Put on your Masks !

The main idea of this extension is to offer anonymization by design.

The data masking rules should be written by the people who develop the application because they have the best knowledge of how the data model works. Therefore masking rules must be implemented directly inside the database schema.

This allows to mask the data directly inside the PostgreSQL instance without using an external tool and thus limiting the exposure and the risks of data leak.

The data masking rules are declared simply by using security labels:

CREATE TABLE player( id SERIAL, name TEXT, points INT);

INSERT INTO player VALUES
  ( 1, 'Kareem Abdul-Jabbar', 38387),
  ( 5, 'Michael Jordan', 32292 );

SECURITY LABEL FOR anon ON COLUMN player.name
  IS 'MASKED WITH FUNCTION anon.fake_last_name()';

SECURITY LABEL FOR anon ON COLUMN player.id
  IS 'MASKED WITH VALUE NULL';

Escaping String literals

As you may have noticed the masking rule definitions are placed between single quotes. Therefore if you need to use a string inside a masking rule, you need to use C-Style escapes like this:

SECURITY LABEL FOR anon ON COLUMN player.name
  IS E'MASKED WITH VALUE \'CONFIDENTIAL\'';

Or use dollar quoting which is easier to read:

SECURITY LABEL FOR anon ON COLUMN player.name
  IS 'MASKED WITH VALUE $$CONFIDENTIAL$$';

Listing masking rules

To display all the masking rules declared in the current database, check out the anon.pg_masking_rules:

SELECT * FROM anon.pg_masking_rules;

Debugging masking rules

When an error occurs to due a wrong masking rule, you can get more detailed information about the problem by setting client_min_messages to DEBUG and you will get useful details

postgres=# SET client_min_messages=DEBUG;
SET
postgres=# SELECT anon.anonymize_database();
DEBUG:  Anonymize table public.bar with firstname = anon.fake_first_name()
DEBUG:  Anonymize table public.foo with id = NULL
ERROR:  Cannot mask a "NOT NULL" column with a NULL value
HINT:  If privacy_by_design is enabled, add a default value to the column
CONTEXT:  PL/pgSQL function anon.anonymize_table(regclass) line 47 at RAISE
SQL function "anonymize_database" statement 1

Removing a masking rule

You can simply erase a masking rule like this:

SECURITY LABEL FOR anon ON COLUMN player.name IS NULL;

To remove all rules at once, you can use:

SELECT anon.remove_masks_for_all_columns();

Limitations

  • The maximum length of a masking rule is 1024 characters. If you need more, you should probably write a dedicated masking function.

  • The masking rules are NOT INHERITED ! If you have split a table into multiple partitions, you need to declare the masking rules for each partition.

Declaring Rules with COMMENTs is deprecated.

Previous version of the extension allowed users to declare masking rules using the COMMENT syntax.

This is not supported any more. SECURITY LABELS are now the only way to declare rules.