wasm-secp256k1

The libsecp256k1 C library compiled to WASM and wrapped with an ultralight TypeScript API.

Supports four basic operations:

• Computing the corresponding public key for a given private key
• Signing
• Verifying
• ECDH

This module offers substantially greater security than pure JavaScript implementations of Secp256k1 due to the fact that JS runtimes simply make it impossible for JS developers to effectively mitigate side-channel attacks. Anyone who says otherwise doesn't know what they're talking about.

In addition to zero-ing out private keys after use, the wrapper also randomizes the lib context every time a public key is computed or a message is signed.

Signature recovery is not currently enabled, but is easy to add. If you meed it, please open an issue.

Demo webapp and its source

Install

npm install @solar-republic/wasm-secp256k1

Usage

First, choose which import method suites your needs:

Default

Import with the WASM binary preloaded and uncompressed. No need to perform fetch, but bundle will be larger (+332 KiB).

import {initWasmSecp256k1} from '@solar-republic/wasm-secp256k1'
const secp256k1 = await initWasmSecp256k1();

Compressed

Import with the WASM binary preloaded and gzipped (requires access to globalThis.DecompressionSteam). No need to perform fetch, but bundle will be still be a bit larger (+175 KiB).

import {initWasmSecp256k1} from '@solar-republic/wasm-secp256k1/gzipped'
const secp256k1 = await initWasmSecp256k1();

Headless

Import without the WASM binary. Produces the smallest bundle size but requires fetching the binary yourself.

import {WasmSecp256k1} from '@solar-republic/wasm-secp256k1/headless';

// provide the binary (the constructor also accepts raw bytes)
const secp256k1 = await WasmSecp256k1(await fetch('secp256k1.wasm'));

Using the instance:

// generate a random private key
const sk = secp256k1.gen_sk()

// get its corresponding public key
const pk = secp256k1.sk_to_pk(sk);

// sign a message hash (caller is responsible for actually hashing the message and providing entropy)
const signed = secp256k1.sign(sk, messageHash, entropy);

// verify a given message hash is signed by some public key
const verified = secp256k1.verify(signed, messageHash, pk);

// derive a shared secret with some other's public key
const shared = secp256k1.ecdh(sk, otherPk);


// zero out private key
sk.fill(0, 0, 32);

Caller is responsible for zero-ing out private keys in the Typed Arrays it passes. Library only zeroes out the bytes in the copies it makes.

API

/**
 * Creates a new instance of the secp256k1 WASM and returns its ES wrapper
 * @param z_src - a Response containing the WASM binary, a Promise that resolves to one,
 * 	or the raw bytes to the WASM binary as a {@link BufferSource}
 * @returns the wrapper API
 */
export declare const WasmSecp256k1 = (dp_res: Promisable<Response> | BufferSource): Promise<Secp256k1>;

/**
 * Wrapper instance providing operations backed by libsecp256k1 WASM module
 */
interface Secp256k1 {
    /**
    * Generates a new private key using crypto secure random bytes and without modulo bias
    * @returns a new private key (32 bytes)
    */
    gen_sk(): Uint8Array;

    /**
    * Asserts that the given private key is valid, throws otherwise
    * @param atu8_sk - the private key (32 bytes)
    * @returns the same `Uint8Array`
    */
    valid_sk(atu8_sk: Uint8Array): Uint8Array;

    /**
    * Computes the public key for a given private key
    * @param atu8_sk - the private key (32 bytes)
    * @param b_uncompressed - optional flag to return the uncompressed (65 byte) public key
    * @returns the public key (compressed to 33 bytes by default, or 65 if uncompressed)
    */
    sk_to_pk(atu8_sk: Uint8Array, b_uncompressed?: boolean): Uint8Array;

    /**
    * Signs the given message hash using the given private key.
    * @param atu8_sk - the private key
    * @param atu8_hash - the message hash (32 bytes)
    * @param atu8_entropy - optional entropy to use
    * @returns compact signature (64 bytes) as concatenation of `r || s`
    */
    sign(atu8_sk: Uint8Array, atu8_hash: Uint8Array, atu8_ent?: Uint8Array): Uint8Array;

    /**
    * Verifies the signature is valid for the given message hash and public key
    * @param atu8_signature - compact signature in `r || s` form (64 bytes)
    * @param atu8_msg - the message hash (32 bytes)
    * @param atu8_pk - the public key
    */
    verify(atu8_signature: Uint8Array, atu8_hash: Uint8Array, atu8_pk: Uint8Array): boolean;

    /**
    * ECDH key exchange. Computes a shared secret given a private key some public key
    * @param atu8_sk - the private key (32 bytes)
    * @param atu8_pk - the public key (33 or 65 bytes)
    * @returns the shared secret (32 bytes)
    */
    ecdh(atu8_sk: Uint8Array, atu8_pk: Uint8Array): Uint8Array;

	/**
	 * Tweak the given private key by adding to it
	 * @param atu8_sk - the private key (32 bytes)
	 * @param atu8_tweak - the tweak vector (32 bytes)
	 * @returns the tweaked private key
	 */
	tweak_sk_add(atu8_sk: Uint8Array, atu8_tweak: Uint8Array): Uint8Array;

	/**
	 * Tweak the given private key by multiplying it
	 * @param atu8_sk - the private key (32 bytes)
	 * @param atu8_tweak - the tweak vector (32 bytes)
	 * @returns the tweaked private key
	 */
	tweak_sk_mul(atu8_sk: Uint8Array, atu8_tweak: Uint8Array): Uint8Array;

	/**
	 * Tweak the given public key by adding to it
	 * @param atu8_pk - the public key (33 or 65 bytes)
	 * @param atu8_tweak - the tweak vector (32 bytes)
	 * @returns the tweaked public key
	 */
	tweak_pk_add(atu8_pk: Uint8Array, atu8_tweak: Uint8Array, b_uncompressed?: boolean): Uint8Array;

	/**
	 * Tweak the given public key by multiplying it
	 * @param atu8_pk - the public key (33 or 65 bytes)
	 * @param atu8_tweak - the tweak vector (32 bytes)
	 * @returns the tweaked public key
	 */
	tweak_pk_mul(atu8_pk: Uint8Array, atu8_tweak: Uint8Array, b_uncompressed?: boolean): Uint8Array;
}

Is libsecp256k1 modified?

No, the library is imported as a git submodule directly from upstream.

Building from source

Prerequisites:

• Docker
• Bun - a drop-in replacement for Node.js with native support for executing TypeScript

git clone --recurse-submodules https://github.com/SolarRepublic/wasm-secp256k1
cd wasm-secp256k1
bun install
bun run build

The WASM binary will be output to public/out/secp256k1.wasm.

The Emscripten-generated js file at public/out/secp256k1.js is not needed for production if you are using the provided wrapper.

See also

hash-wasm is a great library that provides performant hashing using optimized WASM binaries. Though its API is asynchronous, it also provides an undocumented synchronous API.