ec-nov-2.py

# exercise 2, generating shared key

from tinyec import registry
import secrets

curve = registry.get_curve('brainpoolP256r1')


def compress_point(point):
    return hex(point.x) + hex(point.y % 2)[2:]


def generate_shared_key(priv_key, pub_key):
    return pub_key * priv_key


def main():
    priv_key = secrets.randbelow(curve.field.n)
    pub_key = priv_key * curve.g

    alice_keys = priv_key, pub_key

    print('Alice\'s key pair')
    print('private', hex(alice_keys[0]))
    print('public')
    print('x', hex(alice_keys[1].x),
          '\n'
          'y', hex(alice_keys[1].y))

    priv_key = secrets.randbelow(curve.field.n)
    pub_key = priv_key * curve.g

    bob_keys = priv_key, pub_key

    print()
    print('Bob\'s key pair')
    print('private', hex(bob_keys[0]))
    print('public')
    print('x', hex(bob_keys[1].x),
          '\n'
          'y', hex(bob_keys[1].y))

    sh_key_1 = generate_shared_key(bob_keys[0], alice_keys[1])
    sh_key_2 = generate_shared_key(alice_keys[0], bob_keys[1])

    assert sh_key_1 == sh_key_2, 'Error in key pair generation, sh key generation has failed'


if __name__ == '__main__':
    main()