Reply To: Yet another 10B post
A three needle telegraph can only hold six characters (as per the clue) and the only six character cipher I can fin is the ADFGVX cipher. But surely this can’t be as this cipher was discovered after Ada and Charles’ time. And assuming the three needle telegraph follows the same logic as a six needle or five needle one which letter is /// pointing to? My confusion cannot be put into words. I really must complement the difficulty of this years challenge seeing as it only took me till quarter past eleven (painstakingly close to the second deadline) on the Thursday of release last time.
Thanks for the compliment! As you now know, the 10B cipher this year was inspired by the ADFGVX cipher, but it wasn’t exactly that and could have been discovered by our protagonists. The ideas of substitution and transposition were know to them, as was the Polybius square. Indexing the rows and columns by the 3 needle telegraph code would have been a natural idea. We have never insisted on strict historical accuracy with our choice of final challenge ciphers, not least because you lot would find that far too easy! In any case, while it was inspired by the ADFGVX cipher, it was different. We often design our own ciphers to keep things interesting and make you think and that is what we did this time.
By choosing to index the rows and columns with a three needle code instead of using two needles we introduced a weakness while disguising the frequencies. The third needle ensured that every character in the cipher text appeared with exactly the same frequency. that slowed a lot of you down for a long time. But it also introduced a check sum which meant that you could use the local distribution of characters to determine the transposition used in the first stage of the encryption. You will be able to read how the winners used that when we publish their accounts for the prize giving.