Register to reply

Find a message given a CRC and generating polynomial

by JJBladester
Tags: generating, message, polynomial
Share this thread:
JJBladester
#1
Mar20-14, 07:17 PM
PF Gold
JJBladester's Avatar
P: 287
I am working on a circuit that inputs a 31-bit pseudo-random binary string into a CCIT CRC-16 block which generates a 16-bit CRC output.

I know that M(x)/G(x) = Q(x) + R(x) and the transmitted code will be R(x) appended to M(x).

When I simulated the circuit, I got a CRC of 1 0 1 0 1 0 0 1 0 0 0 0 0 0 0 0. From the help file of the software (VisSim/Comm), I know that the generating polynomial is G(x) = 1 0 0 0 1 0 0 0 0 0 0 1 0 0 0 1.

How do I determine the 31-bit input sequence that generated the CRC result?

Since M(x)/G(x) = Q(x) + R(x), we can say that M(x) = [Q(x) + R(x)]G(x). But we don't know Q(x). Assuming the 16-bit CRC is equal to R(x) and the G(x) is given, how do I go about finding M(x) without knowing Q(x)?
Phys.Org News Partner Engineering news on Phys.org
Hoverbike drone project for air transport takes off
Student develops filter for clean water around the world
Developing the next evolution in underwater communication
Baluncore
#2
Mar20-14, 09:16 PM
Sci Advisor
Thanks
P: 1,736
Because the generating polynomial is symmetrical = 1 0 0 0 1 0 0 0 0 0 0 1 0 0 0 1 you should be able to reverse the process in time without rewiring the generator.

First reverse the order of bits in your final CRC and load it into the generator. Then feed the data stream bits backward in time through the generator until you reach the original starting position.


Register to reply

Related Discussions
How do we assign a generator matrix for generating linear block codes from message ? Electrical Engineering 0
Derive Hermite Polynomial Generating Function from Recurrence Relation Calculus & Beyond Homework 0
How do you find the Probability Generating Function? Calculus & Beyond Homework 13
Find the curvature of the generating curve. Calculus & Beyond Homework 1
How to find pdf given moment generating function Set Theory, Logic, Probability, Statistics 1