Short Message Service (sms) security solution for mobile devices

C. KEY 
CONSIDERATIONS 
There are several key considerations when choosing a suitable encryption 
scheme for an application. The most important consideration is the deployment 
scenario for the use of the encryption scheme. The value of the information to be 
protected, the expected threats and the physical disposition of the users are key 
considerations when deciding on a suitable encryption scheme. However, due to 
the varied nature of the deployment scenarios, these factors are not discussed 
here. This Section assumes that the risk assessment has already been 
conducted and SMS is assessed to be a viable communications channel based 
on the security policy. The rest of this Section highlights the important 
considerations when choosing an encryption scheme for mobile devices. 

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1. Algorithm 
Strength 
The strength of an algorithm is derived from the mathematical properties 
of the algorithm. For example, RSA derives its strength from the difficulty of 
factoring large numbers. If a method that radically speeds up the factoring of 
large numbers is discovered, the RSA algorithm can be broken [29]. This is the 
fundamental assumption behind the use of algorithms. Since, nobody can predict 
the breakthroughs in mathematical methods, developers writing applications that 
use encryption must be mindful of the assumptions behind the algorithms and be 
updated of the latest developments. 
While no one can be absolutely certain about the strength of an algorithm, 
it is generally accepted that an algorithm that has been subjected to public peer 
review is more secure, except against the most determined and resource rich 
state agencies [29]. The GSM A5 encryption algorithm is an example of a failure 
in encryption algorithm that has been developed in secrecy. Once the closed 
algorithms are leaked or reverse engineered, they will be crypto-analyzed. 
Therefore, secret algorithms only provide added security if they are as closely 
guarded as the secrets that they are meant to protect, and the algorithm is 
designed by cryptography experts who know exactly what they are doing, and 
the algorithm has gone through some internal, independent reviews.