#!/usr/bin/env python3

from base58 import b58decode
from base64 import b64decode, b64encode
from libnacl import crypto_sign_ed25519_sk_to_curve25519 as private_sign2crypt
from libnacl import crypto_sign_ed25519_pk_to_curve25519 as public_sign2crypt
from libnacl.sign import Signer, Verifier
from libnacl.public import SecretKey, PublicKey, Box

# solve this for poka
sender_pub = 'DCovzCEnQm9GUWe6mr8u42JR1JAuoj3HbQUGdCkfTzSr'
recip_seed = 'GA47R2WcyAw2GmEU8e2rYwYiLwLCZctfJtwzk87nhJpZ'
nonce = '482xiAewUx0RM6oLglHQG//0ySelpnL9'
title = 'LTmTBOGiakjGPGR7fCjWPnAVVFqkVjrmrxqY/iDWvdhWP+8oLtNgULScN2Rl/NifZGCA3LI='
content = 'YLVTaec04RoN9AMYNqVchnGknFipFTn3u06S/iCV84wuGLpsKoAsBbCfKci+7TsEdD7V3PQCyRSDANICRHuOiZOol1Svu87uQ3u1qwKSoAlcyloq1OdgTBNgkKCMkbQ0UYCsROr4bOuL8l3P7/xpK4+XFLwpmWCHuX+9fug6WovURlHSnVn8uYwuwn/ySF5CuYmULSXeU+1awrxDERdKPfysGYt2gi6DfX+LWd7ojbHPZTxvYlyjfgzG8bT6iDfFmtxUXEz9+3LpClewfZ7jdktaSM5dFE4+7CanBVQ='

signer = Signer(b58decode(recip_seed))
sk = SecretKey(private_sign2crypt(signer.sk))

verifier = Verifier(b58decode(sender_pub).hex())
pk = PublicKey(public_sign2crypt(verifier.vk))

box = Box(sk.sk, pk.pk)

plain_title = box.decrypt(b64decode(nonce) + b64decode(title))
plain_content =box.decrypt(b64decode(nonce) + b64decode(content))

# now lets build the ciphertext again for a full round trip
# poka's example used same keys for sender and recipient; we can reuse box
#
# libnacl.public.Box's encrypt() method prefixes the returned ciphertext 
# with a 24 byte nonce... whether sent in or not, 
# and the decrypt() method expects this nonce to be prefixed on the 
# ciphertext.
#
# show that poka's encrypted title is missing the 24b nonce
cipherbytes = box.encrypt(plain_title, nonce=b64decode(nonce))
assert cipherbytes[:24] == b64decode(nonce)
assert b64encode(cipherbytes[24:]).decode('utf-8') == title
# show that poka's encrypted content is missing the 24b nonce
cipherbytes = box.encrypt(plain_content, nonce=b64decode(nonce))
assert cipherbytes[:24] == b64decode(nonce)
assert b64encode(cipherbytes[24:]).decode('utf-8') == content
    
print(plain_title.decode('utf-8'))
print(plain_content.decode('utf-8'))

print('''
Thank you Poka, that was a frustrating and fun Sunday.  -Spencer971
8XVSTMVWoRmRoLkELEMqeSXjviRWTaTqttnr7evcgrrF
''')