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#1 Nckb  Icon User is offline

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How to do CRC calculation for Base64 string

Posted 01 August 2013 - 07:11 AM

Hi all,
I am trying to calculate a CRC of a Base64 string.
I know the answer of the checksum, but I don't how to calculate it (It is for Adobe project).

I give you the correct checksum : 2942042514
And now the string :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1aV67w3Q9MW/lL08UKSL+cuu8pc2yNoDGsRfkfYDqhPHOfRYtOtDGIVYwnxa
CXEujLaXyvamAMUop2PdFbzjv8g5pjHnC/HZWrI3pfkQH9MYMSckYQ8gI+DF
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Ur/yPYQL8jmXMjyZkU+Ne7MfKGNgCUfKM/xyUlQ2v9677VtInAItpE91DMS1
pWFd2UcM5/LEaF2abk653US53Sgt28Awq8XWz4YbKv9eABsuBZ+lwlPWoe5x
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xZozLyGn2YmPEk0p8rQzC7D1DHF+PUcZ1VewIjwD/ZSoNU5pZ+4xvJ/Dx8tw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apBnfchuzj5T3zrhmkDe6dQ7xeX7XDWJwRY7zvLXlrpVxYdqOrYy92vdxSAk
LTvjjZburcsMwVPEeXewt1Rciv0PAP8HNpcDbw==


I tried CRC 16, 32 and with polynomial 0xEDB88320L, and with all these tries, I cannot find the correct checksum, it is my main problem.

I don't want C++ code source, but I am searching for the method or algorithm to find it.
If you can help me, it will be helpful! And it is possible to have a gift for...

To know, it is for my own pleasure, not for a work or something else.

If you want to know, this string in base64 contains an string compressed in zip, which contains an UTF16 XML. I want to modify information, and modify Adobe Projet (prproj)

This post has been edited by modi123_1: 01 August 2013 - 07:15 AM
Reason for edit:: fixed the title, removed the word "challenge".


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Replies To: How to do CRC calculation for Base64 string

#2 modi123_1  Icon User is offline

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Re: How to do CRC calculation for Base64 string

Posted 01 August 2013 - 07:22 AM

Let me get this straight.. you have this string, which is a zip, which contains some XML for "Adobe Premier Pro", and you want to modify the bits of this string and still get a valid prproj afterward?
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#3 Nckb  Icon User is offline

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Re: How to do CRC calculation for Base64 string

Posted 01 August 2013 - 07:38 AM

View Postmodi123_1, on 01 August 2013 - 07:22 AM, said:

Let me get this straight.. you have this string, which is a zip, which contains some XML for "Adobe Premier Pro", and you want to modify the bits of this string and still get a valid prproj afterward?


Yes this is the job I am trying to do !
Prproj contains some mediaUID informations, and I want to modify my projects to change color or titles.
Today I am able to decode base64, uncompress string, modify the xml, and do a new compressed base 64 string.
But in prproj I have to indicate to correct checksum...
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#4 modi123_1  Icon User is offline

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Re: How to do CRC calculation for Base64 string

Posted 01 August 2013 - 07:48 AM

You want to just modify this string without disrupting the checksum?
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#5 Nckb  Icon User is offline

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Re: How to do CRC calculation for Base64 string

Posted 01 August 2013 - 08:14 AM

No, I want to modify string, and calculate the new Checksum ;)
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#6 modi123_1  Icon User is offline

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Re: How to do CRC calculation for Base64 string

Posted 01 August 2013 - 08:30 AM

Maybe I am a bit dense this morning, but so you get a new check sum and.. what?

You have an existing string and checksum.. you want to change the string and generate a new checksum?
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#7 Nckb  Icon User is offline

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Re: How to do CRC calculation for Base64 string

Posted 01 August 2013 - 08:43 AM

View Postmodi123_1, on 01 August 2013 - 08:30 AM, said:

Maybe I am a bit dense this morning, but so you get a new check sum and.. what?

You have an existing string and checksum.. you want to change the string and generate a new checksum?


Sorry, my english is so bad, I want to do exatly you said previously :)
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#8 modi123_1  Icon User is offline

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Re: How to do CRC calculation for Base64 string

Posted 01 August 2013 - 08:48 AM

Huh? What?

Okay so let's be clear - I want to know what the purpose of this is. Are you trying to bury changes in some file for less than legitimate reason, or what exactly?
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#9 Nckb  Icon User is offline

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Re: How to do CRC calculation for Base64 string

Posted 01 August 2013 - 12:04 PM

Exactly, I am trying to modify a lot subtitles of my personnal movies. If I don't do it with a progam it will take a lot of time...
Nothing illegal.
I have read some thread on Adobe community which talk about, but no real answers. No one of Adobe admin write about no legitime way. They just say there is no SDK to do it.

Thanks
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#10 Skydiver  Icon User is offline

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Re: How to do CRC calculation for Base64 string

Posted 01 August 2013 - 05:44 PM

What methods have you used to compute the checksum? You didn't go into any detail. I'm asking so that we don't waste our time going over ground that you've already covered.
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#11 Nckb  Icon User is offline

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Re: How to do CRC calculation for Base64 string

Posted 02 August 2013 - 04:41 PM

I used CRC 16 and 32 algorithm method as we can see on this link (I use other web sites for algorithms) http://damieng.com/b...32_in_C_and_NET
An other person says to me that it is probably calculate on base 64 string decoded, maybe it is a new way for me.
I am doing a method which searching checksum with a polynomial (incrementaly ++), I hope find it like this....

It is a real challenge for me this problem.

It will be a good things to find this checksum, a lot of people are talking about on Adobe forum, and there is no response... Admin says only : there is no SDK to calculate it, you have to do it by yourself! It will be a good thing for all !! ;)

I hope we will found how to calculate it !

Thanks by advance !

It is possible to give you all my source code, about base64 decoding, deflate zip string, converting utf16 to string, modify xml and reverse, and other method for CRC calculation. But I think, for you it is not the real problem...
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#12 martyata123  Icon User is offline

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Re: How to do CRC calculation for Base64 string

Posted 09 June 2014 - 09:21 AM

Hi there, did you manage to resolve your issue? I am having similar challenges and would love some guidance.
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#13 Nckb  Icon User is offline

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Re: How to do CRC calculation for Base64 string

Posted 09 June 2014 - 09:32 AM

View Postmartyata123, on 09 June 2014 - 09:21 AM, said:

Hi there, did you manage to resolve your issue? I am having similar challenges and would love some guidance.


Hi!
No, I haven't found, and I gave up, instead of looking for the CRC to put in the final XML file, I simply decodes the file to obtain the SRT file, and then I developed a program which is doing automatic actions to add changed subtitles in the project...
I do not have time to find the solution ...

If you find it, I'll be glad to see the solution, I broke my head on ;)
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