Re: Embedding a Checksum in an Image File

From	Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups	comp.arch.embedded
Subject	Re: Embedding a Checksum in an Image File
Date	2023-04-20 12:14 +0300
Organization	Tidorum Ltd
Message-ID	<kace4iFke6vU1@mid.individual.net> (permalink)
References	<116ff07e-5e25-469a-90a0-9474108aadd3n@googlegroups.com>

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On 2023-04-20 5:06, Rick C wrote:
> This is a bit of the chicken and egg thing.  If you want a embed a
> checksum in a code module to report the checksum, is there a way of
> doing this?  It's a bit like being your own grandfather, I think.
> 
> I'm not thinking anything too fancy, like a CRC, but rather a simple
> modulo N addition, maybe N being 2^16.

Some decades ago I was involved with a project for an 8052-based device, 
which was required to perform a code-check-sum check at boot.

We decided to use a byte-per-byte xor checksum and make the correct 
check-sum be zero. We had a code module (possibly in assembler, I don't 
remember) that defined a one-byte "adjustment" constant in code memory. 
For each new version of the code, we first set the adjustment constant 
to zero, then ran the program, and it usually reported an error at boot 
because the check-sum was not zero. We then changed the adjustment 
constant to the actual reported checksum, C say, and that zeroed the 
check-sum because C xor C = 0. Bingo. You can use this method to make 
the checksum anything you like, for example hex 55.

With a more advanced order-sensitive check-sum such as a CRC you could 
use the same method if you also ensure (by linker commands) that the 
adjustment value is always the last value that enters in the computed 
check-sum (assuming that the linking order of the other code modules is 
not incidentally changed when the value of the adjustment constant is 
changed).

