encode:=function(message,blocksize)
local letters,digits,code,i,out,len;
letters:=[" ","a","b","c","d","e","f","g","h","i","j","k",
"l","m","n","o","p","q","r","s","t","u","v","w","x","y",
"z","A","B","C","D","E","F","G","H","I","J","K","L","M",
"N","O","P","Q","R","S","T","U","V","W","X","Y","Z",
",",".","?","!","'"];
code:=ShallowCopy(message);
for i in [1..Length(letters)] do
    code:=ReplacedString(code,letters[i],String(i+9));
od;
len:=Length(code);
out:=[];
for i in [1..(len-(len mod blocksize))/blocksize] do
    out[i]:=Int(code{[(i-1)*blocksize+1..i*blocksize]});
od;
if (len mod blocksize) > 0 then
   out[Length(out)+1]:=Int(code{[len-(len mod blocksize)+1..len]});
fi;
return out;
end;
decode:=function(code,blocksize)
local letters,message,i,out,temp;
letters:=[" ","a","b","c","d","e","f","g","h","i","j","k",
"l","m","n","o","p","q","r","s","t","u","v","w","x","y",
"z","A","B","C","D","E","F","G","H","I","J","K","L","M",
"N","O","P","Q","R","S","T","U","V","W","X","Y","Z",
",",".","?","!","'"];
message:=List(code,x->String(x));
for i in [1..Length(message)-1] do
    if Length(message[i])<blocksize then
       message[i]:=Concatenation("0",message[i]);
    fi;
od;
temp:=JoinStringsWithSeparator(message,"");
if (Length(temp) mod 2) = 1 then
   message[Length(message)]:=Concatenation("0",message[Length(message)]);
   temp:=JoinStringsWithSeparator(message,"");
fi;
out:=[];
for i in [1..Length(temp)/2] do
    out[i]:=letters[Int(temp{[2*i-1..2*i]})-9];
od;
out:=JoinStringsWithSeparator(out,"");
return out;
end;