Zodiackillersite.com

My understanding of a transposition cipher is that the plaintext remains as is but is rearranged to some standard.

My understanding of a substitution cipher is that the plaintext is substituted by some other letter, symbol, number, etc and remains unchanged after solve.

The two are combined for added security. Not sure that im really clear on how they are combined so i am looking for a dumbed down explanation.

When I think about the above transposition/substitution ciphering and, look at the 340, the definitions of both seem apparent. You have things like HER at the start that could be transposition and then you have the symbols that could be substitution. Is it possible to do a frequency on the symbols and solve for the symbols then work to find what order the transposition is?

Did Zodiac even do anything like that?

What if the apparent plaintext is substitution and the symbols are transposition? Is that possible?

I thank you in advance for your time.

Soze

Soze: Read pages 94-96 ( the actual paper book pages ) of Part IV of the NSA document on Military Cryptanalysis. That should answer a lot of your questions. We are saying that he probably transposed the plaintext message, then encoded the transposed message with 63 symbols. The book says to un-transpose the message first before trying to figure out what letters the 63 symbols represent. Which should be easy if the message is un-transposed correctly.

I took your advice and continued reading for the bulk of the day.

Thank you.

Soze