How to convert public key (64 bytes) to compressed public key (33 bytes)

Question

I currently have a generated 64-byte public key that has been recovered from an Ethereum transaction.

How do I convert this key into a 33-byte compressed public-key? The problem I'm having seems pretty trivial but I cannot for the life of me find a solution! I'm currently working with javascript.

Any help would be greatly appreciated.

Answer 1

There's a package that contains suitable functions, here -> pubkey/eth-crypto

See:

• publicKey.compress(), and
• publicKey.decompress()

The compress code is below. (Copy + pasted from this file.)

var _secp256k = require('secp256k1');

function compress(startsWith04) {

    // add trailing 04 if not done before
    var testBuffer = Buffer.from(startsWith04, 'hex');
    if (testBuffer.length === 64) startsWith04 = '04' + startsWith04;

    return (0, _util.uint8ArrayToHex)((0, _secp256k.publicKeyConvert)((0, _util.hexToUnit8Array)(startsWith04), true));
}