Short Message Service (sms) security solution for mobile devices

4. Power 
Consumption 
Power is a key constraint for mobile devices. Therefore, most mobile 
devices have extensive power management features to conserve battery power 
as much as possible. Encryption operations are computationally intensive. 
Therefore, the power consumption of encryption operations must be taken into 
account when deciding on an encryption scheme. Section D of this Chapter 
describes an experiment that was conducted to measure the power consumption 
of different encryption operations.
Although the power consumption associated with each encryption 
operation may be small, encryption operations occurs very frequently in network 
encryption. For example, in Internet Protocol Security (IPSec), every Internet 
Protocol (IP) packet is signed and encrypted. This translates to three encryption 
operations per IP packet that is transmitted or received: one for confidentiality 
protection, one for hashing, and one for digital signature. The cumulative 
consumption can be quite significant, depending on the amount of network traffic.
5. Speed 
The speed and efficiency of the encryption operation has a direct impact 
on the network bandwidth and the usability of the system. Saltzer and Schroeder 
[31] wrote about psychological acceptability as one of the security design 
principles. Security solutions that are implemented must be usable and as 

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transparent to the user as possible. If the solution affects the usability, the user 
will not use it or may even try to disable or bypass the security solution. In the 
case of SMS encryption, the users are used to a nominal time required to send 
an SMS message, typically less than 10 seconds to receive a “Message sent” 
reply from the SMSC. If the encryption slows down the sending process 
significantly, the users will be frustrated and may choose to disable the 
encryption.
6. Overheads 
Encryption operations add overhead to the length of the original message. 
Many encryption algorithms encrypt data in fixed block sizes. If the data is larger 
than the block size the last part of the message is usually padded to the full block 
size and encrypted. The overhead for padding may not be significant for large 
messages. However, it may be quite significant for short message, such as those 
using SMS. For asymmetric encryption, the block sizes are relatively big because 
they are related to the key lengths. For example, the encryption of a single byte 
of data using RSA with 1024-bit key length yields a 256-byte output; a 2048-bit 
key length yields an output of 344 bytes. These overheads translate to additional 
transmission overheads, which in turn increases the power consumption. 
Therefore, the choice of an appropriate key length may reduce the overall power 
consumption without compromising the security.