hh turns a blockchain address, a public key or any hash into a small deterministic picture that a person can compare at a glance: a 4 x 4 matrix of solid squares, circles and triangles in four colours. It exists to catch address poisoning and clipboard substitution, which work because people check only the first and last characters of a long string. The colours are chosen so that people with a colour vision deficiency can tell them apart as well.
0x1234567890abcdef00112233445566778899aabb |
0x12345678f1e2d3c4b5a69788796a5b4c8899aabb |
|---|---|
 |
 |
The two addresses agree in their first and last eight hex digits. Their pictures are unrelated.
This is the TypeScript implementation, published on npm as @censync/hh. It has no dependencies
and uses no platform API, so the same code runs in browsers, Node.js, Deno and Bun, and it
produces, byte for byte, the output of the C++ reference implementation
hh-cpp, which owns the
specification and the golden
vectors. testdata/ is a byte-identical copy of those vectors; testdata/SOURCE names the
hh-cpp release they came from.
Every implementation produces the same pictures, tags and encoded files, byte for byte, and its tests check it against a copy of the golden vectors of hh-cpp.
| Language | Repository | Package | Install |
|---|---|---|---|
| C++17, C ABI | hh-cpp, the reference: specification and golden vectors | CMake hh::hh, pkg-config hh (releases) |
CMake FetchContent or find_package(hh) |
| Kotlin and Java: JVM, Android | hh-kotlin | Maven Central io.github.censync:hh |
implementation("io.github.censync:hh:1.0.0") |
| TypeScript and JavaScript: browsers, Node.js, Deno, Bun | hh-ts (this repository) | npm @censync/hh |
npm install @censync/hh |
| Go | go-hh | github.com/censync/go-hh |
go get github.com/censync/go-hh |
| Python | hh-python | PyPI humanized-hash |
pip install humanized-hash |
A Sui address has 64 hex digits, and nobody reads 64 digits. The second address below differs from the first in one digit, the third in two; the changed digits are marked. In the text they are easy to miss. The pictures and the tags are unrelated, because every cell depends on every bit of the input.
| Picture | Address | Tag |
|---|---|---|
 |
0xeab3150efcb34ff74930d8f3d491be109070a39e4d380de7737aff5c72a0b6b2 |
B6P-65H |
 |
0xeab3150efcb34ff74930d8f8d491be109070a39e4d380de7737aff5c72a0b6b2 |
Q60-QKR |
 |
0xeab3150efcb34ff74930d8f3d491be109010a39e4d380dc7737aff5c72a0b6b2 |
ZSJ-7BK |
What a forger pays, by calculation. One current GPU tries about 1.4 billion addresses per second; a try against hh also has to compute the stretched base digest, which leaves about 680 000 tries per second. The figures are the expected search times on one such GPU for a typical picture (SECURITY.md of hh-cpp has the reasoning).
| The forged address has to match | Tries | One GPU |
|---|---|---|
| the first 4 and the last 4 hex digits | 2^32 | 3 seconds |
| the first 6 and the last 6 hex digits | 2^48 | 2.3 days |
| the first 8 and the last 8 hex digits | 2^64 | 420 years |
| the universal picture, with two cells allowed to differ | 2^52, stretched | 210 years |
| the universal picture, in every cell | 2^68, stretched | 14 million years |
| the ends of the text and the picture | the product of the two | |
| the keyed picture | cannot be searched: without the key the picture cannot be computed |
A lookalike of the text is cheap, which is why address poisoning works. A lookalike of the picture is not, and the two costs multiply. A picture that looks the same is still strong evidence rather than proof; the tag or the full address is the check that is certain.
- Two modes. A universal picture is the same for everyone and is what two people compare. A keyed picture is computed with a 32-byte secret of the wallet: an attacker who does not hold the key cannot compute, and therefore cannot grind, a lookalike. Inside an application keyed pictures are the default.
- Deterministic to the byte. Integer arithmetic only. The same input gives the same pixels and the same PNG, BMP and JPEG bytes as hh-cpp, in every JavaScript engine.
- Frozen. The algorithm has no version and never changes; a picture that a user has learned stays the same for ever. Library releases follow SemVer and never alter the output.
- No dependencies and no platform API: no Node.js modules, no DOM, no
TextEncoder, no WebCrypto, no WebAssembly. SHA-256, HMAC, PBKDF2, UTF-8, deflate and the image encoders are part of the library, and the compiler configuration keeps everything else out. ESM only, with type declarations and without side effects; about 16 kB gzip-compressed once the comments are stripped. - Made for colour vision deficiency. About one man in twelve does not see colours the way the rest do. The four colours were chosen for them: the palette was searched so that every pair stays apart under simulated protanopia, deuteranopia and tritanopia, and every colour keeps a contrast of 3:1 on white and on dark surfaces. Shape carries most of the information, so a picture still works in greyscale (the measurements are in docs/design of hh-cpp).
- Pixels, not pictures. The library returns RGBA pixels and encoded files; putting them on a
canvas or into an
<img>is two lines in the host.
hh answers one question: is this the same address as the one I mean? Wherever a person has to answer it from a long string, a picture answers it faster and more reliably than the first and last characters do.
- Sending and confirming. The picture of the recipient stands next to the address field and on the confirmation screen. A swapped or mistyped address changes it completely.
- Address books and account lists. Every saved payee and every account of the user carries its picture, so a list is scanned instead of read; 32 to 48 px is enough for recognition.
- Two devices of one user. An offline signer and the online device show the same picture for the same address, so the two screens are compared at a glance instead of 64 characters.
