  The massive deployment of IoT devices being utilized by home automation,
industrial and military scenarios demands for high security and privacy
standards to be achieved through innovative solutions. This paper proposes
KaFHCa, a crypto-less protocol that generates shared secret keys by combining
random frequency hopping collisions and source indistinguishability
independently of the radio channel status. While other solutions tie the secret
bit rate generation to the current radio channel conditions, thus becoming
unpractical in static environments, KaFHCa guarantees almost the same secret
bitrate independently of the channel conditions. KaFHCa generates shared
secrets through random collisions of the transmitter and the receiver in the
radio spectrum, and leverages on the fading phenomena to achieve source
indistinguishability, thus preventing unauthorized eavesdroppers from inferring
the key. The proposed solution is (almost) independent of the adversary
position, works under the conservative assumption of channel fading ({\sigma} =
8dB), and is capable of generating a secret key of 128 bits with less than 564
transmissions.
