ansible-vault unexpected exception on Ubuntu

When attempting to edit an ansible-vault file…

ansible-vault edit roles/cassandra_backup/vars/test_s3_cfg.yaml 

The following error was received…

ERROR! Unexpected Exception, this is probably a bug: from_buffer() cannot return the address of the raw string within a str or unicode or bytearray object

Encountered on this version of Ubuntu…

Linux xxxxxxxxx 4.15.0-43-generic #46~16.04.1-Ubuntu SMP Fri Dec 7 13:31:08 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

The full python stacktrace can be viewed as follows…

ansible-vault edit roles/cassandra_backup/vars/test_s3_cfg.yaml -vvv
Traceback (most recent call last):

  File "/usr/local/bin/ansible-vault", line 118, in 

    exit_code = cli.run()

  File "/usr/local/lib/python2.7/dist-packages/ansible/cli/vault.py", line 255, in run

    self.execute()

  File "/usr/local/lib/python2.7/dist-packages/ansible/cli/__init__.py", line 155, in execute

    fn()

  File "/usr/local/lib/python2.7/dist-packages/ansible/cli/vault.py", line 446, in execute_edit

    self.editor.edit_file(f)

  File "/usr/local/lib/python2.7/dist-packages/ansible/parsing/vault/__init__.py", line 953, in edit_file

    plaintext, vault_id_used, vault_secret_used = self.vault.decrypt_and_get_vault_id(vaulttext)

  File "/usr/local/lib/python2.7/dist-packages/ansible/parsing/vault/__init__.py", line 736, in decrypt_and_get_vault_id

    b_plaintext = this_cipher.decrypt(b_vaulttext, vault_secret)

  File "/usr/local/lib/python2.7/dist-packages/ansible/parsing/vault/__init__.py", line 1316, in decrypt

    b_key1, b_key2, b_iv = cls._gen_key_initctr(b_password, b_salt)

  File "/usr/local/lib/python2.7/dist-packages/ansible/parsing/vault/__init__.py", line 1158, in _gen_key_initctr

    b_derivedkey = cls._create_key_cryptography(b_password, b_salt, key_length, iv_length)

  File "/usr/local/lib/python2.7/dist-packages/ansible/parsing/vault/__init__.py", line 1131, in _create_key_cryptography

    b_derivedkey = kdf.derive(b_password)

  File "/usr/local/lib/python2.7/dist-packages/cryptography/hazmat/primitives/kdf/pbkdf2.py", line 50, in derive

    key_material

  File "/usr/local/lib/python2.7/dist-packages/cryptography/hazmat/backends/openssl/backend.py", line 307, in derive_pbkdf2_hmac

    key_material_ptr = self._ffi.from_buffer(key_material)

TypeError: from_buffer() cannot return the address of the raw string within a str or unicode or bytearray object

This is due to a problem with packages instakll via apt and pip. It can be fixed with the following procedure…

sudo -E pip uninstall cryptography -y
sudo -E apt-get purge python3-cryptography
sudo -E apt-get autoremove
sudo -E pip3 install --upgrade cryptography

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