* Adds a type that has the name `EncryptedType`. This type gives
the possibility to encrypt a value, so that in the database exists
the encrypted form of the value and not the original one. When
a value needs to be read(and is of type `EncryptedType`) the value
automatically decrypted in order to present to the user.
* Two encryption/decryption engines are currently implemented.
One is using the AES algorithm and the other is using the
Fernet algorithm. These are implemented in a library that is
called Cryptography.
* Inside the tests folder there is a test whose name is
`test_encrypted` and tests the functionality of the above type.
* Inside the `encrypted.py` file there is documentation with a
complete example. Also the `data_types.rst` is modified in order
to add a section for the `EncryptedType`.
Signed-off-by: Konstantinos Kostis <konstantinos.kostis@cern.ch>
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