How to encrypt a message with the public-key of an Ethereum address

Question

I am writing some code in nodejs/browser. I have successfully created ethereum-addresses with the secp256k1-library. I was also able to sign and verify messages. Now I want to encrypt/decrypt a message with the public and private-key of the generated addresses. Has anyone done this before? Can I use CryptoJS to accomplish my goal?

Answer 1

thx @Edmunx Edgar, i tried to use ECIES, but it failed to install because of a subdepencency. I now used the bitcore-lib together with bitcore-ecies. This works like expected.

EDIT: I created a npm-module which does exactly theses things and also has some performance optimisations and tutorials: github:eth-crypto.

Here is my code for anyone with the same question:

// run 'npm install eth-crypto --save'

const EthCrypto = require('eth-crypto');

// create identitiy with key-pairs and address
const alice = EthCrypto.createIdentity();

const secretMessage = 'My name is Satoshi Buterin';
const encrypted = await EthCrypto.encryptWithPublicKey(
    alice.publicKey, // encrypt with alice's publicKey
    secretMessage
);

const decrypted = await EthCrypto.decryptWithPrivateKey(
    alice.privateKey,
    encrypted
);

if(decrypted === secretMessage) console.log('success');

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Answer 2

Assuming you have the public key of the person you want to send a message to (if they've already signed a transaction you can recover it from the signature) it should be possible to encrypt and decrypt using ECIES. Apparently there's a JavaScript library for this, I assume you can use it in a browser: https://bitcointalk.org/index.php?topic=627927.0

I have no idea either way whether or not these libraries are good enough to use securely.

Another approach is to generate a separate keypair that's actually designed for encryption, then use the Ethereum key to sign the public key and send it to the other party.