Public key export deletes private key

[gR0OT]

When performing export_keys() in lightphe.init in case of exporting (publishing) the public key, it deletes private key in the process. This leaves the LightPHE object (who should have private key, because it generated it) unable to decrypt.

246: if public is True and keys.get("private_key") is not None:
247:     del keys["private_key"]

Current workaround:

gm = LightPHE('Paillier')
gm.export_keys('private.key', public=False)
gm.export_keys('public.key', public=True)
gm = LightPHE('Paillier', key_file='private.key')

Proposed fix:
Don't delete the private_key from keys when performing export_keys(), just export the public_key

pubkey = {'public_key': keys['public_key']}
with open(target_file, "w", encoding="UTF-8") as file:
    file.write(pubkey)

[serengil]

Closed with PR - #19