The Hardware Side of Cryptography

19 December 2008

Final Project Plan

Filed under: encryption — Tags: , , , , , , , — edipermadi @ 9:24 am

Yesterday, i was thinking about my final project will be started on January 2009, perhaps up to June 2009. A great chance that drives me to learn more and more. The topics is around applied embedded cryptography, probably PSTN cryptophone .

A PSTN cryptophone is basically a device that interface telephone line. The device will encrypt and decrypt voice using RC4 stream cipher combined with Diffie Hellman Key Exchange algorithm. In addition i’m planning to use environment driven Pseudo Random Number Generator that combines generated random number and noise captured from environment .

I realized that PICmicro microcontrollers are no longer sufficient to fulfill my needs. I am supposed to use another microcontroller. A great candidate is AVR, a cool, fancy, fast, and single cycled machine. Far away before, i was motivated my self to grab the sense of using AVR by on hand practices, and it works, thanks God. Now i’m able to program AVR, i’m pursuing my dream to create my own hand made PSTN cryptophone, wish me luck .

The motivation of this idea comes from the needs of privacy over unsecure PSTN (Public Switched Telephone Number) which is secure enough and affodable for public use. PSTN is said to be unsecure, since it was easy to tap and intecept any conversation without any hard effort. Can you imagine if someone is passing his sensitive data through telephone line and a bad guy is tapping the wire and steal that informations? Of course, that could be a horrible things to be heard .

If possible, i will publish this project as a book and ebook. Yeah, i had a dream to publish a book which is cool, original, exceptional and high tech. Hopefully everything is running well .


  1. Hehehe dont forget to make it easily understood by newbie😀. Good luck Ed.

    Comment by fandigunawan — 26 December 2008 @ 8:11 pm

    • thank you for notifying me ^_^. Wish all the best for us

      Comment by edipermadi — 30 December 2008 @ 10:47 am

  2. sip2… ditunggu perkembangan selanjutnya ya!🙂

    Comment by zakimath — 27 December 2008 @ 2:02 pm

    • Mohon doanya mas zaky, semoga semuanya lancar, amiin..🙂

      Comment by edipermadi — 30 December 2008 @ 10:26 am

  3. hehehe di biar ntar anggota Hewan DPR bisa aman di klo mo korupsi nelponnya lewat telpon biasa aja, gk usah hape2an…


    Comment by Ferdy — 30 December 2008 @ 5:55 pm

    • Huss, ini buat transaksi banking mas, bukan buat yang gak bener🙂

      nanti bisa ditangkap polisi gara2 dituduh jadi fasilitator korupsi


      Comment by edipermadi — 30 December 2008 @ 6:01 pm

  4. @Ferdy: hahaha… yg namanya teknologi memang seperti dua mata pisau, bisa digunakan untuk kebaikan dan juga kejahatan…🙂

    Comment by zakimath — 5 January 2009 @ 7:48 pm

    • @zakimath :
      hehe bener mas, setuju bangetz. ya itulah teknologi, apapun itu tergantung penggunanya :p

      Comment by edipermadi — 6 January 2009 @ 8:49 am

  5. Hi, Edi,
    Your Secure PSTN phone is an interesting project. But there is a short distance between the normal telephone POTS and the nearest digitized central office switch that uses analogue signal.
    So are you going to do the encryption on the analogue basis or after digitized? In short, I have some questions for you:
    1). Any Vocodec to be used?
    2). If analogue Interface is the entrance of your payload, what is the MODEM scheme to be used?


    Comment by Oliver — 12 January 2009 @ 10:58 am

    • @oliver :
      thank you for visiting my blog. I will not use any vocodec, it’s just as simple as ADPCM. for analog interfacing purpose, i’ll use external modem instead, and interface it using AT command. all encryption are done after voice has been digitized. Dude, if you have better way to do it, please inform me.

      Comment by edipermadi — 12 January 2009 @ 11:11 am

  6. Nice Idea…!!

    Kemarin temen gw bikin proposal TA tentang enkripsi suara pada jaringan telepon pake algoritma Grain-128 ditolak.

    BTW pake AVR berapa? ATmega32? Kebetulan TA gw juga pake AVR ATmega32, algoritmanya RC4. Bikin dongle enkripsi sekaligus pengaman buat aplikasi FTP.

    O iya. udah kadaluarsa. pindah ke Tapi ga nulis tentang kripto coz dah eneg kripto disini nih.

    Comment by Bayu S — 15 January 2009 @ 11:08 am

    • @bayu : thanks dah ngunjungin blog gw.
      haha.. btw kenapa ditolak tuh, padahal algo grain lumayan baru. apa idenya dah garing kali ya, renyah gurih gitu hehe…

      rencananya per unit pake 2 buah ATMega32. satu buat pseudo random number generator plus crypto engine. yang satu lagi buat event & user interface handler.

      wah dongle enkripsi keren juga tuh,, ampun DJ…

      Thanks update blognya, nanti biar gw update link nya.

