Cryptophon

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Prototype of the cryptophone

The Cryptophon (also Cryptofon ) is an ISDN - telephone with integrated voice encryption that of Boris Floricic (also known as the "Tron") in the winter semester 1997 / 1998 as part of his thesis "entitled Implementation of encryption technology for data ISDN B-Channel ”was developed at the Technical University of Berlin . It was later to be further developed into the so-called "Cryptron", which could also have encrypted data connections.

Encryption

The Cryptophon uses the IDEA encryption algorithm for encryption . IDEA was protected by patents in the US and Europe until May 2011 . For this reason, among other things, the encryption was implemented on an exchangeable module: In this way, modules for other encryption methods could have been used later.

IDEA is a symmetrical algorithm : the complete encryption key must be known to both communication partners. A new key is required for every communication to reduce the likelihood of key compromise. A secure transmission channel is required for key exchange. This problem can be solved by securing the symmetric key by an asymmetric algorithm during the key exchange. The authenticity of the communication partner is determined based on the fingerprint of the public part of the asymmetric key. The public part of the key and its fingerprint can be transmitted via a public communication channel.

Floricic wanted to improve the cryptophone after his diploma thesis. He envisaged the RSA algorithm as an asymmetrical procedure . The key exchange should take place at the beginning of the conversation (which is still unencrypted at this point in time). After transmission, the key should be able to be compared optically or acoustically to prevent man-in-the-middle attacks . The session key transmitted in this way should then be used for the actual symmetric IDEA encryption.

technical structure

The cryptophone should be reproducible for a hobbyist . Only inexpensive and easily available components with “simple” housing types such as DIL or PLCC are therefore used on the double-sided circuit board . No unusual special devices are required for programming. The structure is divided into four subject areas:

  • The ISDN telephone board is the main board with the control and the connection to the ISDN. Main processor a is Dallas DS80C320, a fast derivative from the MCS-51 - microcontroller family . An EPROM of type 27C512 with 64 kilobyte capacity, a RAM chip of type 62C256 with 32 kilobyte capacity as data memory, a real-time clock with integrated NVRAM of type M48T08 and the ISDN controller AMD AM79C30 are connected as program memory. A text LCD and a telephone keypad are connected externally . The supply voltage is obtained from the ISDN.
DSP board
  • The ISDN DSP encryption board encrypts the data streams . It is interchangeable for improvement purposes (e.g. new algorithms ). The encryption takes place in two TI - DSPs TMS320C26. These are relatively inefficient DSPs, which Floricic removed from old modems and which at that time were inexpensive for around 33 DM (around 17 EUR). Since the performance of a single DSP was insufficient, Floricic used two of them, one each for the transmit and receive direction. The DSP code is loaded into the DSPs by the main processor.
  • The chip card contains the cryptography key. It is a simple memory card with PIN protection. Since the key is transmitted in plain text between the chip card and the main processor, there is a risk of being compromised. Floricic later wanted to use a processor card (ideally with an integrated cryptography processor) so that the cryptographic calculations could be carried out securely within it. Such cards were still very expensive back then, so Floricic could not use them.
  • The software includes both the program code for the main processor and the implementation of the IDEA for the DSPs used. Floricic developed both parts himself, they are printed in his diploma thesis. He found an elegant way to implement IDEA that saves significant computing time.

Realization and further development

By the end of 1997, Floricic had built two prototypes of the Cryptophon. Due to errors in the ISDN implementation (which was originally supposed to be realized in a second diploma thesis), these could not be operated on the public ISDN, but only on the telephone system of the TFH Berlin. The originally planned completion of the Cryptophon was not carried out because Floricic died. He had planned to develop the phone into a commercial product called "Cryptron", which could have encrypted not only telephony but also data connections. A later diploma thesis by Alexander Geraldy referred to the Cryptophon and showed that with a more efficient implementation of the IDEA algorithm developed later, the use of a single DSP would have been sufficient.

There is currently an open source project called Cryptofon , which de facto seeks to develop a new cryptophone. Codec2 is used as the speech codec , RSA - PSS or optionally AES-256 as encryption .

In September 2015, a prototype of the cryptophone from the Beuth University of Applied Sciences in Berlin was given to the Museum of Technology, also in Berlin, as a permanent loan and can be viewed there.

Cryptophone

Under the name supplemented by an 'e', ​​the Berlin company GSMK, at the same location as the Chaos Computer Club Berlin and partly operated by members of the association, has been offering mobile phones based on common hardware since 2003. The software will be modified and expanded so that encrypted audio, SMS and data communication can be operated if all the parties to the call have a GSMK device. Fixed line and satellite telephones were later added to the program.

At CeBIT 2013, Cryptophone was presented as a secure encryption method for governments, companies and in the field of intelligence (espionage). The conversations are not only encrypted tap-proof, but also concealed . The data transmission rate is only approx. 4 kbit / s and the transmission protocol used is a proprietary development by GSMK instead of the standardized SIP signaling protocol . The talks go through one of the company's own servers that are set up worldwide. It should not only remain a secret what was discussed on the phone, but also who spoke to whom. The Cryptophone found its way into the movie The Möbius Affair .

literature

  • Boris Floricic : Realization of an encryption technology for data in the ISDN B-channel . Diploma thesis at the Technical University of Applied Sciences Berlin, 1998.
  • Alexander Geraldy: Development and implementation of an encryption system for the ISDN basic connection . Diploma thesis at Saarland University, 2000 (PDF; 1.2 MB) .

Web links

Individual evidence

  1. ↑ site of the new Cryptofon project , accessed on May 15, 2013
  2. ↑ Technikmuseum Berlin: Cryptofon des Hackers Tron (prototype), 1998. Retrieved on August 18, 2017 .
  3. ↑ heise.de: Cryptophone should make mobile telephony tap-proof , November 19, 2003, accessed December 12, 2019
  4. ↑ pressebox.de: CeBIT innovation: GSMK presents mobile phone and landline encryption now also on VoIP basis , February 3, 2009, accessed December 12, 2019
  5. ↑ bz-berlin.de: The affair that came from the cell phone, October 26, 2013, accessed December 12, 2019
  6. ↑ bmbf.bund.de - securityresearchmap.de: GSMK , accessed December 12, 2019