# Cipher: First time

So, this is my first puzzle here and it is a cipher. But it starts with an instructional poem:

The cipher below
Shouldn't forebode
It is but a version
Of a known code

Start at a place
And move forward a nip
Then forward again
Old letters do skip

The previous stanza
Describes the encoding
What you must do
Is find the decoding

UEIHTSODPTOALTTZKPPERARSRETICTYLERKEMHIIIORSIAILZTSANHS OSOWEQHTSPYUEDSRDFORSHJITOIDORITTACEEEHAMSAAKDAENJUQ

Hint 1

Decoding the cipher requires two parameters. The title holds a big clue to their values.

Hint 2

Neo1009 has identified the type of cipher. Such a cipher doesn't need to start at the first letter of the original message.

Hint 3

The title of this cipher ("First time") gives only two possibilities for the cipher's parameters, i.e. the starting position and the interval. The last clue needed is how this cipher differs from its standard version. That clue is given by the last line of the second stanza.

we are dealing with a "Skip"-Cipher (no official name found), it is technically a transposition cipher

The hints in the second stanza were

Start at a place So we have a cipher with an offset
move forward a nip then forward again We have an interval of moves/skips
Old letters do skip a slight modification to skip over letters you already encoded.

So the encoding is

1. Start at an offset $$O$$ in the plaintext
2. Output that letter to ciphertext
3. Delete that letter in plaintext (skip) 4. Move on in the plaintext, skipping $$I$$ letters
5. When reaching the end of plaintext, continue counting at the beginning ("modulo")
6. If there are still letters in plaintext, Go to Step 2

What we had to do according to stanza 3 is to find out

the decoding algorithm, because it is not symmetrical (i.e. encoding and decoding is not the same)
The only algorithm I come up with was
1. Encode an array of numbers 1..(length of message) with the encoding parameters $$I$$ and $$O$$
2. Sort the ciphertext letters according to the numbers in the encoded array

Lets do that

With the encoding parameters O=4 and I=4 and an array with 107 elements sorted from 1 to 107
we get the decoding-array $$4,9,14,19,24,29,34,39,44,49,54,59,64,69,74,79,84,89,94,99,104,2,8,15,21,27,33,40,46,52,58,65,71,77,83,90,96,102,1,10,17,25,32,41,48,56,63,72,80,87,95,103,5,13,23,35,43,53,62,73,82,92,101,6,18,30,42,55,67,78,91,105,11,26,38,57,70,86,100,12,31,50,68,88,107,22,47,75,97,16,45,76,106,36,66,3,51,93,37,98,61,28,20,60,85,7,81$$
This tells us
take the first ciphertext-letter and put it on position 4, the second ciphertext-letter to position 9 and so on

The decoded message:

with proper spaces:
I AM UNSURE IF THIS CIPHER IS TOO EASY OR TOO HARD I SUSPECT IT IS TOO EASY AND WILL ADD THE LETTERS ZZQQKKJJ TO PERHAPS MAKE IT HARDER

with proper casing and punctuation:
I am unsure if this cipher is too easy or too hard. I suspect it is too easy and will add the letters "ZZQQKKJJ" to perhaps make it harder.

• Congratulations! – Jens Oct 7 at 19:18
• FYI, the intention of the clue from the cipher title "First time" ($5$ letters and $4$ letters) was to indicate the parameters of the cipher, i.e. the encoding moves $5$ letters forward every time, starting at the $4$th letter. – Jens Oct 7 at 20:59

I believe this cipher is

A "Fixed Distance Cipher" decryption is not reciprocal to encryption. A type of transposition where you write the message and take off the letters according to some plan.

Hello my friends 2 (LETTERS BETWEEN ENCRYPTION LETTERS)
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v
HLYIDEOFESLMRN

• You are on the right track. :) – Jens Oct 3 at 14:38