How does TDE encrypt data?
==========================

TDE prevents unauthorized viewing of data in operating system files on
the database server and on backup storage. Data becomes unintelligible
for unauthorized users if it’s stolen or misplaced.

Data encryption and decryption is managed by the database and doesn’t
require application changes or updated client drivers.

EDB Postgres Advanced Server and EDB Postgres Extended Server provide
hooks to key management that’s external to the database. These hooks
allow for simple passphrase encrypt/decrypt or integration with
enterprise key management solutions. See :ref:`Securing the data encryption key <Securing the data encryption key>`  for more
information.

How does TDE affect performance?
--------------------------------

The performance impact of TDE is low. For details, see the `Transparent Data Encryption Impacts on EDB Postgres Advanced Server 15 <https://www.enterprisedb.com/blog/TDE-Postgres-Advanced-Server-15-Launch>`_ 
blog.

.. _how-does-tde-encrypt-data-1:

How does TDE encrypt data?
--------------------------

EDB TDE uses `OpenSSL <https://openssl-library.org/>`_  to encrypt data files with the AES encryption
algorithm. In Windows systems, TDE uses `OpenSSL 3 <https://docs.openssl.org/3.0/>`_  . In Linux
systems, TDE uses the OpenSSL version installed in the host operating
system. To check the installed version, run ``openssl version`` . For
more information, see the `OpenSSL documentation <https://docs.openssl.org/master/>`_  . If you’re using a custom build
not provided by the OpenSSL community, consult your vendor’s
documentation.

Starting with version 16, EDB TDE introduces the option to choose
between AES-128 and AES-256 encryption algorithms during the
initialization of the Postgres cluster. The choice between AES-128 and
AES-256 hinges on balancing performance and security requirements.
AES-128 is commonly advised for environments where performance
efficiency and lower power consumption are pivotal, making it suitable
for most applications. Conversely, AES-256 is recommended for scenarios
demanding the highest level of security, often driven by regulatory
mandates.

TDE uses AES-128-XTS or AES-256-XTS algorithms for encrypting data
files. XTS uses a second value, known as the *tweak value*, to enhance
the encryption. The XTS tweak value with TDE uses the database OID, the
relfilenode, and the block number.

For write-ahead log (WAL) files, TDE uses AES-128-CTR or AES-256-CTR,
incorporating the WAL’s log sequence number (LSN) as the counter
component.

Temporary files that are accessed by block are also encrypted using
AES-128-XTS or AES-256-XTS. Other temporary files are encrypted using
AES-128-CBC or AES-256-CBC.

How is data stored on disk with TDE?
------------------------------------

In this example, the data in the ``tbfoo`` table is encrypted. The
``pg_relation_filepath`` function locates the data file corresponding to
the ``tbfoo`` table.

.. code:: sql

   insert into tbfoo values (abc,123);
   INSERT 0 1

   select pg_relation_filepath(tbfoo);

    pg_relation_filepath
   - ---------------------
    base/5/16416

Grepping the data looking for characters doesn’t return anything.
Viewing the last five lines returns the encrypted data:

.. code:: shell

   $ hexdump -C 16416 | grep abc
   $

   $ hexdump -C 16416 | tail -5
   00001fc0  c8 0f 1d c8 9a 63 3d dc  7d 4e 68 98 b8 f2 5e 0a  |.....c=.}Nh...^.|
   00001fd0  9a eb 20 1d 59 ad be 94  6e fd d5 6e ed 0a 72 8c  |.. .Y...n..n..r.|
   00001fe0  7b 14 7f de 5b 63 e3 84  ba 6c e7 b0 a3 86 aa b9  |{...[c...l......|
   00001ff0  fe 4f 07 50 06 b7 ef 6a  cd f9 84 96 b2 4b 25 12  |.O.P...j.....K%.|
   00002000