Key sharing has always been a complex issue. It became even more challenging for the Internet of Things (IoT), where a trusted third party for global management rarely exists. With authentication and confidentiality lacking, things resort to a leap of faith (LoF) paradigm where it is assumed that no attacker is present during the initial configuration. In this paper we focus on the Host Identity Protocol (HIP), specifically designed to provide mobility and multihoming capabilities. Although HIP is normally based on many strict security mechanisms (e.g., DNSSEC), it also provides a better than nothing opportunistic mode, based on the LoF paradigm, which is to be used when other more trusted mechanisms are not available. In this paper, we analyze different MiTM attacks which might occur under this opportunistic mode. Taking advantage of HIPs multihoming capabilities, we propose two key spraying techniques which strengthen the opportunistic modes security. The first technique spreads the four key-exchange messages among different networks, while the second spreads fractions of one of those messages. Evaluation of these techniques is provided, demonstrating the major benefit of our proposal.