hashkit

hashkit computes Meta's PDQ (image) and TMK+PDQF (video) perceptual hashes from raw pixel data, backed by a frozen, NCMEC-cross-checked conformance vector suite. It is for trust-and-safety and platform teams who need to match user-generated content against known-CSAM hash lists and prove their hashes are byte-identical to the reference.

Install

cargo add digitalharm-hashkit

The crate is published as digitalharm-hashkit but imported as hashkit (e.g. use hashkit::...).

What it does

• Computes a 256-bit PDQ image hash plus a 0–100 quality score from a single-channel luma buffer.
• Offers a PDQ-Dihedral variant that returns 8 hashes for the dihedral transforms (4 rotations × 2 mirrors) for robustness to rotation and mirroring.
• Compares hashes by Hamming distance (0–256 bits); matches are typically below a threshold of 31.
• Takes raw RGB/luma planes, never image codecs — the host decodes, keeping the core deterministic across runtimes.
• Ships zero hash lists: the algorithm lives here, the known-CSAM lists stay with NCMEC, IWF, and Project Arachnid.
• Is gated on a versioned conformance corpus so a release fails closed on any one-bit drift from the reference.

Quickstart

use hashkit::pdq;

// `luma` is single-channel, row-major, 1 byte per pixel.
// Decode and downsample to luma yourself (hashkit takes no image codecs).
let result = pdq::hash_from_luma(&luma, width, height)?;

println!("hash:    {}", result.hash.to_hex());
println!("quality: {}", result.quality.0);

// Two hashes are a likely match when their Hamming distance is below ~31.
let distance = result.hash.hamming(&other.hash);
let is_match = distance < 31;

Status

Pre-release: the first crates.io publish is still pending. PDQ image hashing (hash_from_luma and hash_dihedral_from_luma) is implemented by delegating to the maintained pdqhash crate, while the conformance corpus, WebAssembly bindings, and TMK+PDQF video features are still in progress toward v1.0. Pin versions and expect APIs to move before the first stable release.

Source

packages/hashkit