EdDSA Poseidon

A JavaScript EdDSA library for secure signing and verification using Poseidon and the Baby Jubjub elliptic curve.

[!NOTE]
This library has been audited as part of the Semaphore V4 PSE audit: https://semaphore.pse.dev/Semaphore_4.0.0_Audit.pdf.

• Super lightweight: ~33kB (minified)
• Compatible with browsers and NodeJS
• TS type support
• Comprehensive code documentation
• Full test coverage

👾 Would you like to try it now? Explore it now on Ceditor!

References

1. Barry WhiteHat, Marta Bellés, Jordi Baylina. ERC-2494: Baby Jubjub Elliptic Curve. 2020-01-29. https://eips.ethereum.org/EIPS/eip-2494.
2. Lorenzo Grassi, Dmitry Khovratovich, Christian Rechberger, Arnab Roy, and Markus Schofnegger. POSEIDON: A New Hash Function for Zero-Knowledge Proof Systems. 2019. https://eprint.iacr.org/2019/458.pdf.

🛠 Install

npm or yarn

Install the @zk-kit/eddsa-poseidon package and its peer dependencies with npm:

npm i @zk-kit/eddsa-poseidon
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or yarn:

yarn add @zk-kit/eddsa-poseidon
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CDN

You can also load it using a script tag using unpkg:

<script src="https://unpkg.com/@zk-kit/eddsa-poseidon"></script>
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or JSDelivr:

<script src="https://cdn.jsdelivr.net/npm/@zk-kit/eddsa-poseidon"></script>
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📜 Usage

The public key is generated using BLAKE by default and BLAKE2 if specified in the import as follows: import { ... } from "@zk-kit/eddsa-poseidon/blake-2b".

import {
    derivePublicKey,
    signMessage,
    verifySignature,
    deriveSecretScalar,
    packPublicKey,
    unpackPublicKey
} from "@zk-kit/eddsa-poseidon"

// Your private key (secret).
const privateKey = "secret"
// The message you want to sign.
const message = "message"

// Derive a public key from the private key.
const publicKey = derivePublicKey(privateKey)

/*
[
    17191193026255111087474416516591393721975640005415762645730433950079177536248n,
    13751717961795090314625781035919035073474308127816403910435238282697898234143n
]
*/
console.log(publicKey)

// Sign the message.
const signature = signMessage(privateKey, message)

/*
{    
    R8: [
        12949573675545142400102669657964360005184873166024880859462384824349649539693n,
        18253636630408169174294927826710424418689461166073329946402765380454102840608n
    ],
    S: 701803947557694254685424075312408605924670918868054593580245088593184746870n
}
*/
console.log(signature)

const response = verifySignature(message, signature, publicKey)

// true.
console.log(response)

// Use this value as the input for your Circom circuit.
const secretScalar = deriveSecretScalar(privateKey)

/* 
6544992227624943856419766050818315045047569225455760139072025985369615672473
14277921624107172450683599157880963081763136590946434672207840996093731170206
*/
console.log(secretScalar)

// Pack the public key into a compressed format.
const packedPublicKey = packPublicKey(publicKey)

// 52359937820999550851358128406546520360380553803646081112576207882956925379784n
console.log(packedPublicKey)

// Unpack the compressed public key back into its original form.
const unpackedPublicKey = unpackPublicKey(packedPublicKey)

/*
[
    17191193026255111087474416516591393721975640005415762645730433950079177536248n,
    13751717961795090314625781035919035073474308127816403910435238282697898234143n
]
*/
console.log(unpackedPublicKey)

if (unpackedPublicKey) {
    console.log(publicKey[0] === unpackedPublicKey[0]) // true
    console.log(publicKey[1] === unpackedPublicKey[1]) // true
}
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