5 ms·

IMO Dungeon Master for the Atari ST & Amiga has the greatest copy protection scheme ever created. It utilized (amongst a multitude of other things) something ca

by Nr7 10y ago

IMO Dungeon Master for the Atari ST & Amiga has the greatest copy protection scheme ever created. It utilized (amongst a multitude of other things) something called "fuzzy bits" that were bits which values were not set but could be either "0" or "1" when read. >If you copy your original Dungeon Master floppy disk using your favorite disk copier, the copy will not have the fuzzy bits but normal bits instead. The game can easily detect their presence by reading these bits several times: if it gets random results, then it assumes the disk is original. If it gets consistent results, it assumes the disk is a copy. http://dmweb.free.fr/?q=node/210 http://dmweb.free.fr/?q=node/210

jonathankoren 10y ago
This worked because the magnetic domains on the disk were larger than the r/w head on drive, and due to play in the servo mechanism. It's the same reason why the DOD creates the 7-pass rule for securely erasing disks. You could simply read the disk multiple times and get slightly different results with some statistical analysis and some cribs, you could at least partially reconstruction the original data. Today, magnetic disks have magnetic domains pretty much the same size as the head, and the servos are much more accurate. One pass erasing is sufficient. 27-pass is just a waste of time. Now for SSDs, you're just screwed.
- legodt 10y ago
  Could you please elaborate on your SSD comment? I'm interested to hear more.
  - theandrewbailey 10y ago
    SSD wear leveling algorithms ensure that the entire disk is used evenly. Any block on the drive can be literally anywhere in the storage medium, even more so than with hard drives. Some SSDs have significantly more storage media than they report (over-provisioning), again for wear leveling. In theory, SSD erasing is solved by TCG OPAL functionality. All data written to the disk medium is encrypted, whether or not it is taken advantage of by the user. The key it uses cannot be retrieved or set by the user. Tell the disk to change the key it uses and the entire device is unintelligible noise. Some articles: http://www.techrepublic.com/article/erasing-ssds-security-is-an-issue/ http://www.techrepublic.com/article/erasing-ssds-security-is... http://arstechnica.com/security/2011/03/ask-ars-how-can-i-safely-erase-the-data-from-my-ssd-drive/ http://arstechnica.com/security/2011/03/ask-ars-how-can-i-sa...
    - flyinghamster 10y ago
      Shouldn't the ATA Secure Erase command take care of properly blanking an SSD? (Assuming that its firmware can be trusted, of course.) In practice, it's a bit more complicated, though - typically the BIOS (or is the operating system?) locks out Secure Erase and you have to hot-remove the drive and reconnect it before the drive will accept it.
      - bitwize 10y ago
        > Shouldn't the ATA Secure Erase command take care of properly blanking an SSD? (Assuming that its firmware can be trusted, of course.) It does that -- by clobbering the hw encryption key.

by Nr7 10y ago

jonathankoren 10y ago

This worked because the magnetic domains on the disk were larger than the r/w head on drive, and due to play in the servo mechanism. It's the same reason why the DOD creates the 7-pass rule for securely erasing disks. You could simply read the disk multiple times and get slightly different results with some statistical analysis and some cribs, you could at least partially reconstruction the original data. Today, magnetic disks have magnetic domains pretty much the same size as the head, and the servos are much more accurate. One pass erasing is sufficient. 27-pass is just a waste of time. Now for SSDs, you're just screwed.

legodt 10y ago
Could you please elaborate on your SSD comment? I'm interested to hear more.
- theandrewbailey 10y ago
  SSD wear leveling algorithms ensure that the entire disk is used evenly. Any block on the drive can be literally anywhere in the storage medium, even more so than with hard drives. Some SSDs have significantly more storage media than they report (over-provisioning), again for wear leveling. In theory, SSD erasing is solved by TCG OPAL functionality. All data written to the disk medium is encrypted, whether or not it is taken advantage of by the user. The key it uses cannot be retrieved or set by the user. Tell the disk to change the key it uses and the entire device is unintelligible noise. Some articles: http://www.techrepublic.com/article/erasing-ssds-security-is-an-issue/ http://www.techrepublic.com/article/erasing-ssds-security-is... http://arstechnica.com/security/2011/03/ask-ars-how-can-i-safely-erase-the-data-from-my-ssd-drive/ http://arstechnica.com/security/2011/03/ask-ars-how-can-i-sa...
  - flyinghamster 10y ago
    Shouldn't the ATA Secure Erase command take care of properly blanking an SSD? (Assuming that its firmware can be trusted, of course.) In practice, it's a bit more complicated, though - typically the BIOS (or is the operating system?) locks out Secure Erase and you have to hot-remove the drive and reconnect it before the drive will accept it.
    - bitwize 10y ago
      > Shouldn't the ATA Secure Erase command take care of properly blanking an SSD? (Assuming that its firmware can be trusted, of course.) It does that -- by clobbering the hw encryption key.