How to use public key from a PEM file ?

[christopheblin]

I have the following python program

import base64
import ecdsa
import hashlib

digest = hashlib.sha256(b"Hello world").digest()
with open("key.pem") as f:
   public_key = ecdsa.VerifyingKey.from_pem(f.read())
signature = base64.b64decode("bxw1nS8Q39mnQVkAhvJctXuLHz4n0wUjLbE+phj1XlUeWDxl7DCK5bG4d7YrL7zGtAnUq3YT9AdrrAXjpwhCzQ==")

public_key.verify_digest(signature, digest)

pem file is :

-----BEGIN PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEOC76WxZ/TMzJnRqv/cy9llDqSIMW
lplgREY3jMxDCksPGDDyepeg7fFdCu56N9Br9n5oWmj/iKULrglQehGiiA==
-----END PUBLIC KEY-----

I'd like to compare with your library, but I do not find how to create the Point/Signature from the PEM :

    const digest = crypto.createHash('sha256').update(Buffer.from('Hello world')).digest();

    const publicKey = secp.Point.fromPem(fs.readFileSync('key.pem')); //How to do here ?

    const signature = Buffer.from(
      'bxw1nS8Q39mnQVkAhvJctXuLHz4n0wUjLbE+phj1XlUeWDxl7DCK5bG4d7YrL7zGtAnUq3YT9AdrrAXjpwhCzQ==',
      'base64',
    );
    
    const isSigned = secp.verify(signature, digest, publicKey);
    assert(isSigned)

I also have x/y in JWK (so base64) in case it is easier than PEM :

  {
    "crv": "P-256",
    "kty": "EC",
    "x": "OC76WxZ/TMzJnRqv/cy9llDqSIMWlplgREY3jMxDCks=",
    "y": "Dxgw8nqXoO3xXQruejfQa/Z+aFpo/4ilC64JUHoRoog="
  }

[paulmillr]

Use a separate module to convert binary to PEM. PEM is out of scope for noble.