Peter Broman; Ola Liljerum , pp. 33. Inst. för Programvaruteknik och Datavetenskap/Dept. of Software Engineering and Computer Science, 2001.
Today the Internet is used more and more as a transportation for information. Much of the information is confidential and should not be read by those not privileged. To protect the information from unauthorized access cryptography can be applied. The cryptography algorithms in use today all have their pros and cons. They are therefore suited for different applications. We've compared three different cryptography algorithms RSA, DES and IDEA. What we've focused on is the level of security the algorithms give.
DES and IDEA are symmetrical algorithms and as such they use the same key for encryption and decryption. RSA on the other hand is an asymmetrical algorithm. Asymmetrical algorithms use two keys, one for encryption and the other for decryption.
The factor that is most decisive for the algorithms security is the length of the key that is used. What is interesting concerning the keys is that security increases linearly for the symmetrical algorithms, as the key length increases. For asymmetrical algorithms it increases on an expontiell curve.
RSA has got a big advantage compared to DES and IDEA. The advantage is key management. RSA can be used to exchange symmetrical keys in a safe way. The big disadvantage of RSA is that it's very slow to use. According to measurements that we have seen it is about 3 to 4 times slower then DES and IDEA during encryption, when using a key length of 1024 bits. At decryption RSA is about 120 times slower using a key length of 1024 bits. DES on the other hand is slower then newer symmetrical algorithms such as IDEA. This makes it uncalled for to use it in it?s original shape as it?s obsolete and insecure. Using DES will only give a false sense of security, unless the information doesn't need to be secure for more then a short time period.
IDEA offers high using it's 128 bits key and it's also the fastest of the two symmetrical algorithms, compared to the level of security that it offers. IDEA today has no known weaknesses and it has not been broken. Of the three IDEA is the best choice to use when it concerns cryptography of information, for example information which is stored on a hard disc, or information that is sent in e-commerce.