Calculating FCS for frame 802.11
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Thread: Calculating FCS for frame 802.11

  1. #1
    Join Date
    Jun 2010
    Posts
    4

    Calculating FCS for frame 802.11

    Hello,

    I'm trying to calculate FCS for 802.11 frame, I have the data, I know the data is corrupted because of WireShark is telling me. Also WireShark gives me the correct FCS value.So I wanted to calculate FCS by myself but I can't. I hope somebody can give me guide.

    Here's the code:

    Code:
    int main()
    {
    	unsigned char data[] = {0x00,0x00,0x14,0x00,0xee,0x18,0x00,0x00,0x10,0x02,0x85,
    							0x09,0xa0,0x00,0xa1,0x9c,0x0b,0x00,0x00,0x05,0x80,0x00,
    							0x00,0x00,0xff,0xff,0xff,0xff,0xff,0xff,0x00,0x15,0x70,
    							0x16,0x15,0x9c,0x00,0x15,0x70,0x16,0x15,0x9c,0xa0,0x6b,
    							0x9c,0xc1,0x96,0xe1,0x58,0x00,0x00,0x00,0x64,0x00,0x11,
    							0x20,0x00,0x0a,0x43,0x41,0x4d,0x50,0x55,0x53,0x2d,0x41,
    							0x49,0x52,0x01,0x08,0x82,0x84,0x8b,0x0c,0x12,0x96,0x18,
    							0x24,0x03,0x01,0x06,0x05,0x04,0x05,0x0a,0x00,0x00,0x07,
    							0x06,0x43,0xb9,0x72,0x01,0x0b,0x1e,0x2a,0x01,0x04,0x30,
    							0x14,0x01,0x00,0x00,0x0f,0xac,0x02,0x01,0x00,0x00,0x0f,
    							0xac,0x02,0x01,0x00,0x00,0x0f,0xac,0x01,0x01,0x00,0x32,
    							0x04,0x30,0x48,0x60,0x6c,0xad,0x0f,0x00,0xa0,0xf8,0x00,
    							0x00,0x00,0x00,0x01,0x00,0x00,0x00,0x47,0x65,0x28,0x4c,
    							0xdd,0x18,0x00,0x50,0xf2,0x01,0x01,0x00,0x00,0x50,0x41,
    							0x03,0x67,0x03,0x00,0x50,0xf2,0x02,0x01,0x00,0x00,0x50,
    							0xf2,0x01,0x00,0x00,0xdd,0x10,0x00,0xa0,0xf8,0x01,0x00,
    							0x01,0x0c,0x00,0x00,0x00,0x00,0xa0,0xf8,0x65,0xa9,0x0b,
    							0xab,0x93,0x8e,0x88};
    
    
    	unsigned int len = 191;
    
    	unsigned int crc = 0;
    
    	//calculate crc of the first byte until 191-4byes.
    	//because the last 4 bytes are reserved for FCS
    
    	//it should give us 0xee03cb23
    	printf("%02x\n", crc);
    
    
    	return 0;
    
    }
    I tried all CRC32, FCS32 and haven't been able to get this "0xee03cb23". This value comes from WireShark so I'm pretty sure about the CRC value.

    Can somebody tell me what's the step to calculate the CRC for 802.11 frame?


    Thanks
    Memphis

  2. #2
    Join Date
    Jun 2010
    Posts
    4

    Re: Calculating FCS for frame 802.11

    Seriously, nobody knows anything about FCS or how to calculate CRC32 for 802.11 frames?

    If you have even a small hint let me know.

    Thanks in advanced,

    Memphis

  3. #3
    Join Date
    Feb 2005
    Posts
    2,160

    Re: Calculating FCS for frame 802.11

    Seriously, did you try google? There's only about 596000 hits. I hope you not trying to spoof packets. That's against the forum rules.

  4. #4
    Join Date
    Jun 2010
    Posts
    4

    Re: Calculating FCS for frame 802.11

    Wow seriously, I'm disappointed from your answer. I don't understand, if you don't know the answer why did you post non-sense sentences. I knew the fourm rules, I know my position.
    And for your INFORMATION, All of these are standard and OPEN. everybody can use frame 802.11. I'm asking HOW CAN I CALCULATE FCS? What on earth did you think? Am I going to spoof Frames? come on man give me a break.

    Please people, this is a technical forum not other things, if you don't know the answer please, please don't post anything.

    One more thing, I did search, I did all the methods, I did re-write CRC32 but I'm not be able to get the same FCS result as wireshark does. I never post a subject until I have no answer.

    Thanks,
    Memphis
    Last edited by memphis.ray; June 29th, 2010 at 09:35 PM.

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