# What is the period of a cipher?

For the following explanation of RC4:

It is a variable key-size stream cipher with byte-oriented operations. The algorithm is based on the use of a random permutation. Analysis shows that the period of the cipher is overwhelmingly likely to be greater than $10^{100}$."

What does it mean by the period of the cipher and greater than $10^{100}$?

## 1 Answer

I think the 10100 is a typo and should be $10^{100}$ as shown here

The period would be something along the lines of how long until the byte stream repeats. For example if the byte stream were "ABCDABCDABCD" and so on, then the period would be 4.

For security you want a large period so that you can encrypt large amounts of data.