Synopsis
I calculate CRC32 of few hex inputs using :
http://www.sunshine2k.de/coding/javascript/crc/crc_js.html
and few other CRC32 calculators.
Problem
Whatever the input i give, i get the same CRC32:
aa aa 3 0 0 0 8 0 45 0 0 34 0 0 40 0 40 6 b7 e c0 a8 1 64 c0 a8 1 1 dd 95 0 50 f4 11 d8 cf 81 8e e5 e3 80 10 10 0 d6 4c 0 0 1 1 8 a f a7 bf e0 0 0 2a f9 da b3 91 bd
Result CRC value: 0x2144DF1C
aa aa 3 0 0 0 86 dd 60 0 77 b0 1 49 11 ff fe 80 0 0 0 0 0 0 0 2 b9 df 87 1b 9a 36 ff 2 0 0 0 0 0 0 0 0 0 0 0 0 0 fb 14 e9 14 e9 1 49 36 d5 0 0 0 0 0 11 0 0 0 0 0 1 8 5f 61 69 72 70 6c 61 79 4 5f 74 63 70 5 6c 6f 63 61 6c 0 0 c 0 1 5 5f 72 61 6f 70 c0 15 0 c 0 1 8 5f 61 69 72 70 6f 72 74 c0 15 0 c 0 1 7 5f 75 73 63 61 6e 73 c0 15 0 c 0 1 8 5f 73 63 61 6e 6e 65 72 c0 15 0 c 0 1 6 5f 75 73 63 61 6e c0 15 0 c 0 1 7 5f 69 70 70 75 73 62 c0 15 0 c 0 1 4 5f 69 70 70 c0 15 0 c 0 1 5 5f 69 70 70 73 c0 15 0 c 0 1 8 5f 70 72 69 6e 74 65 72 c0 15 0 c 0 1 f 5f 70 64 6c 2d 64 61 74 61 73 74 72 65 61 6d c0 15 0 c 0 1 4 5f 70 74 70 c0 15 0 c 0 1 d 5f 61 70 70 6c 65 2d 6d 6f 62 64 65 76 c0 15 0 c 0 1 8 39 30 65 33 30 37 66 63 4 5f 73 75 62 e 5f 61 70 70 6c 65 2d 6d 6f 62 64 65 76 32 c0 15 0 c 0 1 f 5f 61 70 70 6c 65 2d 70 61 69 72 61 62 6c 65 c0 15 0 c 0 1 c0 e1 0 c 0 1 c 5f 73 6c 65 65 70 2d 70 72 6f 78 79 4 5f 75 64 70 c0 1a 0 c 0 1 0 0 29 5 a0 0 0 11 94 0 c 0 4 0 8 0 c e0 ac cb 92 66 48 c2 43 4c 9f
Result CRC value: 0x2144DF1C
aa aa 3 0 0 0 8 0 45 0 0 34 0 0 40 0 40 6 b7 e c0 a8 1 64 c0 a8 1 1 dd 8f 0 50 f ff 68 34 80 1c a4 f9 80 10 10 10 73 b8 0 0 1 1 8 a f a7 ba c 0 0 2a 62 e1 2d 8a cd
Result CRC value: 0x2144DF1C
Question
Why is this happening ?
The CRC is a constant because the last 4 bytes of the message are the CRC for all but the last 4 bytes of the message. The CRC is a non-zero constant, in this case, 0x2144DF1C, because the CRC is being post complemented (final xor value = 0xFFFFFFFF). You'll get the same result (0x2144DF1C) for a 4 byte message of all zeroes:
00 00 00 00
What happens is the 4 bytes of zeroes are xor'ed with the initial value 0xFFFFFFFF, and then CRC is calculated for {FF FF FF FF}, resulting in 0xDEBB20E3, which is post complemented (final xor value = 0xFFFFFFFF) to get 0x2144DF1C .
To show a case where the CRC ends up = 0, I complemented the last 4 bytes (the message CRC) in the first and last examples. If you choose CRC32, then click on custom, then set final xor value = 0, you'll get CRC = 0 for these two examples:
aa aa 3 0 0 0 8 0 45 0 0 34 0 0 40 0 40 6 b7 e c0 a8 1 64 c0 a8 1 1 dd 95 0 50 f4 11 d8 cf 81 8e e5 e3 80 10 10 0 d6 4c 0 0 1 1 8 a f a7 bf e0 0 0 2a f9 25 4c 6e 42
aa aa 3 0 0 0 8 0 45 0 0 34 0 0 40 0 40 6 b7 e c0 a8 1 64 c0 a8 1 1 dd 8f 0 50 f ff 68 34 80 1c a4 f9 80 10 10 10 73 b8 0 0 1 1 8 a f a7 ba c 0 0 2a 62 1e D2 75 32