Cell phone technical question

ve3opc · Aug 18, 2016

Understanding fully as to the legalities of receiving such transmissions but was simply curious...Is just a question as to these bands being blocked or are current scanners capable of even deciphering such transmissions....I read they use TDMA and current scanners can decrypt TDMA so that being the case if some one was bent on listening to them a converter box could be attached to the front end ? Yes /No ?

nd5y · Aug 18, 2016

No. GSM and TDMA-136 are totally different and the bandwidth is much wider than P25 phase II and DMR.

kayn1n32008 · Aug 18, 2016

ve3opc said:
?..TDMA and current scanners can decrypt TDMA so that being the case if some one was bent on listening to them a converter box could be attached to the front end ?

The latest scanners do not 'decrypt' TDMA transmissions because they have no encryption capabilities. Scanners decode TDMA transmissions, only if they are not encrypted.

ve3opc said:
Yes /No ?

No. While they both use TDMA, the way the data is applied is not in any way similar.

IAmSixNine · Aug 18, 2016

Also to add to it scanners dont Decrypt anything. When they listen to a DMR channel its simply a digitial format but its not encrypted. You can overlay encryption with it then the scanner would not be able to pick it up.
They can monitor and decode the digital transmission as long as its not encrypted.

kayn1n32008 · Aug 18, 2016

kayn1n32008 said:
The latest scanners do not 'decrypt' TDMA transmissions because they have no encryption capabilities. Scanners decode TDMA transmissions, only if they are not encrypted.

No. While they both use TDMA, the way the data is applied is not in any way similar.

IAmSixNine said:
Also to add to it scanners dont Decrypt anything. When they listen to a DMR channel its simply a digitial format but its not encrypted. You can overlay encryption with it then the scanner would not be able to pick it up.
They can monitor and decode the digital transmission as long as its not encrypted.

Is that not almost exactly what I just stated? FYI TDMA is not limited to DMR...

W8RMH · Aug 18, 2016

Look at the post times, you both were probably typing at the same time.

IAmSixNine · Aug 18, 2016

W8RMH said:
Look at the post times, you both were probably typing at the same time.

He is correct, i loaded up a few pages to view and replied as soon as i submitted mine yours popped up above me. So had i refreshed the page yours would have been there.. I thought about a quick edit. Guess i should have.

K5MPH · Aug 18, 2016

TDMA for cell phones have Encryption.....

UPMan · Aug 18, 2016

TDMA is not a protocol. It is a method. P25, DMR, ProVoice, etc, are protocols (that all happen to use variations of the DVSI codecs) that some scanners can receive and decode. P25 and DMR happen to use TDMA. Cellular (mobile) telephony uses completely different protocols and codecs and are also encrypted. The current regulation requiring certain frequencies be blocked is still in effect has been entirely obsoleted by technology. However, scanner manufacturers must still comply with those regulations which cost scanner makers (and their customers) quite a bit of money.

talkpair · Aug 18, 2016

Here in the US, I believe the blocking of frequencies on scanners dates back to the era when cell phones were analog. (AMPS)

At one time, I had one of the unblocked scanners. It was pretty much impossible to follow a conversation because of the frequent handoffs between towers. Unlike following a trunked radio system, there was nothing built in to the scanner that allowed a person to do anything useful with it anyway. Even if you managed to follow a call to a weaker site, the chances were good that another site would reuse that same frequency and drop a different call on top of the one you were listening to.

Because air time and roaming charges were pricey at the time, the people that had cell phones didn't use them as heavily as they do now.

Darkstar350 · Aug 20, 2016

I thought cells used CDMA - not Tdma...

As far as monitoring cellphone calls - it wouldnt suprise me if the technology is out there but very illegal for "civilians" and it would probobly involve professional equipment such as a spectrum analyzer which is in excess of about $15,000 usd...

kayn1n32008 · Aug 20, 2016

Darkstar350 said:
I thought cells used CDMA - not Tdma...

Some older formats used TDMA.

SCPD · Aug 20, 2016

GSM/Edge is TDMA. IDEN is TDMA. Some of the newer LTE bands are a form of TDMA.

Sent from my SM-G900W8 using Tapatalk

mikewazowski · Aug 20, 2016

bidulock said:
GSM/Edge is TDMA. IDEN is TDMA. Some of the newer LTE bands are a form of TDMA.

Sent from my SM-G900W8 using Tapatalk

LTE-TDD.

Rred · Aug 20, 2016

"GSM/Edge is TDMA"
I wouldn't call it that simple, since AT&T formally "dropped TDMA in favor of GSM" years ago. And Verizon dropped CDMA "in favor of CDMA2000" around the same time.
Cellco engineers have also more recently said that 4G LTE (not to be confused with 4G, which is simply "enhanced" HSDPA aka HSDPA+ in the US) can be considered both CDMA and TDMA as it has some of the properties of each.
And FWIW the simplest way to listen in on cell phones is to deploy a picocell (aka femtocell) as a "man in the middle" which will often be able to decrypt signals the same way the legitimate towers do. Law enforcement does this routinely.

sopranosno1 · Aug 22, 2016

Isnt it stingray what the feds and locals ade using?

SCPD · Aug 22, 2016

Sting Ray

Yes it is.

Rred · Aug 23, 2016

Stingray is one of the "code" names for one specific manufacturer's product that does this, yes.

IIRC there have been some much cheaper and smaller DIYs demonstrated at DefCon and the Black Hat conferences in previous years, proving the same point. The cellular system was never designed to address the problem of man-in-the-middle attacks, that's a system weakness.

Which is one reason why Obama wasn't allowed to use his cell phone (initially) and why end-to-end private encryption software has been so common for cell phones. It may not stop the NSA, but it certainly will slow down a lot of people.

RayAir · Sep 4, 2016

Google "femtocell hack" and go on YT and search "GSM hack".

The femtocells were sold or given to cellular customers to boost cell phone signal strength in low signal areas. It was discovered these devices could be modified to act as a "poor man's IMSI catcher" or Stingray device.

The GSM hack was done using SDR and a program ran on Linux. The voice and text were encrypted but the algorithm was fairly weak and defeated from what I've read. I'm not sure if it was a MITM or brute force attack.

I'm sure the info is out there for those curious.

tj20 · Oct 25, 2016

UPMan said:
TDMA is not a protocol. It is a method. P25, DMR, ProVoice, etc, are protocols (that all happen to use variations of the DVSI codecs) that some scanners can receive and decode. P25 and DMR happen to use TDMA. Cellular (mobile) telephony uses completely different protocols and codecs and are also encrypted. The current regulation requiring certain frequencies be blocked is still in effect has been entirely obsoleted by technology. However, scanner manufacturers must still comply with those regulations which cost scanner makers (and their customers) quite a bit of money.

It is funny that those frequencies were blocked because back in the day my bct 7 could pick up analog cell phone "images" (I don't know the correct term) in the 900 mhz. I heard quite a few intersting calls, like a couple having phone sex lol.

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