- Support, screenshots and voice. The six-character tag (
TKS-PVH) travels through chat and over the phone; the picture travels in a screenshot. - Documents and messages from a server. The encoders return PNG, BMP or JPEG bytes, so a backend puts the picture into a receipt, an invoice or an email without a graphics library.
- Anything that is a hash, not only an address. An SSH or PGP key fingerprint, a TLS certificate pin, an API key, the checksum of a backup or of a firmware image.
Three rules keep it honest: the picture complements the text check and never replaces it; inside one application keyed pictures are the default and universal pictures are what is shared with others; a picture that backs a decision is at least 64 dp and stands beside the picture it is compared with. docs/INTEGRATION.md has the rest.
npm install @censync/hhimport { BaseDigest, Fingerprint } from "@censync/hh";
const digest = BaseDigest.ofHex("0x5aAeb6053F3E94C9b9A09f33669435E7Ef1BeAed"); // slow: cache it
const fingerprint = Fingerprint.universal(digest); // or Fingerprint.keyed(digest, key)
const image = fingerprint.render(128); // 128 x 128 RGBA pixels
const pixels = new ImageData(new Uint8ClampedArray(image.rgba.buffer), image.width, image.height);
canvas.getContext("2d")!.putImageData(pixels, 0, 0);
const png: Uint8Array = image.encodePng(); // the same bytes in every implementation
const tag: string = fingerprint.tag; // "TKSPVH", shown as TKS-PVHInvalid arguments throw HhError, which carries the error of the specification as a number
(code) and as a name (specName, for example "invalid_hex"); the functions that take outside
data have ...OrNull companions. The package needs an ES2020 engine: every current browser,
Node.js 20 or newer, Deno, Bun. The type declarations need TypeScript 5.7 or newer.
A decision (confirming a payment, verifying a pasted address) should be backed by a picture of at least 64 CSS pixels, better 96, next to the picture it is compared with. Smaller pictures are for recognition in lists. See docs/INTEGRATION.md for browser, Node.js, React and Web Worker recipes and for keyed mode in a web application, and SECURITY.md of hh-cpp for what a picture proves and what it does not.
The cells, the palette and the geometry are fixed; the host chooses the shape, the background and, for a keyed picture, the marker. Every picture below is the address of the quick start, rendered at 128 px.
| Shape | Opaque white | Light blue E8EEF7 |
Transparent | Keyed, transparent |
|---|---|---|---|---|
| Square |  |
 |
 |
 |
| Round |  |
 |
 |
 |
- Background. Any colour with any transparency. Outside rounded corners and outside the disc the picture is transparent anyway, so a transparent background takes whatever is behind it: the two transparent columns above are the same bytes on a light page and on a dark one.
- Contrast. An opaque background is refused below 2:1 against a palette colour, and the
contrast report gives the WCAG ratio so that a host can warn below 3:1. White scores 300, the
light blue above 257,
121212scores 300; mid greys and saturated surfaces are what to avoid. - The frame marks the mode. A universal picture has no frame by default, a keyed square gets rounded corners, and the round shape stays unmarked unless a style is asked for (ticks above). Pick one style and keep it everywhere in an application.
- The round shape inscribes the same grid in a circle, so its cells are about a third smaller; give it a third more pixels.
const options: RenderOptions = {
shape: "round",
backgroundRgb: 0xe8eef7,
backgroundAlpha: 0, // transparent; the colour then does not matter
frame: "ticks", // a marker: keyed pictures only
};
const report = measureContrast(options);
if (report.figuresX100 < 300) { /* warn */ }A Node.js program that writes the picture of an address to a PNG file and prints its tag.
mkdir hh-example && cd hh-example
npm init -y
npm install @censync/hhmain.mjs:
import { writeFileSync } from "node:fs";
import { BaseDigest, Fingerprint } from "@censync/hh";
const digest = BaseDigest.ofHex("0x5aAeb6053F3E94C9b9A09f33669435E7Ef1BeAed");
const fingerprint = Fingerprint.universal(digest);
writeFileSync("address.png", fingerprint.render(128).encodePng());
const tag = fingerprint.tag;
console.log(`${tag.slice(0, 3)}-${tag.slice(3)}`);node main.mjs prints TKS-PVH and writes address.png, byte for byte the file
testdata/golden/evm-1-universal-128.png that every implementation reproduces. Saved as
main.mts, the same code is TypeScript: the package carries its type declarations.
Node.js 20 or newer. The toolchain is the TypeScript compiler and the type declarations of
Node.js, pinned in package-lock.json; tests run on the test runner that ships with Node.js.
npm ci
npm test # compiles everything and runs every test
tools/crosscheck.sh <path to hh_cli of hh-cpp> # differential test against hh-cpp
npm run bench # timings of the digest, the renderer, the encoders
npm pack --dry-run # what would be published
npm run build:dev # the command line tool, among the rest
node build/cli/hh-cli.js 0x5aAeb6053F3E94C9b9A09f33669435E7Ef1BeAed --out address.png
node build/cli/hh-cli.js --help| Directory | Purpose |
|---|---|
src |
the published library, compiled to dist/ without access to any platform API |
test |
the tests, including the golden vectors of hh-cpp |
cli |
command line tool for pictures and for the differential test; never published |
bench |
the benchmark; never published |
testdata |
the golden vectors, copied from hh-cpp by tools/update-vectors.sh |
tools |
the differential test with its hand-made cases, the vector update, the clean-up of build products |
docs |
the integration guide and the pictures of this file |
The rules for patches are in CONTRIBUTING.md, the releases in CHANGELOG.md.
MIT, see LICENSE. Copyright (c) 2026 Dmitry Mandrika. CenSync