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Private Number

Private Number defines a CCK field type for numbers which should be kept private, such as government-issued identification or account numbers. The module enables two of the industry standard best practices for handling confidential data: masking the number when viewed by users without view private number access permission and encrypting the number with a md5 block cipher in 128 bit CFB mode when stored.

Private Number fields can optionally have a validation pattern, which will both validate input and provide a human-readable form of the pattern for field descriptions and error messages. The module exposes a hook for private number access to be integrated with contributed or custom modules.

2010-04-07: 5.x will be supported with bug fixes only. A demo of Private Number can be viewed at

CCK Content module

Related Modules

  • Secure Pages
    private information should also be encrypted during transmission via SSL.
  • GnuPG
    OpenPGP API for encrypting emails.
  • encrypted_text
    CCK widget that encrypts fields with MySQL's AES_ENCRYPT() function, but does not handle access for display.


  • Access permissions
    Private Number introduces two access permissions, view private number and view own private number. Private numbers are displayed as 'Ending in 123' for users without this permission. The number of digits displayed can be changed on a per field basis with Display fields settings.
  • md5 block cipher encryption
    Private Number data can optionally be is stored in the database with md5 block cipher encryption. This is recommended to help thwart identity theft if access to your database becomes compromised. A unique site key must be set in either the $conf array of settings.php or in an external file outside of docroot. See Key Management below.
  • Validation patterns
    Validation patterns can optionally be added for any Private Number field. In addition, validation patterns will (usually) output a human-readable form for field descriptions and error messages. The human regex error messages can be disabled at the field level. See Validation Patterns below.
  • Third-party module integration
    Private Number can be integrated with contributed or custom modules by implementing hook_private_number_access() to enable view or edit access. See Developers below.


  1. install module: copy private_number directory and all its contents to your modules directory
  2. enable module: admin/build/modules
  3. configure module: admin/settings/private_number (5.x only)
  4. configure access permissions: admin/user/permissions#module-private_number
  5. set a unique site key before using module: see Key Management below

Download package and report bugs, feature requests, or submit a patch from the project page on the Drupal web site.

Key Management
Private Number implements md5 block cipher encryption which requires a unique cipher (or site) key. Note that changing the key will make previously stored Private Numbers unreadable! By default, a site key is set in the $conf array of settings.php with the $conf['private_number_key'] variable.

For more security, use the site key path and create a text file named private_number.key one level above the Drupal installation (e.g. above www). Place your key on the first line of that file. Change permissions on the file to 0444. The file can be moved to another location or name changed by altering the $conf['private_number_key_file'] variable.

Validation Patterns
Private Number validation patterns are passed through preg_match with start and end of string delimiters automatically appended. It is beyond the scope of the module to provide support for crafting your own regular expressions, but there are numerous resources on the subject (a particularly good one is

Examples of common validation patterns:

For a U.S. telephone number, the pattern would be:
$pattern='\(\d{3}\) \d{3}\-\d{4}';

which would output in human-readable form as:
(999) 999-9999

For a U.S. social security number, the pattern would be:

which would output in human-readable form as:

We chose to use phrases for quantifiers because it provided more understandable output than the 9 notation, but can quickly get cumbersome when more than one quantifier is used in an expression.

\d? 0 or 1 digit
\d+ 1 or more digits
\d* 0 or more digits
\d{1,3} 1 to 3 digits

Be sure to escape meta characters in your validation pattern. For more information on preg_match, visit this page:

Private Number can be integrated with contributed or custom modules by implementing hook_private_number_access() to enable view or edit access.

// View all friend's private number fields (in pseudo code).
function example_private_number_access($op, $node, $field, $account) {
  if ($op == 'view') {
    if ($account->uid IS FRIEND OF $node->uid) return TRUE;

// Enable users in role ID 3 to edit a private number field named field_secret.
function example_private_number_access($op, $node, $field, $account) {
  if ($op == 'edit' && $field['field_name'] == 'field_secret') {
    if (in_array(3, array_keys($account->roles))) return TRUE;

Module development sponsored by LifeWire, a service of, a part of The New York Times Company.

Project information