As the challenge named as "Shifter salad", I think it would be a " vignere cipher" as it contains salad.
After using *vignere cipher*,I used AFFCTF as key.
It prints first 6 letters as ABCDEF.
May be this will be a hint. So, I used ABCDEFGHIJKLM. until I get the flag.
Then the flag is finally
Then, wrap it