Calculate Checksum

**Ming** · 24-12-2002, 07:22 AM

Can anyone give me a brief tutorial on how to calculate checksums? I did some changes with my N3350 with ppmedit and I tried to fixed the checksum with NFree1.3 but it failed. I flash the file to my phone but it ends up no networks and auto off/on. I duno whether if theres a program out there that can fixed this problem or the checksum so I decided instead of waiting, I can use some time to learn how to do it by myself. So my brain is urs! Hah!

**optimus777** · 24-12-2002, 08:33 AM

Try use Genolite 1.6 or 1.7
or just check killer & check Fixer

Kill MCU+PPM checksum....

**Ming** · 25-12-2002, 06:49 AM

Rite! So where can I download this software? Actually I would like to know the concept of how to calculate the checksum. Why is it checksum is important. I would wanna get more detail on this. Any help? Thanks Optimus777.

**Kontact** · 25-12-2002, 08:37 AM

the way i recall it. chksum (last 4 bytes) is calculated like this.

it starts at 0x40 upto the end of the mcu/ppm.

it gets 2 bytes on every 0x20. so if it start 0x40 next will be 0x60 and so on.

it uses, a modified md5 algorithm. (looks like)

if u r interested try d/l the fchk_c on the download section of nokiafree.org and try to analyze it.

hope this help.

regards,

**atlantiscd** · 25-12-2002, 02:01 PM

Isn't checksum calculated like this?

function to calculate checksum byte
---------------------------------------------
Function calcCheckSum(SendBuffer)
CheckSum = Asc(Left(SendBuffer, 1))
For i = 2 To Len(SendBuffer)
CheckSum = CheckSum Xor Asc(Mid(SendBuffer, i, 1))
Next
calcCheckSum = Chr(CheckSum)
End Function

-------------------
/Atlantis

**Kontact** · 25-12-2002, 02:39 PM

oopp.. i think "ming" could be asking abut mcu and ppm (7-8 section chksums). since he mention nfree.

with mcu chksum killer. mcu chksum (16 bits) is now kind of obsolite. but ppm section we still need to calc each 32bit checksums. to avoid contact service.

for ex. on the ppm section the first section is LPCS.

if u try to look at 3310v559 A. using hex editor. go to loc 0x2c. the 32bit there is 0xE18247C7. (this is the 32bit checksum of ppm LPCS.)
after that is the length 0x00000234. what u do is add it in 32 bits upto the 0x234 length. and u will get the 32bits chksum.

do this till u reach the 7-8 ppm sections. depends on what kind of dct3. 5110 has 7 ppm sections while other have 8 ppm sections.

the one i talk about in my previous message is about the faid chksums.

regards,