My first obfuscation ever. I was bored.
for(@p=$n=2;$#p<20;$n++,$g=1){ for(@p){$g=0,last if!($n%$_); }push@p,$n if$g;}$c{$_}=$c++for 'A'..'Z';($d=join'',<DATA>)=~ s/\s+//g;print(('A'..'Z')[($c{ substr($d,$_,1)}+5)%26])for@p; __DATA__ XUEPXNO OJZYVKI ZDJ JPOA C A C S L X X D Z R M Y I KPEKDFG Z J MPNG G G P N G N C S V U X CVKXREK RHF N TIZSMUJGJIJWZIFNRHCNMMOQWIRNO