Talk:Cryptography

Can someone provide an example of how to decrypt GTA IV AES Encryption through C++ (Key doesn't necessarily have to be included)?

Done. Do we really need to include implementation code for all the common hashes, though? --Steve-m 15:11, 15 February 2009 (UTC)

I think it's necessary for GTA's special CRC32 and One At A Time Hash (which I suppose isn't all that common). However I left SHA1 out because that is really common. Thanks for your decryption example, although do you have the library you used? --Sacky

No particular library, code is untested too. But there are tons of implementations that support those or similar functions, like OpenSSL, and usually every language/platform comes with its own library. Instead of decoding each block 16x you could as well decode all the data at once 16x (like aru does it), because of ECB that doesn't really matter (mathematically - although your CPU cache would be happier with the first method :p). --Steve-m 16:12, 16 February 2009 (UTC)

Please, can you post some code how to use AES Encryption in Delphi?

Sure. I used a stripped down version of AesLib.pas, I forgot where I got it from. Actual AES code is implemented in C and included via pre-compiled object files. --Steve-m 13:55, 17 February 2009 (UTC)

unit RockstarCrypt;

interface

const
  CKeyLength = 32;

type
  PAesKey = ^TAesKey;
  TAesKey = array[0..CKeyLength-1] of byte;

procedure RockstarDecrypt(Data: Pointer; Size: cardinal);

implementation

uses AesLib;

procedure RockstarDecrypt(Data: Pointer; Size: cardinal);
const
  CAesRounds = 16; // because it's 16x more secure!!1!
  CAesKey: array[0..CKeyLength-1] of byte = (
    $1A, $B5, ... // put the full key here or load it from the exe
  );
var
  AesCtx: TAesContext;
  i, j: Cardinal;
  p: Pointer;
begin
  aes_set_decrypt_key(@CAesKey[0], CKeyLength, AesCtx);

  for i := 0 to Size div 16 - 1 do begin
    Cardinal(p) := Cardinal(Data) + i*16;
    for j := 1 to CAesRounds do
      aes_decrypt_block(p^, p^, AesCtx);
  end;
end;

end.