One example of a Polyalphabetic Substitution cipher is the famous Vigenere cipher, which was thought to be unbreakable for almost 300 years! The Vigenere cipher uses the power of 26 possible shift ciphers.
How This Cipher Works:
1) Pick a keyword (for our example, the keyword will be "Josh").
2) Write your keyword across the top of the text you want to encipher, repeating it as many times as necessary.
3) For each letter, look at the letter of the keyword above it (if it was 'J', then you would go to the row that starts with a 'J'), and find that row in the Vigenere table pictured here.
4) Then find the column of your plaintext letter (for example, 'I', so the 9th column).
5) Finally, trace down that column until you reach the row you found before and write down the letter in the cell where they intersect (in this case, you find an 'R' there).
Example:
Keyword: j o s h j o s h j o s h j o s h j
Plaintext: i w a n t t o h a v e d i n n e r
Ciphertext: RKSUCHGOJJWKRBFLA Thus, the message "I want to have dinner!" comes out:
R K S U C H G O J J W K R B F L A
The Challenge:
Now it's your turn to try it! Provided below is an encrypted secret message that you need to decipher. I'm sure you're thinking "But how will I be able to decipher the message if I don't know the key word?" Just look to The Gospel According to St. John, Chapter 8 verses 31, 32:
31 Then said Jesus to those Jews which believed on him, If ye continue in my word, then are ye my disciples indeed;
32 And ye shall know the Truth, and the Truth shall make you free.
Short Version:
MYY ZYXRN FFLKYKPXJ IY NHU OGRGFQG AH DUG HKV HHA KVUESR DSLAXICXZ, ULN ISTZH TUW JCFWEV NKBMYM MOTK QX HKV HHA RVN KLTUS MV VFGIYXYYGK.
Longer Version (short version plus added message):
MYY ZYXRN FFLKYKPXJ IY NHU OGRGFQG AH DUG HKV HHA KVUESR DSLAXICXZ ULN ISTZH TUW JCFWEV NKBMYM MOTK QX HKV HHA RVN KLTUS MV VFGIYXYYGKMYY MYNKB HM ZFX BZ EVUKUXU FBUX LJHU EZHX HGU JKLVVJM BIFH IYXTYIA YFL MOTK CL OHN CM TNJN UL MYY FFLKYKPXJ UKL LZGISR DSLAXICXZ UVWTBLV QX OTMY GVM PYM SXRLGLW FL FHLKYKLW KBX WKVWXKBEA IYBEWBWEVM GLVVMLHKP NH JHDJKLAVHW AAV HXEM
Good Luck!
