read.py

import base64
import nfc.snep
import serial

from nacl.public import PublicKey, PrivateKey, Box

print('Waiting for NFC tag')

clf = nfc.ContactlessFrontend('usb')
tag = clf.connect(rdwr={'on-connect': lambda t: False})

print('Reading')

uid = None
prv = None

for record in tag.ndef.records:
    if record.name == 'touchkey:uid':
        uid = record.text
    elif record.name == 'touchkey:prv':
        prv = PrivateKey(base64.b64decode(record.text))

if uid is None or prv is None:
    print('Error: Invalid tag')
    exit()

print('Key ID: %s' % uid)
print('Loading key')

with open('./keys/%s.pub' % uid, 'rb') as reader:
    pub = PublicKey(reader.read())

with open('./keys/%s.key' % uid, 'rb') as reader:
    key = reader.read()

box = Box(prv, pub)

print('Decrypting')

plain = box.decrypt(key)

print('Sending to Arduino')

connection = serial.Serial('/dev/ttyS0', 9600)
connection.write(('%s\n' % (plain.decode())).encode())
connection.close()

print('All done!')