def aead_chacha20poly1305_encrypt(key: bytes, nonce: bytes, aad: bytes,
msg: bytes) -> Tuple[bytes, bytes]:
keyblock0 = chacha20_block(key, 0, nonce)
mac_key = keyblock0[0:32]
ciphertext = chacha20_encrypt(key, 1, nonce, msg)
len, to_mac = padded_aad_msg(aad, ciphertext)
mac = poly1305_mac(to_mac, mac_key)
return ciphertext, mac
def aead_chacha20poly1305_encrypt(key: key_t, nonce: nonce_t, aad: vlbytes_t,
msg: vlbytes_t) -> Tuple[vlbytes_t, tag_t]:
keyblock0 = chacha20_block(key, uint32(0), nonce)
mac_key = keyblock0[0:32]
ciphertext = chacha20_encrypt(key, uint32(1), nonce, msg)
len, to_mac = padded_aad_msg(aad, ciphertext)
mac = poly1305_mac(to_mac, mac_key)
return ciphertext, mac
def chacha20_aead_decrypt(aad: bytes, key: bytes, nonce: bytes,
ciphertext: bytes):
otk = poly1305_key_gen(key, nonce)
plaintext = chacha20_encrypt(key, 1, nonce, ciphertext)
mac_data = aad + pad16(aad)
mac_data += ciphertext + pad16(ciphertext)
mac_data += num_to_8_le_bytes(len(aad))
mac_data += num_to_8_le_bytes(len(ciphertext))
tag = poly1305_mac(mac_data, otk)
return (plaintext, tag)