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How Do I Use MD5?


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#1 technickel

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Posted 18 November 2012 - 09:22 PM

Where do I find and how do I use MD5? I want to download and install some of the suggested anti-malware programs for running with McAfee, but don't want to install a malicious program unknowingly.
I've tried to use it before, but got a tad confused.

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#2 Andrew

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Posted 18 November 2012 - 10:42 PM

There are a number of tools for finding the MD5 hash for a given file. I use and recommend HashTab.

#3 Didier Stevens

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Posted 19 November 2012 - 08:09 AM

You are asking how to obtain and verify a cryptographic hash (md5, sha1, ...) for a program you download.

It is up to the publisher of the program to decide if they want to publish a cryptographic hash or not. If they do, most of the time they are on the download page. You download the program and you take notice of the hash (for example md5). When the program is downloaded, you calculated the hash of the program on your machine with tools like Andrew mentioned. The hash you calculated should be identical to the hash published. If they are different, you know that the program you downloaded is not the same as the program for which the hash was published.

A simpler way to achieve the same result is to verify the digital signature of the program you downloaded. Take the properties of the file and select the tab Digital Signatures. If this tab is missing, the program is not signed.
If the tab is present, click Details and see if the signature is valid or not.

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#4 technickel

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Posted 19 November 2012 - 09:53 AM

Didier, when you say, "take the properties of the file and select the tab, 'digital signatures'", do you mean rt. click on the downloaded file, and select properties?

#5 Didier Stevens

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Posted 19 November 2012 - 09:59 AM

Didier, when you say, "take the properties of the file and select the tab, 'digital signatures'", do you mean rt. click on the downloaded file, and select properties?


Correct.

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#6 technickel

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Posted 19 November 2012 - 03:27 PM

Didier, how do I know if the signature is valid after clicking on details?

#7 Didier Stevens

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Posted 19 November 2012 - 03:48 PM

Didier, how do I know if the signature is valid after clicking on details?


By reading what is displayed in the dialog box: "This digital signature is OK." or another message that tells you why the signature is not OK.

Didier Stevens
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http://DidierStevensLabs.com

SANS ISC Senior Handler
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If you send me messages, per Bleeping Computer's Forum policy, I will not engage in a conversation, but try to answer your question in the relevant forum post. If you don't want this, don't send me messages.

 

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