On Fri, 07 Jul 2006 16:23:31 -0700, "John Hurliman" <[EMAIL PROTECTED]>
said:
> The UpdateInventoryItem packet contains a CRC that, according to
> Phoenix Linden is "made up of a couple of the other fields". Through
> trial and error we've discovered it is affected by at least some of
> the UUIDs and permission masks, but not the name or description. Our
> best guess is that this is a CRC-32, but we've found no evidence to
> support this guess, it could just as easily be a homebrewed CRC
> algorithm. Code or pseudocode to generate this one field nets $150
> through PayPal.
For the big bucks:
General idea: add together a bunch of 32-bit little-endian numbers (with
one exception) and there you go
pseudo-Cish code: (assuming all of the non-UUID values are already
correctly stored in the correct-endian format, of course)
unsigned int LLUUID_crc(byte uuid[16]) {
unsigned int retval=0;
retval+= (uuid[3]<<24+uuid[2]<<16+uuid[1]<<8+uuid[0]);
retval+= (uuid[7]<<24+uuid[6]<<16+uuid[5]<<8+uuid[4]);
retval+= (uuid[11]<<24+uuid[10]<<16+uuid[9]<<8+uuid[8]);
retval+= (uuid[15]<<24+uuid[14]<<16+uuid[13]<<8+uuid[12]);
return retval;
}
unsigned int CRC=0; // 32 bits!
/* IDs */
CRC += LLUUID_crc(AssetID);
CRC += LLUUID_crc(FolderID);
CRC += LLUUID_crc(ItemID);
/* Permission stuff */
CRC += LLUUID_crc(CreatorID);
CRC += LLUUID_crc(OwnerID);
CRC += LLUUID_crc(GroupID);
/* CRC += another 4 words which always seem to be zero -- unclear if
this
is a LLUUID or what */
CRC += owner_mask; /* Either owner_mask or next_owner_mask
may need to be */
CRC += next_owner_mask; /* switched with base_mask -- 2 values go
here and in my */
CRC += everyone_mask; /* study item, the three were identical.
*/
CRC += group_mask;
/* other, uh, stuff */
CRC += flags;
CRC += (unsigned int)inv_type;
CRC += (unsigned int)type; // watch out for sign extension
here --
CRC += (unsigned int)creation_date; // all of these values are
internally stored
CRC += (unsigned int)sale_price; // as 32-bit numbers
CRC += (unsigned int)(sale_type* 0x07073096); /* this looks like some
sort of attempt at
an actual CRC32 -- it
comes from the table
but the first 4 bits
are zero -- odd */
So, to be clear here, the "CRC" is calculated by simple addition, with
only one value being multiplied.
As a double-check, let's match this up against the packet:
Low 00321 - UpdateInventoryItem - Untrusted - Unencoded
0065 InventoryData (Variable)
0047 GroupOwned (BOOL / 1) (unused)
0149 CRC (U32 / 1) (n/a)
0159 CreationDate (S32 / 1) (used, as unsigned -- may not
matter)
0345 SaleType (U8 / 1) (used, but multiplied by
0x07073096)
0395 BaseMask (U32 / 1) (may be used? see above)
0506 Name (Variable / 1) (not used.)
0562 InvType (S8 / 1) (used, but as a U32)
0630 Type (S8 / 1) (used, but as a U32)
0680 AssetID (LLUUID / 1) (broken up into U32s and added)
0699 GroupID (LLUUID / 1) (ditto)
0716 SalePrice (S32 / 1) (used as a U32)
0719 OwnerID (LLUUID / 1) (as above)
0736 CreatorID (LLUUID / 1) (as above)
0968 ItemID (LLUUID / 1) (as above)
1025 FolderID (LLUUID / 1) (as above)
1084 EveryoneMask (U32 / 1) (used)
1101 Description (Variable / 1) (not used)
1189 Flags (U32 / 1) (used)
1348 NextOwnerMask (U32 / 1) (used)
1452 GroupMask (U32 / 1) (used)
1505 OwnerMask (U32 / 1) (used)
Either BaseMask, GroupMask or OwnerMask is thrown away -- not clear from
above. I didn't see GroupOwned being used, but it could be in the zero
bytes I mentioned.
Ben
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