Translating Python Code For Rc4 To Pascal

I'm attempting to translate RC4 from Python to Pascal. This is the working Python code (not written by me): def KSA(key): key_length = len(key) S = list(range(256)) j =

Solution 1:

Strings in Pascal are generally one-based (with the notable exception of the Delphi mobile compilers). I get the correct output if I change:

j := (j + S[i] + ord(key[i mod key_length])) mod 256;
...
cipher[i] := (keystream[i] xor ord(plaintext[i]));

to:

j := (j + S[i] + ord(key[i mod key_length + 1])) mod 256; // note: + 1
...
cipher[i] := (keystream[i] xorord(plaintext[i + 1]));    // note: + 1

If I do (e.g. in Delphi or FreePascal):

key := 'Secret';
plaintext := 'Attack at dawn';

...    

for I := 0 to Length(plaintext) - 1 do
  Write(Format('%.2x', [Cipher[I]]));
Writeln;

I get the cipher as:

45A01F645FC35B383552544B9BF5