Thread

Embedding a Checksum in an Image File Rick C <gnuarm.deletethisbit@gmail.com> - 2023-04-19 19:06 -0700
  Re: Embedding a Checksum in an Image File Niklas Holsti <niklas.holsti@tidorum.invalid> - 2023-04-20 12:14 +0300
    Re: Embedding a Checksum in an Image File Rick C <gnuarm.deletethisbit@gmail.com> - 2023-04-20 06:18 -0700
  Re: Embedding a Checksum in an Image File "Peter Heitzer" <peter.heitzer@rz.uni-regensburg.de> - 2023-04-20 11:30 +0000
  Re: Embedding a Checksum in an Image File dalai lamah <antonio12358@hotmail.com> - 2023-04-20 13:47 +0200
    Re: Embedding a Checksum in an Image File Rick C <gnuarm.deletethisbit@gmail.com> - 2023-04-20 06:04 -0700
  Re: Embedding a Checksum in an Image File David Brown <david.brown@hesbynett.no> - 2023-04-20 16:46 +0200
  Re: Embedding a Checksum in an Image File George Neuner <gneuner2@comcast.net> - 2023-04-20 11:33 -0400
    Re: Embedding a Checksum in an Image File Rick C <gnuarm.deletethisbit@gmail.com> - 2023-04-20 09:45 -0700
      Re: Embedding a Checksum in an Image File David Brown <david.brown@hesbynett.no> - 2023-04-20 22:26 +0200
        Re: Embedding a Checksum in an Image File Ulf Samuelsson <ulf.r.samuelsson@gmail.com> - 2023-04-27 18:36 +0200
          Re: Embedding a Checksum in an Image File David Brown <david.brown@hesbynett.no> - 2023-04-28 09:12 +0200
            Re: Embedding a Checksum in an Image File Ulf Samuelsson <ulf.r.samuelsson@gmail.com> - 2023-04-28 10:35 +0200
      Re: Embedding a Checksum in an Image File George Neuner <gneuner2@comcast.net> - 2023-04-20 16:44 -0400
        Re: Embedding a Checksum in an Image File Don Y <blockedofcourse@foo.invalid> - 2023-04-20 22:37 -0700
          Re: Embedding a Checksum in an Image File David Brown <david.brown@hesbynett.no> - 2023-04-21 12:43 +0200
            Re: Embedding a Checksum in an Image File Don Y <blockedofcourse@foo.invalid> - 2023-04-21 04:39 -0700
              Re: Embedding a Checksum in an Image File David Brown <david.brown@hesbynett.no> - 2023-04-21 16:50 +0200
                Re: Embedding a Checksum in an Image File Don Y <blockedofcourse@foo.invalid> - 2023-04-21 17:29 -0700
                Re: Embedding a Checksum in an Image File David Brown <david.brown@hesbynett.no> - 2023-04-22 16:57 +0200
                Re: Embedding a Checksum in an Image File Don Y <blockedofcourse@foo.invalid> - 2023-04-24 00:32 -0700
                Re: Embedding a Checksum in an Image File David Brown <david.brown@hesbynett.no> - 2023-04-24 16:37 +0200
                Re: Embedding a Checksum in an Image File Don Y <blockedofcourse@foo.invalid> - 2023-05-03 00:15 -0700
                Re: Embedding a Checksum in an Image File David Brown <david.brown@hesbynett.no> - 2023-05-03 14:48 +0200
                Re: Embedding a Checksum in an Image File Ulf Samuelsson <ulf.r.samuelsson@gmail.com> - 2023-05-09 20:42 +0200
                Re: Embedding a Checksum in an Image File David Brown <david.brown@hesbynett.no> - 2023-05-10 10:06 +0200
                Re: Embedding a Checksum in an Image File Ulf Samuelsson <ulf.r.samuelsson@gmail.com> - 2023-05-10 12:03 +0200
                Re: Embedding a Checksum in an Image File Don Y <blockedofcourse@foo.invalid> - 2023-08-05 01:48 -0700
                Re: Embedding a Checksum in an Image File Don Y <blockedofcourse@foo.invalid> - 2023-08-05 01:42 -0700
        Re: Embedding a Checksum in an Image File Stefan Reuther <stefan.news@arcor.de> - 2023-04-21 19:40 +0200
    Re: Embedding a Checksum in an Image File Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2023-04-20 20:17 +0300
      Re: Embedding a Checksum in an Image File George Neuner <gneuner2@comcast.net> - 2023-04-20 16:49 -0400
  Re: Embedding a Checksum in an Image File Richard Damon <Richard@Damon-Family.org> - 2023-04-20 22:09 -0400
    Re: Embedding a Checksum in an Image File Rick C <gnuarm.deletethisbit@gmail.com> - 2023-04-20 19:41 -0700
      Re: Embedding a Checksum in an Image File Richard Damon <Richard@Damon-Family.org> - 2023-04-21 19:30 -0400
  Re: Embedding a Checksum in an Image File Brian Cockburn <brian.cockburn.1959@gmail.com> - 2023-04-21 01:53 -0700
    Re: Embedding a Checksum in an Image File Rick C <gnuarm.deletethisbit@gmail.com> - 2023-04-21 05:12 -0700
      Re: Embedding a Checksum in an Image File David Brown <david.brown@hesbynett.no> - 2023-04-21 17:02 +0200
        Re: Embedding a Checksum in an Image File Brian Cockburn <brian.cockburn.1959@gmail.com> - 2023-04-21 16:56 -0700
          Re: Embedding a Checksum in an Image File David Brown <david.brown@hesbynett.no> - 2023-04-22 17:01 +0200
        Re: Embedding a Checksum in an Image File Rick C <gnuarm.deletethisbit@gmail.com> - 2023-04-21 20:14 -0700
          Re: Embedding a Checksum in an Image File David Brown <david.brown@hesbynett.no> - 2023-04-22 17:13 +0200
            Re: Embedding a Checksum in an Image File Rick C <gnuarm.deletethisbit@gmail.com> - 2023-04-22 09:56 -0700
