See: - Part 1/3 - Part 3/3

Just a small update to my previous post about the Vigenere cipher

Following the same approach as in the cipher, I modified a few lines in the script to create the "decoder"... I won't paste the code here, because the script is 95% the same, but I have stored it in GITHUB.

Basically, some variables change:

• coder: input_text="en un lugar de la mancha de cuyo nombre no quiero acordarme"

• decoder: input_text="AU CG PQNIK HA SI FEJJPT HA JCRS JVUUVA UW JYELZH EYVZWENTM"

• coder: ciphertext = []

• decoder: cleartext = []

• coder: print("-> Output text: {0}".format(''.join(ciphertext)))

• decoder: print("-> Output text: {0}".format(''.join(cleartext)))

And the logic for the look up changes as well:

In the coder, we replace the letter in the input_text by the one in the matrix[n] :

for x,y in encryption_tuple:
    if source.find(x) == -1: 
        ciphertext.append(x)
    else:
        ref_row = matrix[0].index(y)
        ciphertext.append(matrix[ref_row][source.index(x)])

In the decoder, we look for the position (lets call it "y") of the letter in matrix[n] and replace it by the letter in the position "y" in the alphabet:

for x,y in encryption_tuple:
    if source.find(x) == -1: 
        cleartext.append(x)
    else:
        ref_row = matrix[0].index(y)
        cleartext.append(source[matrix[ref_row].index(x)])

The result is the expected:

-> Key: WHITE
-> Input text: AU CG PQNIK HA SI FEJJPT HA JCRS JVUUVA UW JYELZH EYVZWENTM
-> Output text: EN UN LUGAR DE LA MANCHA DE CUYO NOMBRE NO QUIERO ACORDARME

In the next (and last post) about Vigenere, I'll write another simple coder/decoder script but based in the mathematical concept

Laters!