This week we started learning a lot more content. Richard went over many new concepts and topics; some of the more primary ones being the vignere cipher, Enigma machines, One Time Pads and TI/TII errors. My notes from the 2 lectures can be found below.
A vignere cipher is a more advanced version of a Caesar cipher. In a caesar cipher, characters in a plain text are shifted by a certain number. This number denotes how many characters in the alphabet the value is shifted by. So, as an example, if the letter ‘A’ was shifted by a number of 6, the new value for this letter in the cipher text would be “”G”. In the event that the shift leads passed “Z”, the shift is cycled around back to “A”. So if we were to do the same shift from “Y” instead, the new cipher text value would be “”E”. Now a vignere cipher is essentially the same type of encryption however the shift pattern is denoted by a password. Let’s say the password is “ABBA”, this means to first shift the value by 1, then 2, 2, and 1. Once the end of the password is reached, the shift pattern cycles back to the beginning. This repeats until all the plain text is encrypted. This concept was very interesting to me, as I was already aware of the encrpytion method to shift the values in a plaintext by a certain number, but I had never come across the vignere cipher which extended upon this. It surprises me that one cipher can be evolved into a more concrete encryption method and reminds me how people in the world are always trying to improve and strengthen the encryption methods available to us.
Enigma machines are another extension upon the Caesar cipher. It too adds a password for the encryption, however this password is of almost infinite length. This is due to the use of a password extender. I did some research on how exactly these enigma machines work, within these machines are several rotors. Each of these rotors contained 26 letters from the alphabet on them. A rotor itself performs a simple substitution cipher, upon taking a letter from one side of the rotor, it displays another value on the opposite side. An enigma machine holds several of these rotors in line with each other, so that when a value is entered, each rotor sends a new substituted cipher value onto the next rotor, eventually leading final value in which the enigma machine uses. These machines are a fascintating encryption method to learn about and I highly recommend you read up on it.
One Time Pads (OTP) are yet another encryption method that was brought up in the lecture (I’m amazed at how many encryption methods actually exist). Like with enigma machines, I decided to look up more information on what an OTP is and how it works. The way it works is that a plain text is pared with a random secret key (this key is what the OTP is) whose length is equal to or longer than that of the plain text, the plain text is then encrypted using the secret key. How this encryption works is as follows. Each bit of the plaintext is combined with the corresponding bit from the key, through the use of modular addition. Now, in order for this method to remain somewhat hard to crack, the key must be kept hidden, must never be reused in the whole part (no duplicates of its presence), must be truly random (although according to Richard, this is very hard to achieve), and at least as long as the plain text. OTPs themselves seem like a very simple encryption method to me but this thought process might change when I begin to look up at how they are decrypted (because this course is primarily about how to break encryptions).
TI and TII errors are, as you can assume, are two types of errors that are associated with security measures. A TI error is when a result returns a false positive (i.e. it rejects a true null hypothesis). An example of this is if a medical test for a disease is run and states you do have the disease when in actuality you don’t. TI errors are when a result returns a false negative (i.e. fails to reject a null hypothesis). An example of this is if a medical test for a disease returns false when in actuality it is true. After attending both the lectures, tutorial and looking up these errors online, there is much debate over which is more important to remove. In my personal opinion, I believe that TII errors are more dangerous in terms of security, letting someone in who shouldn’t have access is more of a threat then not letting someone in who should have access. I also learnt from Richard and my tutor that you can’t remove the likelihood of one of these errors, without increasing the likelihood of the other.
