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PACTOR - The mediator

It was during summer 02001. I went to see my sister that was working for an NGO in Ikonda, Tanzania, there, at the Wakinga Mountains.

At that time I was an IT student and got quite surprised about how they were able to receive emails in a place where there were not even telephone lines (do not talk about cell phones).

She explained me that they were using a device called PACTOR, some kind of modem to transmitt data over RF. But nobody in Ikonda was able to explain me how it worked exactly. Somehow it came to my mind the other day and I wondered about the security of the system. How secure could it be if RF signals are, by definition, broadcasted? For sure there was a method, so I decided to do some research.

PACTOR systems are an evolution of AMTOR and Packet Radio. They use Frequency Shift Keyed modulation (FSK) with CRC error correction and automatic repeat request (ARQ) to stablish a reliable link-to-link connection between two radio stations even though they can eventually, use a data broadcast mode if necessary.

It is mainly used by Marine operators and amateur radio operators in remote locations, as my sister was. Besides the computer, the PACTOR modem and the radio, it is necessary to contact a service provider to gain access to email (the most popular use case) or any other data service. There are several companies providing this all around the globe.

Don't forget to send me an email!

PACTOR has evolved during the last two decades. PACTOR I (1989) has the worst performance of the family, but still in use because it is an open technology and the most economic. PACTOR II (1995) and PACTOR III (2002) are great improvements on the same idea and much more efficient, but they are still propietary technologies. It is possible to upgrade from II to III just by a software update. All PACTOR systems are compatible and, if someone is interested, I have found a very good description and comparison between all types.

So, what about security?

If a user is concerned about privacy in their emails or other data, he can use two main methods:
· To stablish encryption in the link using the modem's firmware. This method is not so widely used, as it requires more resources.
· Use PGP or other encryption methods at both ends to protect the information itself.

Nothing we could not have thought about, right? But learnt some things in between to share with you. ;)

Luis Tarrafeta
S21sec labs

Note: Great thanks to Martin Clas (SCS) for his kind answers to my questions.

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