Short Message Service (sms) security solution for mobile devices

C. OBSERVATIONS 
It was observed that the signing and encryption process was fast from a 
usability perspective as compared to the time required to send the SMS. In this 
case, a 1024-bit key length was used for both encryption and signing. The 
encrypted data produced an output of 172 bytes. The signature is also 172 bytes. 
This resulted in a final message length of 346 bytes, if the two marker character 
markers are included. This means that three SMS messages are required to 
send the final message.
The waiting time for sending three SMS messages appeared very long as 
compared to the encryption processes, probably because the system status 
message is only updated when all three messages have been sent. During the 
process, nothing is seen to be happening. This may be unnerving for some users 
because the time taken to send a message is now significantly longer than 
sending a normal unencrypted message.
To improve the user interface, more feedbacks could be provided to the 
user with regard to the sending progress. The other way is to reduce the 
signature length by using a shorter key length. For example, an 840-bit key 
length will produce a 140 byte signature. This will reduce the total length of the 
message to 314 bytes, which can be sent with two SMS messages. 

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V. 
CONCLUSIONS AND RECOMMENDATIONS 
A. CONCLUSION 
In this thesis, a detailed vulnerability study was conducted on the GSM 
Network and the SMS protocol. It was concluded that application layer encryption 
is required to protect the confidentiality and integrity of SMS messages. A study 
of the different encryption schemes was conducted to understand their 
properties. Several considerations were drawn up with regard to the 
implementation of an encryption scheme on a mobile device. Of particular 
concern are the efficiency and power consumption requirements of encryption 
operations. Therefore, empirical measurements were taken to compare the 
performances of symmetric and asymmetric encryption on a modern mobile 
phone device. It was discovered that asymmetric encryption for SMS is no longer 
prohibitively expensive in terms of timing and resource consumption in a modern 
mobile device, due to advances in CPU performance for mobile devices.
A demonstration Secure Chat application was developed to validate the 
feasibility of implementing a pure asymmetric encryption solution for SMS. It was 
discovered that the overheads generated by asymmetric encryption is a key 
factor in deciding the suitability of asymmetric encryption. The long output 
lengths generated by an asymmetric encryption algorithm resulted in messages 
that are many times longer than the original message. For SMS, this is significant 
because the low bandwidth is further exacerbated.