From figure 3 in the paper linked elsewhere in the thread <https://news.ycombinator.com/item?id=34718588 https://news.ycombinator.com/item?id=34718588>, it look

From figure 3 in the paper linked elsewhere in the thread <https://news.ycombinator.com/item?id=34718588 https://news.ycombinator.com/item?id=34718588>, it looks like 219 distinct symbols, most with diacritics, like a plus with a dot below it, or a 4 with a dot to the right. Edit: much further down it is also mentioned "Eventually, we were able to recover the meaning of almost all the 219 distinct symbol types". Wasn't sure if I had counted correctly! It's basically a substitution cipher, with some elements mapping to the same symbol to defeat frequency analysis and a few special ones like symbols for individual place, month, or person names, or a symbol to delete or duplicate the previous character. Edit2: figure 13 gives a good overview. There's no combinatorics involved like with modern ciphers.