checksum

I need to reverse engineer CRC/Checksum algorithm implemented by windows CE executable. Being propritory protocol, it does not say anything about CRC/checksum algorithm. However, There is console interface that reports correct/calculated checksum and I can construct my own messages with random bits if message protocol is correct: I have observed that, Changing single bit in message changes checksum bytes completely. Algorithm seems to be position dependent as I fed some single 1 bit messages in various message data positions with rest of the bits zero and all the time console reported

I'd like to calculate the checksum of an UDP header packet I want to send: packetosend = """60 00 00 00 00 24 3a 40 20 02 c0 a8 01 50 00 01 00 00 00 00 00 00 09 38 20 02 c0 a8 01 50 00 01 00 00 00 00 00 00 09 6f""" so I need to join this utf-16 (not a problem) and calculate the checksum of this specific packet. How can I do that? Thanks! EDIT: Yes it's an IPv6 header for an ICMPv6 packet, anyways what I would like to know is the formula, and how it works. I'll give another example with an ICMP ping echo (v4) packet: packet = """ 08 00 d1 15 76 0c 00 07 bf d3 55 4a ad b5 03 00 // "d1 15" is the

I need OpenCV3.0 since it supports some new functions which I need. I used the following code for installation (I had successfully installed OpenCV 2.4.9 using this code. But for OpenCV 3.0, while doing the cmake section, some error pops up due to mismatch of MD5 checksum) mkdir OpenCV cd OpenCV echo "Removing any pre-installed ffmpeg and x264" sudo apt-get -qq remove ffmpeg x264 libx264-dev echo "Installing Dependenices" sudo apt-get -qq install libopencv-dev build-essential checkinstall cmake pkg-config yasm libjpeg-dev libjasper-dev libavcodec-dev libavformat-dev libswscale-dev libdc1394-22

I need a C# .NET function to evaluate whether a typed or scanned barcode is a valid Global Trade Item Number (UPC or EAN). The last digit of a bar code number is a computer Check Digit which makes sure the bar code is correctly composed. GTIN Check Digit Calculator public static bool IsValidGtin(string code) { if (code != (new Regex("[^0-9]")).Replace(code, "")) { // is not numeric return false; } // pad with zeros to lengthen to 14 digits switch (code.Length) { case 8: code = "000000" + code; break; case 12: code = "00" + code; break; case 13: code = "0" + code; break; case 14: break; default

If a TCP payload gets corrupted in transit the recomputed checksum won't match the transmitted checksum. Great, all fine so far. If a TCP checksum gets corrupted in transit the recomputed checksum won't match the now corrupted checksum. Great, all fine so far. What happens when both the payload and checksum get corrupted and the recomputed checksum, whilst different to what it should be, just happens to match the now corrupted checksum? I can see with a good checksum algorithm (and additional checksums at lower levels) this might be very, very unlikely but isn't TCP meant to be 100% reliable?

My understanding is that a hash code and checksum are similar things - a numeric value, computed for a block of data, that is relatively unique. i.e. The probability of two blocks of data yielding the same numeric hash/checksum value is low enough that it can be ignored for the purposes of the application. So do we have two words for the same thing, or are there important differences between hash codes and checksums? I would say that a checksum is necessarily a hashcode . However, not all hashcodes make good checksums. A checksum has a special purpose --- it verifies or checks the integrity of

We perform checksums of some data in sql server as follows: declare @cs int; select @cs = CHECKSUM_AGG(CHECKSUM(someid, position)) from SomeTable where userid = @userId group by userid; This data is then shared with clients. We'd like to be able to repeat the checksum at the client end... however there doesn't seem to be any info about how the checksums in the functions above are calculated. Can anyone enlighten me? Dan On SQL Server Forum, at this page , it's stated: The built-in CHECKSUM function in SQL Server is built on a series of 4 bit left rotational xor operations. See this post for