# Text to integer

In public-key cryptography, one often needs to calculate the exponentiation. For example, you have a message

and some integer like Part of the encryption process is to calculateBut wait! How can you calculate something like that if

is a string.Bob immediately had a few ideas when he came across this problem. Bob is never short of ideas. He knows how to solve problems. You know, you first translate a problem into a simpler one.

The message

seemed too long. Bob simply used instead.Bob wrote:

How can you convert this into a number? Well, here's what Bob did:

Looks nice, right?

But, to calculate the value of the tower Bob still had to assign some numbers to the letters

Bob did the following:

If other letters are needed Bob will simply define mappings for those letters too.

Thus:

Wow.

seems huge. Perhaps Bob's tower isn't so efficient after all. No worries, though.Bob found a solution in seconds:

There is one small problem though:

But that's not such a big deal, right? Everybody knows nobody wants to encrypt

Everybody wants to encryptHowever, it turns out that cryptographers already have some clever solutions for converting text into an integer.

### Somewhat boring way to convert text to an integer

First of all, there are many character encodings that map characters to numbers. For example, UTF-8 maps character

to to to to and toOr, it maps

to:Using hexadecimal system, this would be:

In the hexadecimal system, each number occupies two places, so we can write:

The text

is finally converted to the number as follows:If for some strange reason, somebody wants to calculate

where is a totally meaningful message it can be done just like that:But that tends to be kind of a large number, right? No worries! This is where modular arithmetic comes into play.