Entries from August 2007 ↓
August 23rd, 2007 — GSM/CDMA
In an earlier post we saw how GSM networks are jammed when the SMS traffic increases. Now some smart kids can use this loop hole to attack GSM networks and cause service outage in targeted areas. This is very much similar to DOS (Denial of service) attacks in computer networks.
Even though such a possibility exists, no one can bring down the entire service down. But its very much possible to bring down certain areas of a network, lets say an area covered by a tower.
The first step is collecting mobile numbers of subscribers in that area. Attacker can use many innovative schemes to collect mobile numbers. Some methods are described here.
Once you have enough numbers in a particular region or under a tower you can start sending SMS messages to all those numbers simultaneously. An SMPP gateway is needed for this. Many companies are providing gateways.
With the help of some spoofing techniques and zombie servers an attack can be launched quite easily. Zombie servers can bypass almost all operator spam detection mechanisms. In india, bulk sms is a huge market and I dont think there are any spam detection mechanisms implemented.
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August 23rd, 2007 — GSM/CDMA
Most providers assign certain number series to certain places. All the SIMs sold at a particular location at a particular period of time can be in the same series. With a little bit of research we can identify potential numbers in a location.
Another method is to gain access to corporate databases, where customer numbers will be stored. Modern banks provide SMS alerts, and they are a good place to start looking. If you have a friend inside its really easy pulling up mobile numbers.
Another place to look is social networks, but will require some amount of programming skills. Many provide their mobile numbers in their orkut profiles. A small tool can dig out all the mobile numbers in a particular community, or a particular friends list.
Some advanced techniques would be to use a mobile worm or a virus, which can read contact lists from mobile phones and send them to a central server without the knowledge of the user. Some bluetooth worms can do this.
Once you have enough numbers with you, you need to refine the list by finding out the genuine numbers. This can be achieved by sending a test message with a fake sender ID to all the numbers and wait for delivery reports. All delivered numbers can be used for the attack.
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August 22nd, 2007 — Experiences
Finding places and roads in Ernakulam city was a tedious job for me. Asking direction while driving through traffic was the most difficult part.
While in bangalore I used to use google maps and wikimapia to find out directions, and then draw them onto a paper to avoid asking directions. But now google maps are available on mobile phones also.
Recently I installed Google maps on an N93. The app is really cool. Ive been driving around Ernakulam using this map. Almost all places are marked in the map.
Everyone with a GRPS enabled mobile phone must try out google maps mobile. Its a wonderful experience.
The next thing I want to do is to get a car pc. But To be using google maps and internet connection is needed. So Im waiting for wimax to roll out in cochin.
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August 18th, 2007 — GSM/CDMA
SMS traffic is doubling in every two years. Operators used to see this as a new revenue source. Many companies started offering services around SMS. But this explosive growth of SMS has started to created problems, mainly a degradation of the voice services.
Every operators are facing service problems during holidays and festival seasons just because of the large volume of SMS messages that are being sent. During New year almost every network will be jammed from 11:45 to 12:15. Every subsriber will be busy. This is not because everyone is calling up each other, but because the SMS traffic is blocking the voice services.
GSM networks use control channels and voice channels for handling calls and SMS messages. The control channel is used to handle SMS messages and also to setup calls. Once the call setup is finished the call proceeds using the voice channel.
Control channels have far lesser bandwidth than voice channels.
When lots of messages are pushed into the network the control channels will become busy and no control channel will be available for call setup. So all the voice services fail.
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August 17th, 2007 — Voice SMS
Voice SMS allows a subscriber to send the voice message to the other subscriber without talking to the recipient. The sender does it by dialing the recipient number in a pre-defined fashion/pre-defined by the operator. The network then routes the call to the IVR front end of the Voice SMS system. The sender then leaves a message in the Voice SMS system and hangs up the phone. The recipient is then sent an alert from the Voice SMS system about the sender’s message. The receiver of the message can then listen to the sender’s message and can also reply to the message by pressing a pre-designated numeric key and start speaking and end up by hanging up the phone. The original sender will receive an alert regarding the recipient reply and so on.
The solution shall have the features to provide:
· Message listen notification - Notification to the original sender that the intended recipient has listen to the Voice SMS end.
· Group Messaging - It should be possible to send /forward a Voice SMS to a number of subscribers.
· Message Scheduling - It should be possible to schedule the delivery of a Voice SMS at a particular time. The maximum minimum time frame for scheduling be indicated in the proposal.
· Configurable Message Storage interval - It should be possible to store a Voice SMS in the system for a BSNL configurable time period to enable a recipient retrieve/ hear the VSMS (The flexibility of the system should be highlighted in the proposal).
· Single Message Length - The typical single message length is desired as 30 seconds, however, it should be configurable by BSNL (The capability of the solution be clearly indicated in respect of this feature as minimum and maximum limit)
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