# Reconstruct your EPB3 page

Your private `address.epb` location file contains everything needed to reconstruct
its book. No account, submitted passage, database or EPB API is needed. Keep it
private: anyone holding it can reconstruct the book.

Save these linked files together from `/algorithm/epb3/`:

- [reconstruct.mjs](reconstruct.mjs)
- [epb3.js](epb3.js), [bytes.js](bytes.js), [constants.js](constants.js)
- [package.json](package.json), [package-lock.json](package-lock.json)
- [golden-vectors.json](golden-vectors.json)
- [specification.md](specification.md)

With Node.js 24 or later, run in that directory:

```sh
npm ci --ignore-scripts
node reconstruct.mjs --self-test
node reconstruct.mjs --address-file address.epb --page 173 --output page.txt
```

Installation needs the npm registry. Reconstruction afterward makes no network
calls. The page number is 1 through 410; internal indices are 0 through 409.
Output is a new private file, with 40 lines of 80 characters and a final newline.
Existing files are refused. This preserves mathematical characters; it does not
render the styled PDF or restore the original submitted punctuation/capitalization.
The short book ID and shelf labels cannot replace the complete location file.

Fixed synthetic examples cover one character, a short passage, a full page,
a multi-page passage and a complete volume. Self-test compares saved location,
first/final page and canonical digest hashes. These demonstrate repeatability;
they do not verify a purchase, a claim, package signatures or service availability.
The decoding files are a published extract of the versioned production engine.

EPB3 golden examples use **BLAKE3**, not SHA-256. `addressHash` hashes the exact
UTF-8 address; `firstPageHash` and `lastPageHash` hash the 3,200 raw base-29 digit
bytes of those pages, not the formatted text file. `digest` is the domain-separated
full-volume BLAKE3 identity defined in the specification. Private package file
hashes use SHA-256; the earlier EPB2 full-volume fixture also labels its SHA-256
values separately. These hash conventions must not be interchanged.

Reference implementation: Fly Strategic Group, LLC. No additional software license
grant is made here. `@noble/hashes` 2.4.0 by Paul Miller and contributors is installed
separately under its MIT license: https://github.com/paulmillr/noble-hashes.