A Vigenere cipher. It works by taking the key that you input, repeating it to the same length of the text, and then rotates the alphabet with which it encrypts. You can read more about it
here.
Thanks, BlindWanderer for the tip about using strings as opposed to lists.
string _key = "goat";
string keyRepeat(string text, string ky){
integer i;
integer j;
integer l = llStringLength(text);
string out;
for(i = 0; i <= l; ++i){
out += llGetSubString(ky,j,j);
if(j == llStringLength(ky)){
j = 0;
} else {
++j;
}
}
return out;
}
string encrypt(string text, string ky){
string alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz. ,!?&";
ky = keyRepeat(text,ky);
list t = llParseString2List(text,[],[]);
integer l = llGetListLength(t);
integer i;
string o;
integer prev;
for(i = 0; i < l; ++i){
integer x;
integer y = llStringLength(llList2String(t,i));
string ky_temp = llGetSubString(ky,prev,llStringLength(llList2String(t,i)));
prev = llStringLength(llList2String(t,i));
for(x = 0; x < y; ++x){
integer text_p = llSubStringIndex(alphabet,llGetSubString(llList2String(t,i),x,x));
integer key_p = llSubStringIndex(alphabet,llGetSubString(ky_temp,x,x));
integer pos = (text_p + key_p)%57;
o += llGetSubString(alphabet,pos,pos);
}
o += " ";
}
return o;
}
string decrypt(string text, string ky){
string alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz. ,!?&";
ky = keyRepeat(text,ky);
list t = llParseString2List(text,[],[]);
integer l = llGetListLength(t);
integer i;
string o;
integer prev;
for(i = 0; i < l; ++i){
integer x;
integer y = llStringLength(llList2String(t,i));
string ky_temp = llGetSubString(ky,prev,llStringLength(llList2String(t,i)));
prev = llStringLength(llList2String(t,i));
for(x = 0; x < y; ++x){
integer text_p = llSubStringIndex(alphabet,llGetSubString(llList2String(t,i),x,x));
integer key_p = llSubStringIndex(alphabet,llGetSubString(ky_temp,x,x));
integer pos = (text_p - key_p + 57)%57;
o += llGetSubString(alphabet,pos,pos);
}
o += " ";
}
return o;
}
default{
state_entry(){
llListen(0,"",llGetOwner(),"");
llSetObjectName("Cipher");
}
listen(integer c, string n, key i, string ms){
list m = llParseString2List(ms,[":"],[]);
if(llList2String(m,0) == "encrypt"){
llSay(0,encrypt(llList2String(m,1),_key));
} else if(llList2String(m,0) == "decrypt"){
llSay(0,decrypt(llList2String(m,1),_key));
} else if(llList2String(m,0) == "key"){
_key = llList2String(m,1);
llSay(0,"Key set to \""+_key+"\".");
}
}
}