Wireless Security.pdf - PDF Archive

Standardizing Security 243
AES can be implemented completely in software or completely in hardware. More
recently, a hybrid approach has been taken, moving some of the more expensive
operations into hardware while leaving the rest of the implementation in software.
This new approach has several distinct advantages. The hardware, not being dedicated
specifically to AES, can be more general and less expensive. Having the hardware
acceleration, however, makes the software smaller and faster. Several companies provide
various levels of AES acceleration, even going so far as to add specific AES instructions
into a processor so that no external hardware devices are needed. Generally speaking, if
you need a symmetric encryption algorithm for an application, you should use AES. It is
the safest choice because it is the standard used by the US government and it is backed by
some of the leading experts in cryptography. If AES is ever broken, it won’t be your fault
(and it wouldn’t matter anyway, since everyone else would be in big trouble too).
10.3.2.4 RSA
The three algorithms we have looked at so far are all symmetric-key algorithms that are
very useful if you have a good way to exchange keys with the person or machine with
which you want to communicate. In some cases, a physical transfer of the key may be
possible and appropriate, but more often, an electronic means of key delivery is more
applicable. Today, in most cases, this method is RSA. Developed and patented by Ronald
Rivest, Adi Shamir, and Leonard Adleman in 1978, RSA is the most well-known and
probably most useful public-key algorithm. One of the most useful properties of RSA
is that it can be used both for the basic public-key operation (I send you my public-key
so you can encrypt a message to send back to me), and for authentication (I encrypt
a message with my private key which you can verify came from me using my known
public-key). This property makes RSA especially useful for protocols that utilize both a
public-key operation and authentication, like SSL.
RSA is an elegantly simple algorithm with some extremely complex math behind it.
Essentially, RSA consists of a function that utilizes some unique properties of large prime
numbers and modular mathematics. The key generation for RSA involves selecting two
very large prime numbers and multiplying them together. The trick is that if you know the
prime factors used to generate the key then the RSA encryption function is simple to reverse
(thereby decrypting an encrypted message). If you don’t know those factors, then you have
to find them by factoring a REALLY large number into its component prime factors, a
process that takes an extremely long time using today’s math and technology. It is possible
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