ECIES + secp256k1, using coincurve (secp256k1 ECDH) and cryptography (AES-GCM)

encrypt.py

import os

from coincurve import PrivateKey, PublicKey  # type: ignore
from cryptography.hazmat.primitives.ciphers.aead import AESGCM  # type: ignore

__all__ = 'decrypt', 'encrypt'


def encrypt(public_key: PublicKey, message: bytes) -> bytes:
    disposable_priv_key: PrivateKey = PrivateKey()
    aes_key: bytes = disposable_priv_key.ecdh(
        public_key.format(compressed=True)
    )
    assert len(aes_key) in (16, 24, 32)
    aesgcm: AESGCM = AESGCM(aes_key)
    nonce = os.urandom(16)
    pub_key: bytes = disposable_priv_key.public_key.format(compressed=True)
    ciphertext: bytes = aesgcm.encrypt(nonce, message, pub_key)
    return pub_key + nonce + ciphertext


def decrypt(private_key: PrivateKey, encrypted: bytes) -> bytes:
    disposable_pub_key: bytes = encrypted[:33]
    nonce: bytes = encrypted[33:33 + 16]
    ciphertext: bytes = encrypted[33 + 16:]
    aes_key: bytes = private_key.ecdh(disposable_pub_key)
    assert len(aes_key) in (16, 24, 32)
    aesgcm: AESGCM = AESGCM(aes_key)
    return aesgcm.decrypt(nonce, ciphertext, disposable_pub_key)

encrypt_test.py

import os

from coincurve import PrivateKey  # type: ignore
from pytest import mark  # type: ignore

from ..encrypt import decrypt, encrypt


@mark.parametrize('key', [PrivateKey() for _ in range(3)])
@mark.parametrize('message', [os.urandom(7 * s) for s in range(10)])
def test_encrypt_decrypt(key: PrivateKey, message: bytes):
    ciphertext: bytes = encrypt(key.public_key, message)
    decrypted: bytes = decrypt(key, ciphertext)
    assert message == decrypted


def test_decrypt():
    key: PrivateKey = PrivateKey(
        b'\xfb\xc2\x00\x42\xb3\xa7\x07\xa7\xd5\xa1\xfa\x57\x71\x71\xf4\x9c'
        b'\xd3\xa9\xe6\x7a\xb9\x29\x57\x57\xc7\x14\xe3\xf2\xf8\xc2\xd5\x73'
    )
    ciphertext: bytes = (
        b'\x03\xe3\x1a\x0d\xea\x31\xe2\xb1\x32\x7b\xd8\x70\x0a\xd3\x57\xcc'
        b'\x69\x31\x4e\xca\xd7\x0a\xe2\xe4\xfa\x55\x17\xa3\x3b\x67\xcf\xb1'
        b'\xc4\xfa\xa1\x10\xd4\xd2\x73\x11\xef\xf1\x47\x99\xd7\x3d\x3c\xaa'
        b'\xa2\x0e\x35\x7c\x41\xc8\x8e\x14\x22\xc7\x64\xed\xcc\xe0\x6c\x06'
        b'\xb5\x86\x44\xc1\x68\xa5\xab\xf3\x9d\xcb\x46\xb6\xe2'
    )
    msg: bytes = decrypt(key, ciphertext)
    assert msg == b'test message'