Short Message Service (sms) security solution for mobile devices

Symmetric Key 
Length 
Asymmetric Key 
Length 
56 bits 
384 bits 
64 bits 
512 bits 
80 bits 
768 bits 
112 bits 
1792 bits 
128 bits 
2304 bits 
Table 2. Symmetric and Asymmetric Key Length Comparison 
Table 2 provides a reference for relative comparison of key lengths. 
However, this is still based on the current mathematical knowledge regarding 
factoring large numbers. Once a newer and faster method of factoring is 
discovered, the values in the table no longer hold. 
3. Key 
Management 
Key management is an important part of any encryption solution. The 
strongest algorithms and the longest keys are useless if the keys are not 
generated, distributed and destroyed in a secure manner. Stealing keys is an 
attractive option for the attacker because the attacker does not need to expend 
resources to break the encryption algorithm, if he can break the key generation 
algorithm. The attack of the COMP128 algorithm is an example of an attack on 
the key generation algorithm.
A big challenge in key generation is ensuring that the keys generated are 
truly random and thus not predictable. The difficulty depends on the key lengths 
and the frequency of key change. For One Time Pad, the keys are as long as the 
messages and the keys must never be repeated. This may be extremely difficult 
depending on the volume of traffic.
There are also known weak keys in certain algorithms. Therefore, after the 
key generation process, it is important that the keys be checked to ensure that 
they do not belong to the pool of known weak keys.

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After the keys have been generated, they must be distributed via a trusted 
communications channel. Key distribution for a large network can be 
cumbersome. For symmetric encryption, the number of key exchanges required 
in a network with 
n 
users is 
n(n – 1)/2
. The key exchange for asymmetric 
encryption is simpler because the public key can be exchanged via a public 
network. However, mechanisms must be built into the system to ensure the 
authenticity of the public keys.