[Windows Phone 7 Development and Hacking] GoodDayToDie:
Analysis of the policy database

I wrote a function to dump the policy database to a text file (with inevitably some embedded binary). Each record in the database has four fields. I'll do my best to describe them below.

1) The first is a DATETIME struct (two 32-bit integers). This is the only 64-bit numerical type available except for a DOUBLE, so it might be selected just as a convenient way to store that many bits rather than because it's actually a date and time. In particular, when I converted them to actual dates and times, the years ranged from the 1970s well into future centuries... this seems an unlikely candidate for an actual set of dates.

What I think it actually is, is some kind of hash of the second field. It might be the index bits for the bloom filter, for example. The reason I think so is that, when there are multiple records with the same value in the second field, they also have the same value in this field, but even a slight difference in the value of the second field results in a very different first field.

This field is not unique, but it does appear to be the default sort order for the database. I don't know if that's ust because it's the first field, but it would make sense to have it be indexed using this field for fast lookup (binary search) after the bloom filter finds that the item is (probably) present.

2) This field is a binary BLOB struct (a size and a pointer). This field contains Unicode strings, sometimes with a bit of binary data (small, typically less than 20 bytes) tacked on the end. Strings plural; each one is NULL-character terminated.

This field appears to be the paths that indicate the object (or objects, since it can contain wildcards) that the policy applies to. If there is a policy in the XML for ResourceIri="/REGISTRY/HKLM/SOFTWARE/MICROSOFT/CAMERA/READWRITESETTINGS" then there will be a record in the database with the second field that would be written like this in C source code: L"REGISTRY\0HKLM\0SOFTWARE\0MICROSOFT\0CAMERA\0READWRITESETTINGS\0". I'm not sure what the occasional binary afterwards means, although there appears to be a specific value for a wildcard (represented in the source XML as ResourceIri=/PATH/WILDCARD/BASE/(*)", but the last part doesn't translate to Unicade the way you'd expect).

As mentioned above, I'm pretty sure that the first field is related to this one. Since the value of a bloom filter on this database would be to quickly establish "Is there a policy for this object?" it makes sense that the path (second field) is the data that gets hashed to produce the bits of the key. It's not really required to then store the key bits, but they make a reasoanble value to sort on.

3) The third field is also a binary BLOB, but the value of it is much more opaque. Typically in the range of 50-300 bytes in length, there are certain patterns that I've noticed within it (0x01 00 01/02 00 65 is a common prefix, and they typically end with 0x00 3X) but I have not yet determined what they actually represent.

Some logical possibilities are an account identifier (though that seems needlessly long for such a purpose) or possibly the permissions data directly. When the second field has a path to related objects (for example, the isolated storage of an application), the third field is often similar as well.

4) The fourth field is another DATETIME struct, but in this case is obviously not an actual date value. The high four bytes are (almost?) always 0xFFFFFFFC, and the low four bytes are typically 0x0000XXXX where the Xs can be anything. This value is not unique - there are numerous instances of 0xFFFFFFFC00000001, for example - but I'm not yet sure what it is.

The same guesses I offered for field 3 apply as well, with the caveat that it's probably not just a different representation of field 3 because two records can have the same value on field 4, and their field three values may not only differ, but be different sizes. I need to look at the XML files and see if there's a pattern between policies with the same field 4 and an equivalent data item in the XML.

I'm attaching the dump file I created of the policy database. It's best opened in a hex editor (Visual Studio does well enough) although you can also use Wordpad (Notepad won't respect the line endings). Wordpad can't show you the binary, of course, but it's a readable layout of the data.

The format is as follows:

ASCII string: "Index "

ASCII representation of an Integer for the index.

ASCII string: ": Prop0 (FILETIME): 0x"

ASCII representation of the DateTime, with a space between the high and low DWORDs.

ASCII string: " | Prop1 (BLOB, "

ASCII representation of the blob's integer size.

ASCII string: " bytes): "

Direct dump of the second field's BLOB buffer (multiple UNICODE strings).

ASCII string: " | Prop2 (BLOB, "

... and so on. I intentionally used ASCII to make the direct memory dumps, which are in UNICODE for the second field at least, stand out.