Data encryption

Introduction

Data encryption is a new feature provided in LimeSurvey 4. It has been created to help survey administrators better cope with the new data-protection regulations adopted in different parts of the world (e.g., GDPR).

This feature permits the encryption of personal data located in the central participant database and/or survey participants table. Moreover, you can also encrypt the data you collect from your respondents if the encryption question attribute is enabled.

Please note that your data will always be visible in the LimeSurvey interface. Only the database entries get encrypted - nobody that accesses the server where you host LimeSurvey can visualize the respective data. Therefore, please pay attention to whom you provide global and survey permissions.

  Once you create encryption keys, make sure to create backups. If you lose the keys, the data will become unusable since it cannot be recovered any longer.

Settings

There are three places in LimeSurvey where data encryption settings can be set: question attributes, participant attributes, and central participant database attributes.

Question attributes

Question attribute "Encrypted" is used to enable data encryption for corresponding responses. This attribute is turned off by default. Once survey is activated, it is not possible to change this attribute.

Participant attributes

Three core attributes (firstname, lastname, and email) are always shown in the survey participants table, the encryption being turned on by default.

Each new participant attribute will have encryption turned off by default.

Encryption can be turned on or off at any moment.

Central participant database attribute management

Three core attributes (firstname, lastname and email) are always shown in the central participant database, the encryption being turned on by default.

Each new participant attribute will have encryption turned off by default.

Encryption can be turned on or off at any moment.

Advanced

Sodium library is used to provide data encryption and decryption functionality for LimeSurvey.

Sodium is a modern, easy-to-use software library for encryption, decryption, signatures, password hashing and more. It is a portable, cross-compilable, installable, packageable fork of NaCl, with a compatible API, and an extended API to improve usability even further. Its goal is to provide all of the core operations needed to build higher-level cryptographic tools.

Sodium is cross-platforms and cross-languages. It runs on a variety of compilers and operating systems, including Windows (with MinGW or Visual Studio, x86 and x86_64), iOS and Android. Javascript and WebAssembly versions are also available and are fully supported. Bindings for all common programming languages are available and well-supported.

Version 7.2.0 and newer of the PHP programming language includes the Sodium extension (referred to as ext/sodium) as a core cryptography library. Version 2 of the PHP extension in PECL is compatible with ext/sodium in PHP 7.2.

LimeSurvey uses the Sodium Compat library to bridge with different PHP versions. This library tentatively supports PHP 5.2.4 - 7.x (latest), but officially it only supports non-EOL'd versions of PHP.

Data encryption/decryption methods used in LimeSurvey are based on public-key signatures. Public and secret keys can be found in /application/config/security.php file. Keys are automatically generated on first usage of encryption feature.

  Once data encryption is turned on, data in corresponding database columns would become unreadable without decrypting them first. You should always have a backup of your encryption keys in case they get deleted. Also, once encryption keys are set, you should never change them because it would make all existing data unusable.

Partial string search won't be possible for database columns with encrypted data, only exact match search.