I would like to know if there are only the Security GEs exposed in the Fiware catalogue. Specifically, I am interested in one component that can do cryptographic functions, like generate and provide key pairs, encrypt, decrypt, etc.
If the answer is no, how can I suggest/implement one GE for this purpose?
The Security GE implementations in FIWARE focus mostly on authentication/authorization and risk analysis. So I would say, no, there are no GEs specifically offering the functionality you are looking for.
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By the way, a component which provides a set of cryptographic functions would probably be considered as a FIWARE Tool but not a GE. You can take a look at the existing FIWARE Tools, here.