  Certificates ensure the authenticity of users' public keys, however their
overhead (e.g., certificate chains) might be too costly for some IoT systems
like aerial drones. Certificate-free cryptosystems, like identity-based and
certificateless systems, lift the burden of certificates and could be a
suitable alternative for such IoTs. However, despite their merits, there is a
research gap in achieving compatible identity-based and certificateless systems
to allow users from different domains (identity-based or certificateless) to
communicate seamlessly. Moreover, more efficient constructions can enable their
adoption in resource-limited IoTs.
  In this work, we propose new identity-based and certificateless cryptosystems
that provide such compatibility and efficiency. This feature is beneficial for
heterogeneous IoT settings (e.g., commercial aerial drones), where different
levels of trust/control is assumed on the trusted third party. Our schemes are
more communication efficient than their public key based counterparts, as they
do not need certificate processing. Our experimental analysis on both commodity
and embedded IoT devices show that, only with the cost of having a larger
system public key, our cryptosystems are more computation and communication
efficient than their certificate-free counterparts. We prove the security of
our schemes (in the random oracle model) and open-source our cryptographic
framework for public testing/adoption.
