added notes about CroSys. blocksize. notes about encryption

1 files changed, 27 insertions, 3 deletions

diff --git a/docs/cronos-research.md b/docs/cronos-research.md
index a60d054..d076f0f 100644
--- a/docs/cronos-research.md
+++ b/docs/cronos-research.md
@@ -13,12 +13,19 @@ and a Vocabulary database with another set of these files in a sub directory Voc
 
 `CroIndex.*` can be ignored, unless we suspect there to be residues of old data. All words are serialized in little endianess.
 
+Additionally there are the `CroSys.dat` and `CroSys.tad` files in the cronos application directory, which list the currently
+known databases.
+
+## app installation
+
 On a default Windows installation, the CronosPro app shows with several encoding issues that can be fixed like this: 
 
     reg set HKLM\System\CurrentControlSet\Control\Nls\Codepage 1250=c_1251.nls 1252=c_1251.nls
 
 [from](https://ixnfo.com/en/question-marks-instead-of-russian-letters-a-solution-to-the-problem-with-windows-encoding.html)
 
+Also note that the v3 cronos app will run without problem on a linux machine using [wine](https://winehq.org/)
+
 ##Files ending in .dat
 
 All .dat files start with a 19 byte header:
@@ -26,9 +33,13 @@ All .dat files start with a 19 byte header:
     char      magic[9]      // allways: 'CroFile\x00'
     uint16    unknown
     char      version[5]    // 01.02, 01.03, 01.04
-    uint16    encoding      // 1 = KOD, 3 = encrypted
-    uint16    blocksize     // 0040 = Bank, 0400 = Index, 0200 = Stru
-    
+    uint16    encoding      // 0 or 2 = plain, 1 = KOD, 3 = encrypted
+    uint16    blocksize     // 0x0040, 0x0200 or 0x0400
+
+Most Bank files use blocksize == 0x0040
+most Index files use blocksize == 0x0400
+most Stru files use blocksize == 0x0200
+
 This is followed by a block of 0x101 or 0x100 minus 19 bytes seemingly random data.
 
 The unknown word is unclear but seems not to be random, might be a checksum.
@@ -140,6 +151,8 @@ The original description of an older database format called the per block counte
 In noticed that the first 256 bytes of CroStru.dat look close to identical (except the first 16 bytes) than CroBank.dat.
 
 
+The toplevel table-id for CroStru and CroSys is #3, while referenced records have tableid #4.
+
 ##CroBank
 
 CroBank.dat contains the actual database entries for multiple tables as described in the CroStru file. After each chunk is re-assembled (and potentially decoded with the per block offset being the record number in the .tad file).
@@ -204,3 +217,14 @@ some records are compressed, the format is like this:
     uint8   compdata[size-4]
     uint8   tail[3] = { 0, 0, 2 }
 
+## encrypted records
+
+In files with encoding type #3, records are encrypted.
+
+Several things observed:
+ * in encrypted .dat files, the first record starts at 0x100, instead of the usual 0x101
+ * probably with a fixed key, and no IV. This is likely so because I found several unrelated files where the
+   start of the encrypted data is the same for the first +- bytes.
+ * likely a stream of cipherdata xorred with the plaintext, since I found several records which differ in only a few bits.
+ * so probably: rc4.
+