The sixth hint for Challenge 10A
The Body in My Library › Forums › Harry’s Meeting Place › The official Challenge 10 tips and hints thread › The sixth hint for Challenge 10A
20th December 2023 at 9:00 am
#92784
Harry
Keymaster
The sixth hint for Challenge 10A
If Jodie sent this message and signed it we will see the bigrams OD, IE at the end and these are represented by the vectors (14, 3) and (8, 4).
What we actually see are the letter pairs RU, MQ which correspond to the vectors (17,20) and (12,16), so the encryption works to give
14a+3b = 17
14c+3d=20
8a+4b =12
8c+4d=16
We can solve these four equations in four unknowns to get the encryption parameters. Try looking up solving systems of equations online, but be careful doing so in mod 26 arithmetic!