def decrypt_json(enc, keys):
"""
Takes the object returned by encrypt_json earlier, and returns
the original input object using the given keys.
"""
nonce, cipher, tag = map(b64_decode, [enc['nonce'], enc['cipher'], enc['tag']])
kconf, kauth = keys
ourtag = hmac.new(kauth, nonce + cipher, sha256).digest()
if len(nonce) != 8 or not hmac.compare_digest(ourtag, tag):
raise IOError('corrupt ciphertext')
plain = chacha.chacha20_cipher(kconf, nonce, cipher)
plain = crypto.unpad(plain)
return json.loads(plain.decode('utf8'))
def encrypt_json(js, keys, padding):
"""
Encrypt the json-encodable object js using the keys
provided (get these from a secrets object).
This returns a dict with items for the things you need
to decrypt.
"""
nonce = os.urandom(8)
plain = json.dumps(js).encode('utf8')
plain = padding(plain)
kconf, kauth = keys
cipher = chacha.chacha20_cipher(kconf, nonce, plain)
tag = hmac.new(kauth, nonce + cipher, sha256).digest()
return dict(
tag = b64_encode(tag),
cipher = b64_encode(cipher),
nonce = b64_encode(nonce)
)