A nomenclator is a cipher with a codebook bolted on. Ordinary letters get enciphered one at a time. But important words — names, places, the word king — get their own single symbols, taken from a list that might run to hundreds of entries.
It is stronger than either half alone. The common words vanish entirely, so counting letters misses them, and the leftover letters are too few to attack. Mary, Queen of Scots used one, and its breaking cost her her head.
The cipher that cost a queen her head
Mary, Queen of Scots wrote to her supporters in a nomenclator, and believed it safe. Elizabeth’s spymaster had already broken it, and was reading every letter before Mary did. He waited until she wrote something that could be used against her, then added a forged postscript asking for the names of her fellow plotters. The reply convicted her.
Print this page and you get a worksheet: how the cipher works, where it came from, and the puzzles to crack, with the machine and the menus left off.
Print this page as a worksheet Its sheet in the pack Try the challengesLonger, harder and written for grown-ups. Worth a look when this page runs out.