  Selecting a library out of numerous candidates can be a laborious and
resource-intensive task. We present the $crypto_{lib}$ index, a tool for
decision-makers to choose the best fitting cryptography library for a given
context. To define our index, 15 library attributes were synthesized from
findings based on a literature review and interviews with decision-makers.
These attributes were afterwards validated and weighted via an online survey.
In order to create the index value for a given library, the individual
attributes are assessed using given evaluation criteria associated with the
respective attribute. As a proof of concept and to give a practical usage
example, the derivation of the $crypto_{lib}$ values for the libraries Bouncy
Castle and Tink are shown in detail. Overall, by tailoring the weighting of the
$crypto_{lib}$ attributes to their current use case, decision-makers are
enabled to systematically select a cryptography library fitting best to their
software project at hand in a guided, repeatable and reliable way.
