On Thu, 3 Jun 1993, A1 ray arachelian wrote:

...

2) does anybody know how the hell Stacker or DoubleStor or whatever executes the actual interception of the read/write routines and stacks them? I don't get it at all. I am more than willing to learn to get this thing working though.

Anyhow to make the story short, if I wrote an image mounter device driver which would be able to grab DIM files and pretend that they were on the A: or B: drive then we could also install the programs without breaking out the recylced disk box. :-)

Couldn't you just do that with the assign command in DOS? or is that a new command?

I never got around to it because of other projects, but, what you need to do is to write a device driver that becomes accessible via the IOCTL calls. That's the way logical drivers (such as Stacker) install themselves.

Yeah, I am assuming that is the way I will have to organize the system. I want it to be totally transparant, that seems like a good way.

Also, the program you're writing (I believe) has been already written and is part of Norton Utilities, but uses either DES or some other weak form of encryption. You might want to buy Norton Utilities and play with that program and see what makes it tick. Basically a program like MSD (Microsoft Diags) can tell you exactly what interrupts it patches itself into.

I have heard this from someone else. It kind of takes the wind out of my enthusiasm, but not too much... I still think that there is a need for a good, strong system out there with some seriously dedicated password key protection and such. Also, it needs to be freeware (or shareware, depending on how long it takes to write) so that security won't just be in the hands of the people who can afford to buy it from companies. I also think that it would be a lot more valuable if it were distributed with code so that any user who wanted could inspect it for trapdoors.

On to the sector remapping. The way stacker and doubledisk and the other suite of driver level compressors work is basically, they allocate a huge file on the hard drive, and then do a remapping at the sector level. That is you've got the data itself and an index table into the data for every sector. When a sector is written to the drive, the driver compresses the sector, so say, it was 512 bytes, it now becomes 128 bytes (if we're lucky) so what Stacker does is, looks in its index table, finds 128 bytes free in the huge file it allocated, writes the data there, and then sticks the position of the data, and it's size (after compression) in the index table. (Of course it also marks that 128 bytes as taken.)

Umm, perhaps this is overly optimistic, but I was hoping that I would be able to use an algorithm that did 1 byte in / 1 byte out encryption so that I wouldn't have to deal with sector remapping. This would greatly speed up the process, make it more crashproof, and besides, it would be a hell of a lot easier... I was thinking that I would even basically leave the FAT and such intact, or at least only slightly modified.

I believe it also does some other funky stuff like changes the allocation table or the bytes free to twice the space it's got left, so that DOS doesn't choke when it thought it had 10,000 sectors free and the hard drive ran out of space when it tried to write #4,999. :-)

So you might want to do this with RSA. But better yet, why don't you find a quick compressor algorithm (say some sort of LZ type method) and stick that in as well. This way you are writing a public domain version of stacker >WITH< encryption. (Since you'd have to remap the sectors anyhow, you might as well compress them too...)

I have been pointed in the direction of the IDEA engine in PGP, which will take 1 byte in / 1 byte out. This would be ideal (snicker) for the reasons that I mentioned before. As for compressing also, that is a really good idea, but I think that I will leave that one up to posterity, or at least to the next guy that tries to midofy the thing, I am concerned enough with getting it to work at all, and compression would add the problem of having to do sector remapping, which I would like to avoid at first.

The above is just a theory and hasn't been tested. I believe that this is what Stacker does, but I'm not exactly sure. :-) But it does sound logically right.

Sounds good to me, and it is consistent with the advice of others (thanks a lot guys, I really appreciate the help) and the books that I have found since this started two days ago...

So if I'm wrong, let me know as you've got my curiosity up in this matter.

I'll keep everyone updated no problem. How else am I going to get suggestions and help? -Ryan the Bit Wallah