Cryptophon
"Cryptophon" (or "Cryptofon") was the name Floricic chose for his prototype of an ISDN telephone with integrated voice encryption. It was created in the winter term 1997–1998 as part of his diploma thesis, titled "Realisierung einer Verschlüsselungstechnik für Daten im ISDN B-Kanal" (German, meaning, "Implementation of Cryptography for Data contained in the ISDN Bearer channel"), at the Technische Fachhochschule Berlin. Floricic focused on making the Cryptophon cheap and easy to build for hobbyists. The phone encrypts telephone calls using the symmetric encryption algorithm IDEA. As IDEA is patented, the cipher was implemented on a replaceable daughter module which would have allowed the user to exchange IDEA for another (probably patent-unencumbered) algorithm. In addition, the system was about to be supplemented with a key exchange protocol based on the asymmetric algorithm RSA in order to achieve security against compromised remote stations.
The Cryptophon is built on the foundation of an 8051 compatible microprocessor which controls the whole system and peripherals (e.g. ISDN controller, keypad and display). For the cryptography Floricic used cheap DSPs from Texas Instruments which he scrapped out of old computer modems, but which could also be bought at affordable prices. As this type of DSP is not powerful enough for the cryptography algorithm chosen, Floricic used two of them for the Cryptophon – one for sending and one for receiving. He planned to extend the phone so it would also be possible to encrypt data-connections. Floricic developed both the operating software of the phone as well as the cryptography implementation in the DSPs. He found a new way to implement IDEA to save significant processing time.
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