This is not a puzzle, this is an actual question
I understand a Vigenere cipher has 3 parts: the plain text, the key and the encrypted text. It is my understanding you would need at least two of these parts; however, the guide seems to suggest you can use the index of coincidence to find the key from the encrypted text, although I may be wrong.
I seem to do okay with Wikipedia's example:
Here Wikipedia explains that the key would simply be repeated to make as many characters as the encrypted text / plain text, so it comes out as LEMONLEMONLE.
From there and using their helpful image (attached as it appears to be in public domain) (click for larger version)
I understand that looking at the
L row from the first column (the first letter in the key), and finding the
L (first letter of encrypted) in that row, I get
A. Using the same logic for the rest:
Row L pos L = A Row E pos X = T Row M pos F = T Row O pos O = A Row N pos P = C Row L pos V = K Row E pos E = A Row M pos F = T
and so forth; however, I tried to apply this logic to a puzzle, who's encypted text was cicessrt and key was cantwait, and all I got was gibberish:
Row c pos c = a Row i pos a = s Row c pos n = l Row e pos t = p Row s pos w = e Row s pos a = i Row r pos i = r Row t pos t = a
The answer is actually meant to be
It feels like I tried and double checked everything, including swapping the key + encrypted text (which gives more gibberish) and attempting to start with the plain text and use the key to get the encrypted text (more gibberish), and I'm at a loss. Given the encrypted text and the key, how is it possible to solve the Vigenere cipher? What did I do wrong?