Technology is described for two parties, by leveraging previously established secure connections with third parties, to obtain a shared secret for generating a secure connection with each other in a way that reduces vulnerability to man-in-the-middle attacks. In some examples, the technology can include generating a session identifier; coordinating use of the session identifier by the two parties; finding an available secure communication channel to a third party; transmitting the session identifier to the third party via the available secure communication channel; receiving, via the available secure communication channel, a third party identifier and a session identifier-specific secret; sharing information about the received third party identifier; determining that the received third party identifier matches a third party identifier received by the second party; and using the session identifier-specific secret received with the matching third party identifier to generate a cryptographic key to secure communication between the two parties.