
  acc = await sha(Uint8Array.of(0x01), toBytes(lo), toBytes(hi))  // node
}
console.log(acc === root)

// Read a batch manifest from Arweave and rebuild the tree yourself.
// This is the whole decoder. A manifest is sorted, fixed-width records:
//   tree version 1: the etch hash                        32 bytes
//   tree version 2: the author's user id, then the hash  48 bytes
// treeVersion is in the batch's attestation, beside the manifest's id.

const res = await fetch(`https://arweave.net/${manifestTx}`)
const bytes = new Uint8Array(await res.arrayBuffer())
const width = treeVersion === 1 ? 32 : 48

const records = []
for (let i = 0; i < bytes.length; i += width) {
  records.push([...bytes.subarray(i, i + width)]
    .map(b => b.toString(16).padStart(2, '0')).join(''))
}

// records is already sorted — that is how the tree was built, so this
// rebuilds the exact root and regenerates any etch's proof. From version 2
// it also says whose etch each leaf is: the first 32 characters are the
// author's user id without its dashes.