Ti-basic (the lauge that runs on ti-83 graphing calculators) if you know this   language convert to a normal luangege like JAVA  
:ClrHome  
:" abcdefghijklmnopqrstuvwxyz" //all symbols that can be interpreted  
:Ans+Ans+Ans->Str1  
:Menu("crippter","encript",1,"decript",2  
:Lbl 2  
:1->C  
:Lbl 1  
:if not(C)  
:Imput ">",Str2  
:if C  
:Imput "<",Str2  
:length(Str2)->D  
:lenght(Str1)/3->E  
:if not(C)  
:Then  
:randInt(1,E)->B  
:sub(Str1,B,1)->Str3  
:Else  
:inString(Str1,sub(Str2,1,1),1)->B  
":"->Str3  
:For(X,1+C,D  
:inString(Str1,sub(Str2,X,1)->A  
:if not(C  
:A+E-B-X->A  
:if C  
:A+B+X-1->A  
:Str3+sub(Str1,A,1)->Str3  
:End  
:if C  
:sub(Str3,2,D-1)->Str3  
:Pause Str3  
:Goto A  

Ps this is some nice encryption software (for a ti-83)  
Pps by ti-83 I mean any calculator in the ti-83 or ti-84 family  
Ppps "->" means "STORE" accessed by "STO>"