#substitutioncipher

[shadowwolf387c]

The Caesar Cipher

Historically, most books explain that Caesar used a shift of 3. It is also likely that Caesar used only upper case letters in his messages though I've never seen any notes on actual messages. This is perhaps the weakest of the substitution ciphers because it only has 26 different keys.

The program is pretty straight forward and it retains both upper and lower case as well as punctuation. Unlike the core/Rot13 program, this one has a variable shift key and it allows encrypt and decrypt modes.

Below is a ciphertext example. You'll have to forgive my sense of humor.

Vjku ku c vguv qh vjg uwrgt ugetgv ekrjgt.

Vjku ku qpna c vguv. Kh vjku jcf dggp cp cevwcn

gxgpv, uqogqpg yqwnf dg ncwijkpi jauvgtkecnna

cv vjg rqqt ejqkeg qh gpetarvkqp.

There are a few modifications that are possible. Perhaps the most normal one would be conversion to upper case only. Following that would be to strip the punctuation and word divisions to create typical 5 letter groups. To be somewhat historic, the ciphertext should probably retain the word divisions at a minimum.

Note that if you use only upper case letters or only lower case letters, the program will retain that. If you omit punctuation or make 5 letter blocks then that will also be retained. Maybe the program doesn't do all the work, but it is plenty good enough to have some fun with.

Look for the letter frequency counter program to help crack this cipher. You could also try every letter of the alphabet and see which one worked.

Follow the github link to download files

#caesarcipher #cryptography #substitutioncipher #C #C++ #QB #sourcecode #executable

[comp6841lanceyoung]

Substitution Cipher Practice

Substitution Cipher #1

Reflections: focusing on the most frequent 3 letter words (ie. not ‘arm’) is useful. Just trying letters is more effective than sitting there doing nothing - the brain will naturally try and correct spelling and hence being willing to try combinations is better than nothing.

Substitution Cipher #2

Reflections: Focusing on the two letters first proved very helpful. For example, BR and HB - O would be a good guess for B. Trying other letters for R (N or F) and H (T or S) and seeing how they sit in other words was a useful strategy. Got this one pretty quick.

Substitution Cipher #3

Reflections: Guessing ING whenever you frequently see a 3 letter sequence at the end of multiple words was effective. In addition, single letters will most certainly be ‘I’ or ‘A’ - here, I could distinguish the two single letters via the sentence structure. At the beginning of the quote, having “A IS/IN/IT” is very unlikely and hence, G was mostly likely ‘I’.

Substitution Cipher #4

Reflections: Definitely the most difficult out of all the ciphers. Similarly to before, by just attempting letter substitutions, I was able to make deductions and working through the cipher faster than if I had just stared at the screen. 

Overall, I feel pretty confident that I’ll be able to handle any substitution ciphers under pressure in the exam. I just have to remember to stay calm and trust that I’ll be able to solve the cipher even if it doesn’t come to me immediately.

I think the first cipher’s quote from Marcus Aurelius is prevalent here.

#cryptographyPractice #SubstitutionCiphers #midsemprep

[comp6841lanceyoung]

Practicing Substitution Ciphers: Snapshot

I’ve been practicing cracking substitution ciphers - the following pastebin link stores some statistics on my current level of skill.

Hopefully, by practicing frequently throughout and having the habit to do weekly tests as above, I can watch my skills improve.

#practice substitutionCiphers prep4midterm