procedure InitDecryption;
  var
    Salt: TSetupSalt;
    MD5Context: TMD5Context;
    MD5Hash: TMD5Digest;
    SHA1Context: TSHA1Context;
    SHA1Hash: TSHA1Digest;
  begin
    { Read the salt }
    if FSourceF.Read(Salt, SizeOf(Salt)) <> SizeOf(Salt) then
      SourceIsCorrupted;

    if (Ver >= 5309) then
    begin
      { Initialize the key, which is the MD5 hash of the salt plus FCryptKey }
      SHA1Init(SHA1Context);
      SHA1Update(SHA1Context, Salt, SizeOf(Salt));
      SHA1Update(SHA1Context, Pointer(FCryptKey)^, Length(FCryptKey));
      SHA1Hash := SHA1Final(SHA1Context);
      ArcFourInit(FCryptContext, SHA1Hash, SizeOf(SHA1Hash));
    end else
    begin
      { Initialize the key, which is the MD5 hash of the salt plus FCryptKey }
      MD5Init(MD5Context);
      MD5Update(MD5Context, Salt, SizeOf(Salt));
      MD5Update(MD5Context, Pointer(FCryptKey)^, Length(FCryptKey));
      MD5Hash := MD5Final(MD5Context);
      ArcFourInit(FCryptContext, MD5Hash, SizeOf(MD5Hash));
    end;

function TFileExtractor.ReadProc(var Buf; Count: Longint): Longint;
var
  Buffer: Pointer;
  Left, Res: Cardinal;
begin
  Buffer := @Buf;
  Left := Count;
  if (FChunkBytesLeft.Hi = 0) and (FChunkBytesLeft.Lo < Left) then
    Left := FChunkBytesLeft.Lo;
  Result := Left;
  while Left <> 0 do begin
    Res := FSourceF.Read(Buffer^, Left);
    Dec64(FChunkBytesLeft, Res);

    { Decrypt the data after reading from the file }
    if FChunkEncrypted then
      ArcFourCrypt(FCryptContext, Buffer^, Buffer^, Res);

    if Left = Res then
      Break
    else begin
      Dec(Left, Res);
      Inc(Longint(Buffer), Res);
      { Go to next disk }
      if FOpenedSlice >= FChunkLastSlice then
        { Already on the last slice, so the file must be corrupted... }
        SourceIsCorrupted;
      OpenSlice(FOpenedSlice + 1);
    end;
  end;
end;