Advertisement
If you have a new account but are having problems posting or verifying your account, please email us on hello@boards.ie for help. Thanks :)
Hello all! Please ensure that you are posting a new thread or question in the appropriate forum. The Feedback forum is overwhelmed with questions that are having to be moved elsewhere. If you need help to verify your account contact hello@boards.ie
Hi there,
There is an issue with role permissions that is being worked on at the moment.
If you are having trouble with access or permissions on regional forums please post here to get access: https://www.boards.ie/discussion/2058365403/you-do-not-have-permission-for-that#latest

Checksum in a Data

  • 22-02-2011 12:55pm
    #1
    RealistSpy
    Registered Users, Registered Users 2 Posts: 1,686 ✭✭✭


    Hi,

    I hope this is the right place to post this but here is a scenario.

    I have a data but every time I modify the data in anyway the data gets corrupted. The data has a crc32 security.

    Is there anyways I can find out the crc32 offset in the data so I can modify the data and fix back the crc32 security after modification?


Comments

  • #2
    JimmyCrackCorn
    Registered Users, Registered Users 2 Posts: 1,691 ✭✭✭JimmyCrackCorn


    If you have enough samples you can work it out.
    Otherwise you have to calculate it and try and work it out yourself.
    Best to write it up in c and work it out that way using brute force.

    The crc is usually at the end but not always.

    Any help on this is situational dependently.

    Algorithm is here.
    http://en.wikipedia.org/wiki/Cyclic_redundancy_check


  • #3
    DublinDilbert
    Registered Users, Registered Users 2 Posts: 5,401 ✭✭✭DublinDilbert


    Are you sure it's a crc? It could also be a simple checksum or a hash of the data, using a hashing algorithm.

    As the poster above says if you have enough samples of data you might be able to brute force it...


  • #4
    Gavin
    Registered Users, Registered Users 2 Posts: 4,676 ✭✭✭Gavin


    RealistSpy wrote: »
    Hi,

    I hope this is the right place to post this but here is a scenario.

    I have a data but every time I modify the data in anyway the data gets corrupted. The data has a crc32 security.

    Is there anyways I can find out the crc32 offset in the data so I can modify the data and fix back the crc32 security after modification?

    Load the application which uses the data file into a debugger. Find the code which accesses the data and then just step through to see where the CRC is being calculated.


Advertisement