> restart:
# Umwandlungen
> bits2number := proc( X )
>   local x,i;
>   x:=0:
>   for i to nops(X) do
>     x:=2*x+X[nops(X)+1-i];
>   od;
>   x;
> end:
> number2bits := proc( xx, l )
>   local X,x;
>   x:=xx;
>   X:=NULL;
>   to l do
>     x:=iquo( x, 2, 'r' );
>     X:=(X,r);
>   od;
>   if x<>0 then print("Warnung: Informationsverlust! ",x); fi;
>   [eval(X)];
> end:
> bytes2number := proc( X )
>   local x,i;
>   x:=0:
>   for i to nops(X) do
>     x:=256*x+X[nops(X)+1-i];
>   od;
>   x;
> end:
> number2bytes := proc( xx, l )
>   local X,x;
>   x:=xx;
>   X:=NULL;
>   to l do
>     x:=iquo( x, 256, 'r' );
>     X:=(X,r);
>   od;
>   if x<>0 then print("Warnung: Informationsverlust! ",x); fi;
>   [eval(X)];
> end:
> words2number := proc( X )
>   local x,i;
>   x:=0:
>   for i to nops(X) do
>     x:=256^2*x+X[nops(X)+1-i];
>   od;
>   x;
> end:
> number2words := proc( xx, l )
>   local X,x;
>   x:=xx;
>   X:=NULL;
>   to l do
>     x:=iquo( x, 256^2, 'r' );
>     X:=(X,r);
>   od;
>   if x<>0 then print("Warnung: Informationsverlust! ",x); fi;
>   [eval(X)];
> end:
# Prozeduren
> erzeuge_Rundenschluessel:=proc(k)
>   global R,K;
>   local p,i,j;
>   K:=k;
>   R:=array(1..9,1..6):
>   p:=0:
>   for i to 9 do
>     for j to 6 do
>       R[i,j]:=K mod 2^16;
>       K:=K * 2^112 mod (2^128-1);
>       p:=p+1;
>       if p=128/16 then
>         p:=0:
>         K:=K*2^25 mod (2^128-1):
>       fi;
>     od;
>   od;
>   eval(R);
> end:
> mult16:=proc(x,y)
>   local X,Y,Z;
>   X:=x; Y:=y;
>   if X=0 then X:=2^16; fi;
>   if Y=0 then Y:=2^16; fi;
>   Z:=(X*Y) mod (2^16+1);
>   if Z=2^16 then Z:=0; fi;
>   Z;
> end:
> inv16:=proc(x)
>   local X,Z;
>   X:=x;
>   if X=0 then X:=2^16; fi;
>   Z:=X&^(-1) mod (2^16+1);
>   if Z=2^16 then Z:=0; fi;
>   Z;
> end:
> xor16:=proc(x,y)
>   local i,X,Y,Z;
>   X:=number2bits(x,16);
>   Y:=number2bits(y,16);
>   Z:=NULL;
>   for i to 16 do
>     Z:=eval(Z),(X[i]+Y[i])mod 2;
>   od;
>   bits2number([eval(Z)]);
> end:
> sum16:=proc(x,y)
>   (x+y) mod 2^16;
> end:
> encrypt:=proc(x)
>   global R;
>   local i,y,Y,Z,a,b,c;
>   Y:=number2words(x,4);
>   Z:=[0,0,0,0];
>   for i to 9 do
>     Z[1]:= mult16( Y[1] , R[i,1] );
>     Z[2]:= sum16( Y[2] , R[i,2] );
>     Z[3]:= sum16( Y[3] , R[i,3] );
>     Z[4]:= mult16( Y[4] , R[i,4] );
>     if (i=9) then break; fi;
>     a:= mult16( xor16( Z[1], Z[3] ), R[i,5] );
>     b:= mult16( sum16( xor16( Z[2], Z[4] ), a ), R[i,6] );
>     c:= sum16( a, b );
>     Y[1]:= xor16( Z[1], b );
>     Y[2]:= xor16( Z[3], b );
>     Y[3]:= xor16( Z[2], c );
>     Y[4]:= xor16( Z[4], c );
>   od;
>   words2number(Z);
> end:
> encryptfile:=proc(infile,outfile)
>   local st,INPUT,OUTPUT,x,y,X,Y;
>   st:=time():
>   INPUT:=fopen(infile,READ,BINARY);
>   OUTPUT:=fopen(outfile,WRITE,BINARY);
>   do
>     X:=readbytes( INPUT, 8 );
>     if X=0 then break; fi;
>     x:=bytes2number( X );
>     y:=encrypt( x );
>     Y:=number2bytes( y, 8 );
>     writebytes( OUTPUT, Y );
>   od:
>   fclose(INPUT),fclose(OUTPUT);
>   time()-st;
> end:
> 
# Test
> isprime(2^16+1);
> erzeuge_Rundenschluessel(1);
> rand(2^64)();
> decrypt(%);
> encrypt(%);
> KEY:="7654321GEHEIMNIS";
> K:=bytes2number(convert(KEY,bytes)):
> iquo(%,2^56) - bytes2number(convert("GEHEIMNIS",bytes));
> erzeuge_Rundenschluessel(K);
> FOLDER:="MYFOLDER/":
> decryptfile("".FOLDER."ideaklar.txt","".FOLDER."ideaklar.crypt");
> encryptfile("".FOLDER."ideaklar.crypt","".FOLDER."ideaklar.decrypt");
>