Extract Public Key

Pull the public half out of whatever you have: a certificate, a CSR, or a private key in PKCS#8, PKCS#1 or SEC1 form. The result is a PUBLIC KEY PEM, the same bytes openssl x509 -pubkey would give you, along with the key's algorithm and size. RSA and EC keys are supported; an Ed25519 private key does not carry its public half in the clear.