AES vs RC4

AES (Advanced Encryption Standard) and RC4 are two encryption ciphers that are used in a variety of applications. A common example where you would see both ciphers employed is in wireless routers. Although you would not explicitly see RC4 as an encryption mechanism there, both WEP and TKIP implement the RC4 cipher. Whereas AES is relatively new and very complex, RC4 is very old and is very simple.

The most significant difference between the two would probably be their type. AES is a block cipher that operates on discrete blocks of data using a fixed key and a formula while RC4 is a stream cipher that does not have a discrete block size. Instead, it uses a keystream of pseudorandom bits that is combined to the data using an exclusive OR (XOR) operation. You can use block ciphers as stream ciphers and vice versa, so the separation is not very distinct. But it is quite well known that RC4 is not very effective when used as a block cipher.

A good example of the weaknesses of RC4 is the implementation of WEP. WEP has been completely rendered insecure and can even be broken within a couple of minutes with tools that you can find readily available online. Although TKIP addresses some of the issues that have plagued WEP, it is not considered to be as secure as AES is. For this reason, it is advisable to use AES in any situation unless hardware limitations prevent you from doing so.

The primary reason why RC4 is very popular is the fact that it is simple and it can be very fast. This is already being mitigated since AES implementations in hardware are becoming very popular as it provides speed advantages over software implementations.

Lastly, RC4 is trademarked since it was initially a trade secret, which led to some people coming up of inventive ways to call the leaked description way back in 1994; like ARCFOUR and ARC4 (Alleged RC4). On the other hand, AES is publicly available and can be freely used without hitting any legal problem.

Summary:
1. AES is a very new and complex encryption standard while RC4 is rather old and simple
2. AES is a block cipher while RC4 is a stream cipher
3. AES is extremely secure while RC4 is not so
4. RC4 is very fast compared to AES
5. RC4 is trademarked while AES is not

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