Cryptography puzzle
Hey guys!
I have this cryptography puzzle that I am struggling with.
The puzzle is as follows:
"There is a secret message intercepted which goes like this:
SDZROZDBITGNUMYNSF
Unfortunately the receiver could not interpret the message so the message was sent again but now looked like this:
YHDRCRLBUTIPUCMFGF
What was the message? What was the key used?"
I checked and these are not Caesar ciphers nor Affine ciphers. As there are so few letters I was unable to try frequency analysis. One thing I noticed is that the letters from both messages have uneven number of letters between each other e.g. the first letter of the first message is S and it's the 19th letter (counting A as 1) and the first letter from the second message is Y and it's 25th (inbetween are 5 letters) and so on.
Also, there are 5 pairs of letters that are the same and in the same position. R(4th), B (8th), T (10th), U(13th) and F(18th).
My logic also follows that if this is the same message then there must be something that is differentiating it every time. The most rational conclusion is that a part of the message is a part of the key? Let's say the first letter states some sort of a key variable or something and the message follows after that.
Haven't gotten far so if you guys have any hints or sources I can use that would be helpful.
