Web Application Security
SMS protection Oct 21 2011 05:57PM
Marcel Tudorache (marceltudorache yahoo com) (4 replies)
Re: SMS protection Oct 25 2011 08:45PM
Robin Wood (robin digininja org)
RE: SMS protection Oct 25 2011 05:26PM
Jesse Mundis (jesse voltage com)
Hi Marcel.

For any practical purpose, I'd have to suggest your assumptions are invalid. In any sort of real world use, you will have to assume the user can be, or has already been tricked into installing some sort of app that requested the ability to read SMS messages. Once that happens, your scheme is blown. I'd never use such a system for anything but trivial, low-value, game-sign-ups and such. Certainly not banking, or anything banking-like.

However, taking your assumptions as valid, it's still a bad idea. SMS have a number of weaknesses from a security standpoint. See http://en.wikipedia.org/wiki/SMS#Vulnerabilities Anyone with the right equipment should be able to pluck the contents of all the SMS texts flying past them out of the air easily.

So, while it might be difficult (with your assumptions) for any specific attacker to intercept any specific target, it should be easy for an arbitrary attacker to listen in on an arbitrary target.

If your task is to secure anything like banking, I wouldn't depend on SMS for my security if I were you.

Jesse Mundis
I do not speak for my employer.

-----Original Message-----
From: listbounce (at) securityfocus (dot) com [email concealed] [mailto:listbounce (at) securityfocus (dot) com [email concealed]] On Behalf Of Marcel Tudorache
Sent: Friday, October 21, 2011 10:58 AM
To: webappsec (at) securityfocus (dot) com [email concealed]
Subject: SMS protection

Hi,

I was wondering how secure is an SMS to be used as authentication/transaction signing means for an application similar with online banking.

To make the analysis more targeted the following assumptions are made:
- I understand that the new smartphones can get viruses, but I would like to analyse the simple case where we assume that the user does his due dilligence and either does not navigate on the internet or navigates on limited number of trusted websites, so the assumption is that the user does not have an trojan/malware/virus on the smartphone.
-bluetooth is off
- Wifi off...
- the attacker does not have phisycal access to the mobile phone

I think that the SIM card is pretty difficult to be hacked, from my smart card experience(limited), I would assume that before allowing the access to the network of a cloned SIM card the operator might validate some signature of the sim-card (I guess that when the operator issues SIM cards they sign them with their private key... or a similar process).

The question is merely about the intrinsic security of receiving an SMS, and how easy would be for an attacker to read the SMS of somebody else taking into account the above assumptions.

I think it should be pretty secure, what do you think?

Thank you very much,
Marcel

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[ reply ]
Re: SMS protection Oct 25 2011 02:07AM
Francois Yang (francois y gmail com)
Re: SMS protection Oct 25 2011 12:11AM
Fyodor (fygrave gmail com) (1 replies)
Re: SMS protection Oct 29 2011 10:55PM
Marcel Tudorache (marceltudorache yahoo com)


 

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