eID clients are the central software (middleware) that facilitates the eID function on users' systems. They handle the encrypted communication that takes place between users' eID cards, eID servers, and eID applications.

In this context, a distinction is made between two variants: A conventional eID client (full client) is a program or app with a corresponding user interface that can run on its own on a user's system. An eID kernel or eID core, meanwhile, does not have its own user interface. This variant is particularly suitable for integrating the eID function directly into mobile apps (as an integrated client).

Framework conditions

The technical basis for eID clients is provided by the functional specification found in part one of Technical Guideline BSI TR-03124. Part two describes the tests that can be performed to determine the extent to which eID clients conform to this specification. These conformity tests also ensure the interoperability of eID clients with other eID components.

To facilitate such tests, a tool called eID-Client-Testbed was created on behalf of the BSI. This open-source program is available free of charge in the GitHub repository eID-Testbeds.

Development system

As a rule, eID client developers are advised to also provide versions of their eID clients that run properly in the development system.

Test system

Technical Guideline BSI TR-03124 recommends that eID client developers provide a test version for use in the test system. A test version of this kind usually offers advanced options for error output and analysis (read: a developer mode). To ensure interoperability with other eID components, a certified (or at least conformity-tested) eID client should be used for testing purposes.

Active system

Publicly available eID clients can be downloaded and used by any user. The BSI recommends the use of a certified eID client. A list of all the certified eID clients can be found on the BSI website under Certified Products -- eID clients.