Short Message Service (sms) security solution for mobile devices

2. Asymmetric 
Cryptography 
In an asymmetric key algorithm, there are two separate keys: a public key 
and a private key. The public key is published and enables any sender to perform 
encryption; the corresponding private key is kept secret by the receiver for 
decryption. The key exchange in asymmetric encryption is much simpler because 
the public can be freely distributed. There is no requirement for separate keys for 
sub-group communications. The sender will encrypt the messages with the public 
keys of the recipients. This provides extreme flexibility when the group 
composition may change dynamically, such as in military operations.
However, the key disadvantage of asymmetric encryption is that it is 
computationally more expensive than symmetric encryption because of the long 
keys. Therefore, asymmetric encryption is seldom used in mobile devices. Even 

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on desktop computers, asymmetric encryption is used together with symmetric 
encryption for performance reasons. Section D of this Chapter attempts to shed 
some light on the resource consumption of asymmetric encryption on a modern 
Smartphone device through actual measurements. 
The more commonly used asymmetric algorithms are Rivest Shamir 
Aldelman (RSA) and the Digital Signature Algorithm (DSA). Elliptic Curve 
Cryptography (ECC) is another approach to asymmetric algorithm that allows 
shorter key lengths to be used, making it suitable for mobile device applications. 
However, ECC is still under active research and has not been widely deployed in 
systems.
For the encryption of SMS messages, the use of asymmetric encryption 
alone may be feasible due to the short message length. The measurements 
described in Section D also provide indications of the feasibility of such 
implementation.