Saturday, 1 June 2013

Can i modify data "protected" by a CRC16?

Can i modify data "protected" by a CRC16?

There are 100 bytes with a CRC16. However I only know the first 50.
I want to change byte 5 from a known value X to another value Y, and fix up the CRC16 to be valid - without knowing bytes 50-100.
This is possible with the TCP checksum, because it's just addition. But CRC16 is a polynomial. Is it still possible?

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