Introduction to Cryptography with Coding Theory, 3rd Edition

B.7 Examples for Chapter 9

Example 22

Suppose you need to find a large random prime of 50 digits. Here is one way. The function nextprime finds the next prime greater than $x\text{.}$ The function rand(a..b)() gives a random integer between $a$ and $b\text{.}$ Combining these, we can find a prime:

> nextprime(rand($10^49$..$10^50$)())

         73050570031667109175215303340488313456708913284291

If we repeat this procedure, we should get another prime:

> nextprime(rand($10^49$..$10^50$)())

         97476407694931303255724326040586144145341054568331

Example 23

Suppose you want to change the text hellohowareyou to numbers:

> text2num("hellohowareyou")

                    805121215081523011805251521

Note that we are now using a = 1, b = 2, ..., z = 26, since otherwise a’s at the beginnings of messages ...