Abstract: Key exchange methods, apparati, and computer-readable media for a cryptographic communication system. The system, which employs a novel combination of multiple channel communication, symmetric cryptography, and asymmetric cryptography, allows an entity A to bootstrap the exchange of cryptographic secrets EQB to a second entity B through an alternate communication channel 30 for the transmission of a cryptographically secure message M. The system is secure against various passive and active attacks. The encryption key transfer is briefly vulnerable to man-in-the-middle attacks, but this can be prevented in preferred embodiments.