secp256k1_nostr extension for PHP

secp256k1_nostr is a PHP 7.4+ extension to validate Nostr events in accordance to NIP-01.

It is implemented as a thick, opinionated wrapper around Bitcoin Core's libsecp256k1.

Sample Usage

<?php

$text = '
{
  "id": "62fa167369a603b1181a49ecf2e20e7189833417c3fb49666c5644901da27bcc",
  "pubkey": "84fdf029f065438702b011c2002b489fd00aaea69b18efeae8261c44826a8886",
  "created_at": 1689033061,
  "kind": 1,
  "tags": [],
  "content": "This event was created at https://nostrtool.com/ with a throwaway key.",
  "sig": "a67e8d286605e3d7dfd3e0bd1642f85a25bb0cd70ec2ed941349ac879f617868a3ffa2a9040bb43c024594a79e4878429a990298c51ae4d6d20533589f4a04df"
}';

$event = json_decode($text);

var_dump(secp256k1_nostr_verify($event->pubkey, $event->id, $event->sig));

// Mangle last half-byte of the signature on purpose
$event->sig[127] = 'e';

var_dump(secp256k1_nostr_verify($event->pubkey, $event->id, $event->sig));

The above script will output:

bool(true)
bool(false)

Installation (Linux)

These instructions are tailored for Ubuntu 22.04 LTS. Nevertheless, only the first step might be a bit different on other Linux distributions that don't use the APT package manager.

1. Install the required dependencies to build both the extension and secp256k1.

   $ sudo apt install autoconf build-essential git libtool php8.1-dev pkgconf

2. Clone this repository and its submodules.

   $ git clone https://github.com/1ma/secp256k1-nostr-php
   $ cd secp256k1-nostr-php
   $ git submodule init
   $ git submodule update

3. Build secp256k1 and the extension in one step. Then install the extension (secp256k1_nostr.so) in your local PHP. The 'install' command will likely require sudo privileges. Optionally, you can run the tests with make check before installing.

   $ make secp256k1 ext
   $ make check
   $ sudo make install

4. Append extension=secp256k1_nostr.so to your php.ini file. Note that often the PHP CLI and PHP-FPM have separate php.ini files, so you need to edit both. Finally, test that the extension loads correctly with php -m.

   $ echo "extension=secp256k1_nostr.so" | sudo tee -a /etc/php/8.1/cli/php.ini
   $ php -m | grep nostr
   secp256k1_nostr
   
   $ echo "extension=secp256k1_nostr.so" | sudo tee -a /etc/php/8.1/fpm/php.ini
   $ php-fpm8.1 -m | grep nostr
   secp256k1_nostr

Full API

See secp256k1_nostr.stub.php

F.A.Q.

How do I generate a private key?

A private key is just a random string of 32 bytes. The only caveat is that it has to be hex-encoded.

All functions of secp256k1_nostr only accept hex-encoded strings to lessen the friction of working with Nostr events.

   $privateKey = bin2hex(random_bytes(32));
   $publicKey = secp256k1_nostr_derive_pubkey($privateKey);

There is an exceedingly remote possibility that the bytes are out of range for a valid private key. In this case secp256k1_nostr_derive_pubkey() would throw an exception, but in practice this should never happen unless you deliberately feed the function a faulty private key such as 0000000000000000000000000000000000000000000000000000000000000000.

Are there stubs for the secp256k1_nostr functions?

Yes. Simply use Composer to install uma/secp256k1-nostr as a development dependency of your project:

$ composer require --dev uma/secp256k-nostr

NOTICE: This isn't a substitute for the real installation steps described above. This will just make the secp256k1_nostr.stub.php file visible to your IDE so that it's aware of the extension functions. But this does not install the extension, which is really the secp256k1_nostr.so file mentioned earlier.

What was the motivation for developing this extension?

I recently started working on a toy Nostr relay written in async PHP, and a central class in that project is the "Event" domain object that verifies its own signature at construction time.

As I wrote the first handful of unit tests I quickly found out that the existing PHP Schnorr libraries are very slow, therefore I built myself this native extension.

It can be used in any context where Nostr events need to be validated in PHP, not just relays.

How does this extension compare to secp256k1-php?

secp256k1-php is a generic binding to the libsecp256k1 library that exposes its full API function by function (also known as a "thin wrapper"). In contrast secp256k1_nostr is a "thick wrapper" that is tailored for Nostr event validation, in this case libsecp256k1 is just an implementation detail.

secp256k1_nostr could've been written on top of secp256k1-php as a regular PHP library, but unfortunately the project seems abandoned. As I write this it hasn't seen activity on the master branch for 4 years, and the code doesn't even compile on PHP 8.0 and up.

If you need a libsecp256k1 binding that exposes all its functionality you should try to revive that project.

Does secp256k1_nostr follow semantic versioning?

Yes, but the API may still evolve before the 1.0 release.

4. Major version zero (0.y.z) is for initial development.
   Anything MAY change at any time.
   The public API SHOULD NOT be considered stable.

Is Windows supported?

No, and I don't intend to work on this. But a PR would be welcome.

Is secp256k1_nostr available on PECL?

No :')