              Re: Embedding a Checksum in an Image File David Brown <david.brown@hesbynett.no> - 2023-04-22 19:54 +0200
                Re: Embedding a Checksum in an Image File Grant Edwards <invalid@invalid.invalid> - 2023-04-22 20:05 +0000
                Re: Embedding a Checksum in an Image File David Brown <david.brown@hesbynett.no> - 2023-04-23 17:37 +0200
                Re: Embedding a Checksum in an Image File Grant Edwards <invalid@invalid.invalid> - 2023-04-23 17:37 +0000
                Re: Embedding a Checksum in an Image File David Brown <david.brown@hesbynett.no> - 2023-04-23 23:45 +0200
                Re: Embedding a Checksum in an Image File Richard Damon <Richard@Damon-Family.org> - 2023-04-23 18:16 -0400
                Re: Embedding a Checksum in an Image File David Brown <david.brown@hesbynett.no> - 2023-04-24 09:13 +0200
                Re: Embedding a Checksum in an Image File boB <boB@K7IQ.com> - 2023-04-22 13:41 -0700
                Re: Embedding a Checksum in an Image File Rick C <gnuarm.deletethisbit@gmail.com> - 2023-04-23 10:34 -0700
                Re: Embedding a Checksum in an Image File David Brown <david.brown@hesbynett.no> - 2023-04-23 23:58 +0200
                Re: Embedding a Checksum in an Image File Rick C <gnuarm.deletethisbit@gmail.com> - 2023-04-23 15:24 -0700
                Re: Embedding a Checksum in an Image File David Brown <david.brown@hesbynett.no> - 2023-04-24 09:17 +0200
                Re: Embedding a Checksum in an Image File Rick C <gnuarm.deletethisbit@gmail.com> - 2023-04-24 01:07 -0700
          Re: Embedding a Checksum in an Image File Ulf Samuelsson <ulf.r.samuelsson@gmail.com> - 2023-04-27 18:42 +0200
            Re: Embedding a Checksum in an Image File David Brown <david.brown@hesbynett.no> - 2023-04-28 09:20 +0200
              Re: Embedding a Checksum in an Image File Ulf Samuelsson <ulf.r.samuelsson@gmail.com> - 2023-04-28 10:44 +0200
      Re: Embedding a Checksum in an Image File Brian Cockburn <brian.cockburn.1959@gmail.com> - 2023-04-21 16:52 -0700
        Re: Embedding a Checksum in an Image File Rick C <gnuarm.deletethisbit@gmail.com> - 2023-04-21 20:23 -0700
          Re: Embedding a Checksum in an Image File Brian Cockburn <brian.cockburn.1959@gmail.com> - 2023-04-22 07:07 -0700
            Re: Embedding a Checksum in an Image File Richard Damon <Richard@Damon-Family.org> - 2023-04-22 10:31 -0400
            Re: Embedding a Checksum in an Image File Rick C <gnuarm.deletethisbit@gmail.com> - 2023-04-22 09:54 -0700
  Re: Embedding a Checksum in an Image File Ulf Samuelsson <ulf.r.samuelsson@gmail.com> - 2023-04-27 18:26 +0200
    Re: Embedding a Checksum in an Image File Rick C <gnuarm.deletethisbit@gmail.com> - 2023-04-27 10:09 -0700
      Re: Embedding a Checksum in an Image File Niklas Holsti <niklas.holsti@tidorum.invalid> - 2023-04-27 21:29 +0300
        Re: Embedding a Checksum in an Image File Niklas Holsti <niklas.holsti@tidorum.invalid> - 2023-04-27 21:39 +0300
        Re: Embedding a Checksum in an Image File Ulf Samuelsson <ulf.r.samuelsson@gmail.com> - 2023-04-27 22:44 +0200
          Re: Embedding a Checksum in an Image File David Brown <david.brown@hesbynett.no> - 2023-04-28 09:38 +0200
            Re: Embedding a Checksum in an Image File Ulf Samuelsson <ulf.r.samuelsson@gmail.com> - 2023-04-28 10:50 +0200
              Re: Embedding a Checksum in an Image File David Brown <david.brown@hesbynett.no> - 2023-04-28 15:04 +0200
                Re: Embedding a Checksum in an Image File Ulf Samuelsson <ulf.r.samuelsson@gmail.com> - 2023-04-29 23:03 +0200
                Re: Embedding a Checksum in an Image File David Brown <david.brown@hesbynett.no> - 2023-04-30 16:19 +0200
                Re: Embedding a Checksum in an Image File Ulf Samuelsson <ulf.r.samuelsson@gmail.com> - 2023-05-09 20:34 +0200
                Re: Embedding a Checksum in an Image File David Brown <david.brown@hesbynett.no> - 2023-05-10 10:18 +0200
        Re: Embedding a Checksum in an Image File David Brown <david.brown@hesbynett.no> - 2023-04-28 09:33 +0200
      Re: Embedding a Checksum in an Image File Ulf Samuelsson <ulf.r.samuelsson@gmail.com> - 2023-04-27 22:36 +0200
        Re: Embedding a Checksum in an Image File Niklas Holsti <niklas.holsti@tidorum.invalid> - 2023-04-28 01:10 +0300
          Re: Embedding a Checksum in an Image File Ulf Samuelsson <ulf.r.samuelsson@gmail.com> - 2023-04-28 10:54 +0200
    Re: Embedding a Checksum in an Image File David Brown <david.brown@hesbynett.no> - 2023-04-28 09:24 +0200
      Re: Embedding a Checksum in an Image File Ulf Samuelsson <ulf.r.samuelsson@gmail.com> - 2023-04-28 10:56 +0200
        Re: Embedding a Checksum in an Image File David Brown <david.brown@hesbynett.no> - 2023-04-28 15:09 +0200
          Re: Embedding a Checksum in an Image File Ulf Samuelsson <ulf.r.samuelsson@gmail.com> - 2023-04-29 23:02 +0200
  Re: Embedding a Checksum in an Image File Ulf Samuelsson <ulf.r.samuelsson@gmail.com> - 2023-04-27 18:27 +0200

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