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NowSMS Support Forums ⬆ NowSMS Support - MMS & Advanced Issues ⬆ Archive through July 28, 2006 ⬆ |
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| Author | Message | |||
| Ben Wilson New member Username: Bmwilson Post Number: 6 Registered: 11-2003 |
Hi Bryce, I've noticed some discrepancies between the SD files that DRMCOMP produces vs. what Nokia's Mobile Internet Toolkit does even if all the headers are set identically. If the input file size is a multiple of 16-bytes (128-bits) then DRMCOMP produces a file of exactly the same length as NMIT does. If the input file size isn't a multiple of 16-bytes then DRMCOMP's dcf file is a different length than NMIT's. I think it has to do with the padding used in the AES encryption as AES is based on a 128-bit block size. An example: If I take a 136 byte file and encode it with NMIT it comes out to say 260 bytes but DRMCOMP's comes out at 252 bytes. The missing 8 bytes could be due to that 136 bytes isn't a multiple of 16 bytes (128-bits) and so NMIT is padding it's input file up to 144 bytes to get to the nearest greater multiple. So then 144 - 136 = 8 bytes. Having seen problems with how fussy mobile phones can be with reading Forward-Lock and Combined Delivery, I'm just wondering if this will cause problems on some phones? Which is the 'correct' implementation? Thanks and best regards, Ben. | |||
| Bryce Norwood - NowSMS Support Board Administrator Username: Bryce Post Number: 5679 Registered: 10-2002 |
Hi Ben, Have you tried the updated DRMCOMP? (Referenced in the following thread http://support.nowsms.com/discus/messages/485/14341.html) The original version did have a problem with input files that are not on a 16 byte boundary, in that we neglected to use padding. (That is the error that I mention at the bottom of that thread.) We refereshed the download to include a newer DRMCOMP.EXE after I posted my response on that thread. So check the file date on DRMCOMP.EXE, and if it is prior to 2006-03-14, then re-download the trial version installer to get an updated version. It's a little confusing because the version number of NowSMS still says 2006.03.09 (for March 9, 2006), but we did refresh the install to include a DRMCOMP.EXE with a file date of 2006-03-14. The updated DRMCOMP uses the correct padding. (We probably could have stuck to the previous behavior, but modified the headers to specify that no padding was used ... but we were hesitant to do this as we feared it might not be as widely supported.) -bn | |||
