Question about the capabilities of a Turing machine.

Hi,

I go to school in Holland and I need to do a sort of term paper to graduate. Now I am doing a very simplified paper about Computer Sciences and cryptology. I do not know a lot about cs yet, but I am planning on studying it after I graduate. Now here is my question:

I am doing a small research on how to measure how secure a cryptology method is. I researched the subject and found the complexity theory, but that was far too advanced for me. So I decided to do research and simplify the awnser a bit. Now I am trying to turn several cryptology methods into simple additions, subtractions and multiplications. Then I interview a group of classmates and see how fast they can do simple additions, subtractions and multiplications. Using this I very roughly estimate how difficult it is for a human to crack a code and thus how safe it is. Now I have run into a problem. I started trying to apply this to the caesar shift and breaking the code using frequency analysis. At some stage in the code breaking one needs to look at the words and try to compare it to one in the known language. So for example you have the word np where you already have deciphered the letter n. The only word in the English language that fits in that word is no. Now I was trying to take this process and roughly state in a number of n subtractions, additions and multiplication, n being the number of letters in the cipher text. So my question is: is what I am trying to do possible and can a Turing Machine read words given that it is given a database of those words?

Sorry for any grammatical errors. I hope someone can awnser my question soon.