====== Encrypted Disk System Support ======

//16 April 2002//

Added generic support for encrypted disk systems and added a few actual systems on the way. This requires data processing for mastering & saving of the disk(s), and data processing for [[:glossary:cta|analysation]] & viewing.

Since we are not altering the game code, we will not hardwire various encoders / decoders into the release format (they do not belong with the physical data). Once the data is checked, it should be represented in the format that is writeable and what the **unaltered** game expects - which is obviously the data in the original and encrypted form. However, for some formats we need the decrypted data for analysation and [[:article:importance of data integrity|integrity checks]], so that data should be produced as well.

===== New =====

Support for Rob Northen's encrypted disk format (RNDOS / PDOS) that have been seen on Team 17 and Probe titles so far, but quite possibly used on other games as well.

A decryption key is needed to decode the data [[:glossary:block|blocks]] and their parity information. We would hate to find this key manually for each title so a smart decoder phase was added that exploits a system flaw of each encryped system to obtain the required encryption key (or keys, should we find disks using more than one key, although this is unlikely).

The decryptor is treated as a data type. When the [[:glossary:cta|analyser]] encounters such data in the block descriptor, it finds out if the [[:glossary:track|track]] is actually one that can be decrypted using the method. Actual data is marked encrypted where applicable in the block descriptors, so the decoder can decrypt them before use.

The actual "Key" information is visibly displayed per-track for reference.

===== New Datatypes =====

  * RN Decryptor (see above)
  * MFM sync word, marker: a [[:glossary:sync|sync word]] that is not part of the logical data layout, but is used for other purposes like finding the first block on a track etc. The original [[:glossary:mfm|MFM]] sync word type is always part of the logical layout.
  * ADOS MFM long encoding: now supports additional processing (like decryption), and linear encoding of odd/even data bits as well as odd/even areas.
  * MFM gap size, byte: Size of MFM [[:glossary:gap|gap]] area. Support for gap scanning using this value, as a comparator (real gap count lesser or equal, greater or equal, or equal to the specified amount)

===== Games known to use these disk formats... =====

  * Team 17 developed/published titles
  * Probe titles
  * Red Baron
  * All Terrain Racing (as part of the [[:glossary:copy protection|protection]])
  * Quite possibly a lot more...