@cagatay-Baser On the page http://repo.onion.io/omega2/packages/base/ you can see that there's the libmbedtls package. But that seems to be only the runtime and not the dev files?

If you just want to develop a program using the mbedTLS lib, you'd just develop it on a cross-compiling machine, dynamically link it against libmbedcrypto, libmbedx509 and libmbedtls, install the run-time on the Omega2 via opkg install libmedtls and transfer and run your cross-compiled binary there.

Depending on configuration changes (config.h) and version incompatibilities (above is libmbedtls_2.5.1-1) however it might be just wiser to cross-compile everything and transfer the cross-compile mbedtls libraries with the program together in one go. Or just link it statically.