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Regarding checksum calculation

Naveen Koneti
Greenhorn

Joined: Apr 27, 2007
Posts: 13
Hi in my project we are calculating the checksum using MD5 algorithm.The problem is the order of updation of the message digest is changing with this I am getting the different checksum for the same data.Is there any way to get same checksum irrespective of order of addition to the message digest.
William Brogden
Author and all-around good cowpoke
Rancher

Joined: Mar 22, 2000
Posts: 12675
    
    5
If you are getting different checksums, SOMETHING is different - either in the data or the way you are doing the checksums.

What do you mean about "the order of updation of the message digest"? You can't expect MD5 to give the same result with different order of data items - only the simplest checksum algorithms would do that.

I suppose you could calculate a message digest for each independent data item and find a way to combine them that does not depend on the order.

Bill


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Henry Wong
author
Sheriff

Joined: Sep 28, 2004
Posts: 18108
    
  39

You can't expect MD5 to give the same result with different order of data items - only the simplest checksum algorithms would do that.


A *checksum* algorithm will actually do that -- meaning take the sum and check it. Add all the characters together to form the checksum. This algorithm will not care about order since addition doesn't care about order.

Henry


Books: Java Threads, 3rd Edition, Jini in a Nutshell, and Java Gems (contributor)
 
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