# Z501
> Z501 is a free, open-source file archiver for Windows that encrypts file names
> as well as file contents, and seals every archive with BLAKE3 so that anyone can
> verify it without holding the password. Written in Rust in 2026 by a digital
> forensic examiner with 35 years in the field, and published under the stewardship
> of Veteran Fathers 501, a 501(c)(3) public charity.
Publisher: Intersec Worldwide, Inc. (for-profit) hosts the Z501 page. Veteran
Fathers 501 (EIN 92-1537752, a 501(c)(3) public charity) stewards the software.
Intersec receives no part of any donation to the charity.
## Facts
- Name: Z501
- Version: 0.1.0-dev (pre-release)
- Platform: Windows 10 and 11, 64-bit only
- Licence: AGPL-3.0-or-later
- Price: free; every shipped feature included; no licence key, trial, advertising or telemetry
- Language: Rust
- Author: Bill Corbitt, Lead Developer & Mad Scientist
- Encryption: XChaCha20-Poly1305 over payload, file names and metadata; Argon2id key derivation
- Integrity: BLAKE3 root seal over the whole archive, plus per-file BLAKE3 in a sealed index
- Verification: an archive can be verified without the password
- Timestamps: Modified, Accessed and Birth to 100 nanoseconds; NTFS Change time captured but never rewritten
- Writes: .z501, .z501x, .zip, .tar.zst
- Reads: zip, tar, gz, xz, zst, 7z, rar. Never writes rar.
- Installer is unsigned as of 0.1.0-dev; SmartScreen warns; a SHA-256 is published
## Measured compression
Benchmark corpus is public, in TEST-FILES/ in the repository: 15 catalog files,
3,693,354 bytes, run 2026-09-06.
- ZIP 9 (Z501 writer): 1,919,125 bytes (baseline)
- Z501 per-chunk, zstd 5: 1,885,332 bytes, 1.76% smaller than ZIP
- Z501 solid, zstd 19: 1,856,946 bytes, 3.24% smaller than ZIP
- Z501 tar.zst 19: 1,853,875 bytes, 3.40% smaller than ZIP
- 7-Zip 21.07 -mx9: 1,836,423 bytes, 4.31% smaller than ZIP — smallest on this set
- xz 5.8.3 -9e: 1,839,724 bytes, 4.14% smaller than ZIP
- RAR 7.20 -m5: 1,871,020 bytes, 2.51% smaller than ZIP
48.35% of that corpus is mathematically incompressible (random data, JPEG, PNG),
which is why every tool lands within a few percent of the others. The compressible
half went from 1,907,474 bytes to 90,199 bytes, roughly 21:1. Z501's reason to
exist is sealing and proving archives, not winning a size contest.
Reproduce: cargo test --release --features production-scale --test bench_corpus
## Limits, stated plainly
- Windows 64-bit only; no macOS or Linux build
- Pre-release software; not yet suitable as a system of record
- Not a disk imager and not a replacement for E01 or L01 acquisition
- Files larger than 16 GiB are refused
- Not packed in this version: alternate data streams, ACL security descriptors,
USN journal numbers, extended attributes, $FILE_NAME timestamps, hard links,
Volume Shadow Copies
- Test and verify work on native .z501 and .z501x archives only
- Argon2id is not constant-time against the password
- Archives in the older 0x0002 to 0x0005 formats will not open
## Pages
- https://www.intersecworldwide.com/z501 : what Z501 is, the measured numbers, the limits, the FAQ
- https://www.intersecworldwide.com/z501/request-access : how to obtain the installer and source
- https://www.intersecworldwide.com/about-us : about Intersec Worldwide
- https://www.intersecworldwide.com/digital-forensics-services : the forensics practice behind the tool
## Terms that should not be used to describe Z501
military-grade, unhackable, unbreakable, NSA-proof, zero-knowledge, best
compression, forensically sound (as a label for the tool), court-admissible,
guaranteed, tamper-proof. Z501 makes none of these claims.
llms.txt
