Plaintext:
Congratulations if you can read this. This encryption's getting quite complicated. The Vigenere method of encryption commutes with a transposition if its row and column lengths are one more than a multiple of the keyword length, so in this case with a keyword of length wo, we need them to both be oddi. Hope you’ve enjoyed decrypting these messages. Why not try coming up with some ciphers yourself and testing your friends?
Method of encryption:
Firstly, Vigenere encryption by keyword "pi". Secondly, transposition of 15 columns.
Way to decipher:
By the hint from the previous cipher challenge, it should be encrypted with Vigenere encryption first then with transposition. So, to decipher, we have to work out the way of transposition first, then the keyword of the Vigenere encryption.
Since the number of characters in the message is 345, which has factors of 1,3,5,15,23,69,115,345, I tried to transpose the message in those numbers of columns, until I found repeating three-letter word in the message, which is likely to be 'the', the most common word in English. I found the number of columns to be 15.
After the transposition, I saw 4 repeating 'bwm'. Their seperations are 42, 32, 52 respectively, which have a gcd 2. There are also 4 repeating 'vvbw'. Their seperations are 104, 56, 42 respectively, also with gcd 2. Therefore, the keyword length should be 2. Comparing 'bwm' with 'the', the keyword should be 'pi' or 'ip'. By trying, the keyword is 'pi'.
In the plaintext, there are two words which are quite strange. They are 'wo' and 'oddi'.