The Final Tales of Sherlock Holmes - Volume 1 by John A. Little Page A

Hudson.
    The drumming ceased.
    â€˜Watson, we must act with more speed this time. Our friend seems to be always one step ahead of us. If I didn’t know you better, I might even begin to suspect you.’
    â€˜Holmes! How could you! What a thing to say!’
    â€˜I’m sorry, old man. It was just a little joke of mine, utterly facetious and inexcusable. Will you forgive me?’
    â€˜Oh, well. All right. But let’s work together from now on, not separately, as we have been doing. I believe that we have always worked better when our two minds are focused on a particular crime. I also believe that we should begin to include Lily in our undertakings.’
    â€˜Lily? But I thought you wanted to protect her from these vile crimes?’
    â€˜I don’t mean that she should play an active part, Holmes. I wouldn’t want to expose her to any danger. Certainly not. It’s just that she has a different viewpoint on life, and may know more about these types of crimes and their perpetrators than we realise.’
    â€˜I can’t accept that she would know anything about serial killers of so-called musical men, Watson. However, I agree. Provided she continues to bring me my tea and meals when I want them.’
    â€˜Good. Which reminds me. Have you had breakfast yet?’
    â€˜No. An excellent idea, Watson. And this also provides an opportunity to use Lily’s precious bell for the first time.’
    Holmes leaned back in his chair, picked up his stick sword and used it to press the bell.
    â€˜In the meantime, we must address our minds to the problem of the Vigenère cipher and find the name of the next victim. Sit over here beside me.’
    â€˜Oh, well. If I must, Holmes.’

Chapter XI. The Third Puzzle.
    â€˜The Vigenère cipher is a polyalphabetic cipher. It uses twenty-six different alphabetic sequences, each shifted successively by one letter to the right – called a Caesar shift after old Julius won some battle with it – and a keyword to move between them. This cipher was first broken by a chap named Charles Babbage using an invention called the Analytical Engine, an effective device that may have a decent future. The problem with breaking it lies in finding the keyword showing which lines in the alphabet sequence to use. This might make it clearer.’
    Holmes delved into a drawer in the table, rummaged around a bit, withdrew a document and handed it to me:

    â€˜Let us continue our example. I shall use a ruler and write this out on the pad as we go along. Each letter of the keyword shows the particular line within the square to be used, so if the keyword was WATSON and the message was HELLOOLDCHAP, it is encrypted by cycling through the six lines where the first letters are W,A,T,S,O,N. So H = D in line W, E = E in line A, L = E in line T, L = D in line S, O = C in line O, O = B in line N, L = H in line W, D = D in line A, C = V in line T, H = Z in line S, A = O in line O, P = C in line N. The cipher text becomes an apparently meaningless DEEDCBHDVZOC. To decrypt, the receiver reverses the process using the same keyword. Simple, isn’t it, Watson?’
    â€˜Eh? Oh, yes. It’s a complete doddle, Holmes. A piece of cake. Ah, at last.’
    Lily entered the room like my personal saviour, carrying a tray that issued forth an array of aromas, sufficient to make any mouth water.
    â€˜Though’ yer gen’lemen moight loike a spo’ o’ brekkie,’ she said placing the tray on the table.
    I needed no second bidding to tuck in, even though Holmes continued to babble on about codes and ciphers while we were eating.
    â€˜The sender and receiver could agree on a longer keyword, or the use of a key phrase to increase the complexity of the cipher. However, any polyalphabetic cipher has one inherent weakness, if a short key is used. It is the fact that the alphabets used for encryption are periodically repeated. That is what we must