# What does this "ordinal cipher" say?

I invented (I think) a kind of cipher! What does this message say?:

first fifthhsecondngfourth firstsecondthirdfourthfifth, fourthecoseventhd fifthsixthsecondseventheighthfourth fourthninthtentheleventhseventhtwelfth

Hint:

this one thirdfourth mucsecond seventhafourththirdseventhr

## Decryption method

A couple of the "words" are easy to recognise as actual words:

first ThIngS firstsecondthirdfourthfifth, SecoNd fifthsixthsecondseventheighthfourth fourthninthtentheleventhseventhtwelfth

That means

second = I, fourth = S, fifth = T, seventh = N

so I suspect that

these ordinals may be letters in some "key" word (?I?ST?N...) and the message itself becomes

first ThIngS firstIthirdST, SecoNd TsixthINeighthS SninthtentheleventhNtwelfth

## Solution

It's now clear that the message is

FIRST THINGS FIRST, SECOND THINGS SECOND

so the ordinals are

first = F, second = I, third = R, fourth = S, fifth = T, sixth = H, seventh = N, eighth = G, ninth = E, tenth = C, eleventh = O, twelfth = D

and the system is

to generate ordinals from the letters of the plaintext itself and then apply them to encrypt it to the ciphertext.

This is also consistent with the hint.

• Ah... I was on the right track but didn't realize that not all substitutions were uniformly applied. Nice solve!
– Avi
Sep 3, 2021 at 19:38