"Verschlüsselte" Bilddateien "entschlüsseln"

[jfheins]

Hallo, versuche doch mal diesen Code, um die MD5-Hashs zu ersetzen:

Delphi-Quellcode:

type
  MD5Digest: Array [0..15] of byte

type 
  MD5Digest: Array [0..15] of byte 

procedure Replace(Stream: TStream; oldmd5, newmd5: MD5Digest) 
var 
  i: Integer; 
  pos: Int64; 
  pattern: MD5Digest; 
begin 
  for i = 0 to 15 do 
  begin 
    oldmd5[i] := oldmd5[i] xor $8D; 
    newmd5[i] := newmd5[i] xor $8D; 
  end; 
  
  Stream.Position := 0;

  while (Stream.size - Stream.Position) >= sizeof(MD5Digest) do 
  begin 
    pos := Stream.Position; 
  
    Stream.readbuffer(pattern, sizeof(MD5Digest)); 
    
    Stream.position = pos + 1; // Wir müssen byteweise vorgehen 
    
    if (comparemem(@pattern[0], @oldmd5[0], sizeof(MD5Digest)) = 0) then 
    begin 
      Stream.position = pos; 
      Stream.writeBuffer(newmd5, sizeof(MD5Digest)); 
      break; 
    end; 
  end; 
end; 

procedure ReplaceFile(FileName: String; old, new: Array of MD5Digest) 
var 
  fs: TFileStream; 
  mem: TmemoryStream; 
  i: Integer; 
begin 

  mem := TMemoryStream.Create(); 

  fs := TFileStream.Create(FileName, fmOpenReadWrite or fmShareExclusive); 
  try 
    mem.CopyFrom(fs, 0); 
    
    for i = low(old) to high(old) do 
    begin 
      Replace(mem, old[i], new[i]); 
    end; 
    
    fs.CopyFrom(mem, 0); 
    
  finally 
    fs.Free; 
    mem.Free; 
  end; 
end;

So ähnlich zumndest