      Comment by edipermadi — 15 January 2009 @ 11:23 am

  7. Dia mau bikin secara hardware semua. Bayangannya dia suara->sample and hold->ADC->Enkripsi->DAC->PSTN.
    Ditolak karena pengujinya ngerasa ga bakalan cukup waktu 5 bulan buat ngerjain itu.
    Apalagi semua based on hardware.
    Akhirnya dia bikin dongle pengaman buat BIOS.
    Anyway gut luck buat Skripsinya.
    Kapan mulai nulis.

    Comment by Bayu S — 17 January 2009 @ 8:00 am

    • @bayu :
      iya sih emang ribet kerjaan nya, tapi bagian DAC handlingnya gw simplify pake modem eksternal, jadi tinggal ngurusin AT command aja sama protocol aja. semoga lancar deh… amiin

      Comment by edipermadi — 18 January 2009 @ 4:19 pm

  8. @bayu & edi

    Wakakakak gw pikir kenapa skripsinya ditolak padahal gw lihat sih keren, eh gak tahunya emang gara2 waktunya gak cukup. kalau gitu berarti dosennya gak pengen nahan mahasiswa lama2. Berjuang bro.

    Comment by Fandi Gunawan — 23 January 2009 @ 8:40 pm

    • @fandi gunawan : minta doanya aja bro, semoga semuanya terlaksana dengan lancar, amiin…

      Comment by edipermadi — 29 January 2009 @ 9:31 am

  9. Hi

    Check the Siemens SL965 PSTN crpyto phone. It uses some of the algos you mention – Diffie (3072 bit key) and 256 bit AES. The crypto takes probably less than 7MIPS but getting an embedded PSTN modem working over international line networks (for digitsed voice) means using a good codec under 9kbps compression and the modem / line / echo cancel is going ot be the challenge – I opened one up and it uses a TI DSP with a Sprint modem in it. Just in case you are interested….might I suggested something a little simpler and perhaps even more useful ? taking your cool AES stream cifer for PIC – why don’t you build an in line PC keyboard “dongle” (a bit like those keylogger things) except it converts all your ascii to hex, snips it into 128 (or 256) chunks and encyrpts it. You could use that eaisly for all instant messaging, chat rooms, emails, SMS….the person would just have to figure a one time way of getting thier key to the other side (better on a smart card) so you could have the little donlge linked to your smart card interface (cut and paste the hex key or send via PGP etc. Would be a hot project…!

    Comment by baz — 8 May 2009 @ 6:13 pm

    • @baz

      Hi, I’m almost finish my hardware. It does not use a sophisticated voice codec, its just as simple as ADPCM. Thank you for your suggestion. i’ll try to think about it. by the way, can you explain me more about Siemens SL965 PSTN crpyto phone, since i dont have it🙂

      Comment by edipermadi — 11 May 2009 @ 11:08 am

  10. I don’t know much more about it, it seems to be the MMS cordless phone they sold before and then they used the dsp in there for crypto instead of pictures.

    A recent telephone line design you can find here using AVR:

    You will find the download file of firmware and source here
    on this page:

    look for

    and replace the encrpytion with your AES stream .O)

    good luck

    Comment by Baz — 16 May 2009 @ 9:15 pm


    ok I found the phone (above)

    Comment by Baz — 16 May 2009 @ 9:19 pm

  12. let me know how it goes – new email :O)

    Comment by Baz — 16 May 2009 @ 9:24 pm

  13. try:

    software here:

    look for

    use AES stream instead .O)

    Comment by Baz — 16 May 2009 @ 9:26 pm

    • @baz:
      thank you very much for your hints to the software. At this moment, i’ll just implement the cipher using RC4. Gradually i’ll update the firmware and replace the cipher by AES configured as stream cipher.

      Again, thank you very much

      Comment by edipermadi — 18 May 2009 @ 9:35 am

  14. Thank you for best information.

    Comment by buy cordless phone — 23 June 2009 @ 9:02 pm

  15. hi..i am doing my fyp on encryption and decryption of voice for a telephone line..can somebody help me regarding this.

    Comment by umair — 8 December 2009 @ 10:31 pm

  16. @eddi buddy can u help me out on hardware..

    Comment by umair — 8 December 2009 @ 10:42 pm

    • @umair
      Hello, i probably can help you in hardware. could you please tell me the technical specification of your project and send it to my email.

      Comment by edipermadi — 9 December 2009 @ 7:57 am

  17. whats ur email eddi??

    Comment by umair — 9 December 2009 @ 8:30 pm

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