Short Message Service (sms) security solution for mobile devices

b. 
Timing Comparison between RSA and AES 
According to Table 2, the strength of 128-bit symmetric encryption 
is close to 2048-bit asymmetric encryption. From the timing results in Table 6, it 
can be seen that the time required for RSA encryption, using a 1024-bit key 
length and a block size of 245 bytes, is approximately 30 times longer than 128-
bit AES encryption. In contrast to claims that asymmetric encryption is many 
orders of magnitudes slower than symmetric encryption, the empirical data 
showed that the actual time required for asymmetric encryption may not be 
significantly longer than symmetric encryption. In absolute terms, the difference 
is even less for smaller input lengths. Based on the results, encryption of a 100kb 
clear text using RSA with a 2048-bit key length and a 245-byte block size 
required approximately 12 seconds. For an SMS text of 160 bytes, the time 
required is significantly less, on the order of hundreds of milliseconds. The time 
required for symmetric encryption is even shorter. In terms of SMS 
communications, where the transmission of an SMS typically occurs in orders of 
seconds, the timing overhead imposed by symmetric and asymmetric encryption 
may not be perceivable by the user. 

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c. 
Power Performance Comparison between RSA and AES 
Each encryption operation using RSA 1024-bit key length 
consumes approximately 106mAH of power, when encrypting 100kb of data. As 
compared to AES encryption, the consumption for RSA encryption is about 48 
times higher. The battery capacity of the E-TEN M600 is 1440mAH. The battery 
capacities for similar devices available today are generally between 1200mAH 
and 1550mAH. This means that the E-TEN M600 will consume about 10 per cent 
of its battery power after encrypting 800 SMS messages using RSA encryption. 
The criticality of the power consumption will depend on the deployment scenario. 
If a user sends an encrypted SMS message and decrypts a SMS reply every 
minute, 800 SMS messages would be sent in 6.5 hours, and consume 10 per 
cent of the battery power. If the user is expected to be able to recharge the 
battery within this time frame, then the power consumption is not an issue.