ECDSA PrivateKey sometime generates less than 32 bytes raw key

[ar-conmit]

Description

There are cases when the generated ECDSA private keys are with different lengths.

The full private key(with DER header) is generated fine. The raw private key sometime is 31-bytes long.

Example:

• full key 3030020100300706052b8104000a04220420a5c09853a1628353f4bd0eb6acf5d89c3a90fc2a9dc2caf44c9aabdf96640b00
• raw key a5c09853a1628353f4bd0eb6acf5d89c3a90fc2a9dc2caf44c9aabdf96640b

It seems the raw key is not extracted successfully, the last 00 are missing. This behaviour is observed once in a while.

If the full key is provided to the SDK, the raw key is extracted successfully: PrivateKey.fromStringECDSA('3030020100300706052b8104000a04220420a5c09853a1628353f4bd0eb6acf5d89c3a90fc2a9dc2caf44c9aabdf96640b00').toStringRaw()

-> a5c09853a1628353f4bd0eb6acf5d89c3a90fc2a9dc2caf44c9aabdf96640b00

The issue occurs only in the generation process

Steps to reproduce

Once in n times the generated raw key will be 31 bytes long

(() => {
    let tries = 0;
    setInterval(() => {
        tries++;

        const pk = PrivateKey.generateECDSA();
        const raw = pk.toStringRaw();
        const der = pk.toStringDer();

        if (raw.length < 64) {
            console.log({ try: tries, raw, der, rawLength: raw.length, derLength: der.length });
            process.exit(0);
        }
    }, 300);
})();

after some time, the following response will be printed out

{
  try: 29,
  raw: 'c1069f71c4b9755df5ca95bda49c8fcec0eb1e51576f3d0d6bedcd469e9af8',
  der: '3030020100300706052b8104000a04220420c1069f71c4b9755df5ca95bda49c8fcec0eb1e51576f3d0d6bedcd469e9af800',
  rawLength: 62, <--- 31 bytes
  derLength: 100
}

Additional context

The following change seems to fix the issue

in cryptography/ECDSAPrivateKey.js file

toBytesRaw() {
    return this._keyPair.privateKey.slice(0, 32);
}

to be

toBytesRaw() {
    const bytes = new Uint8Array(32);
    bytes.set(this._keyPair.privateKey.slice(0, 32), 0)
    return bytes;
}

Hedera network

other

Version

2.17.0

Operating system

macOS

[janaakhterov]

@ar-conmit Thanks for such a well documented issue. I didn't even consider that we may be only returning 31 bytes instead of 32. Since you've already put in the work to figure out what the fix should be perhaps making a PR and getting credit for it would make sense? If no that's completely fine too.