September 22, 2017 14:02 pm

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CRYPTO AND CODING

What is MD5 Hash and How to Use it

Md5

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In this post, I will discuss about one of the interesting cryptographic algorithm called MD5 in a very simple and easy to follow manner. In addition to understanding what is MD5 hash, you will also learn how to make use of this algorithm in your daily life.

What is MD5 algorithm?

MD5 which stands for Message Digest algorithm 5 is a widely used cryptographic hash function that was invented by Ronald Rivest in 1991. The idea behind this algorithm is to take up a random data (text or binary) as an input and generate a fixed size “hash value” as the output. The input data can be of any size or length, but the output “hash value” size is always fixed. Here is an example of MD5 Hash function at work:

MD5-Hash Function Example

As you can see from the above example, whatever the input size you give, the algorithm generates a fixed size (32 digit hex) MD5 hash. You can even try this on your own using the MD5 hash generator tool here.

Applications of MD5 Hash:

Before I tell you about how to use MD5, I would like to share one of my recent experience which made me start using MD5 algorithm.

Recently I made some significant changes and updates to my website and as obvious, I generated a complete backup of the site on my server. I downloaded this backup onto my PC and deleted the original one on the server. But after a few days something went wrong and I wanted to restore the backup that I downloaded. When I tried to restore the backup, I was shocked! The backup file that I used to restore was corrupted.

That means, the backup file that I downloaded onto my PC wasn’t exactly the one that was on my server. The reason is that there occurred some data loss during the download process. Yes, this data loss can happen often when a file is downloaded from the Internet. The file can be corrupted due to any of the following reasons:

  • Data loss during the download process, due to instability in the Internet connection/server.
  • The file can be tampered due to virus infections or
  • Due to Hacker attacks.

So, whenever you download any valuable data from the Internet, it is completely necessary that you check the integrity of the downloaded file. That is, you need to ensure that the downloaded file is exactly the same as that of the original one. In this scenario, the MD5 hash can become handy. All you have to do is generate MD5 hash (or MD5 check-sum) for the intended file on your server.

After you download the file onto your PC, again generate MD5 hash for the downloaded file. Compare these two hashes and if they match, that means the file is downloaded perfectly without any data loss.

A MD5 hash is nothing but a 32 digit hexadecimal number which can be something as follows:

e4d909c290d0fb1ca068ffaddf22cbd0

This hash is unique for every file irrespective of its size and type. For example, two different executable files (.exe files) with the same size will not have the same MD5 hash even though they are of same type and size. So MD5 hash can be used to uniquely identify a file. The same thing applies even for messages where each message that was sent and received can be verified using the MD5 hash.

How to use MD5 Hash to check the Integrity of Files?

Suppose you have a file called backup.tar on your server. Before you download, you need to generate MD5 hash for this file on your server. To do so use the following command:

For UNIX:

md5sum backup.tar

When you hit ENTER you’ll see something as follows:

e4d909c290d0fb1ca068ffaddf22cbd0

This is the MD5 hash for the file backup.tar. After you download this file onto your PC, you can cross check its integrity by again re-generating MD5 hash for the downloaded file. If both the hash matches then it means that the file is perfect. Otherwise it means that the file is corrupt. To generate the MD5 hash for the downloaded file on your Windows PC use the following freeware tool:

MD5 Summer

I hope you like this post. For further doubts and clarifications, please pass your comments. Cheers!

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Comments

  1. Hello…you Really Rock ! Can i ask u 1 q? do u know how to make a good template for a blog? please reply

  3. Is that “md5sum” inbuilt command ?
    Or have to install any extra packages?
    And another thing is that will it work on linux?

    • @ funcky

      MD5SUM is inbuilt on all UNIX systems. However on Windows your need to install the package. The download link is given in the post itself.

  11. Hi sri, i have one doubt , can we convert MD5 hash to a real string(text) , that should be the same used to convert MD5

    • @ Faizal

      MD5 hash is reversible only when you know the method and the key used for encryption. Often this is kept secret and hence it’s not possible to reverse it back in most cases. If you know then you can decrypt (reverse) it back.

  12. you rocks dude i have visited many hacking sites bt this is best awesome but i have problem in compiling file it tels so many errors

  14. Sir ur posts has been a guide and I love it so much.
    I too still ‘ve a problem on compiling file to exe? pls, where u said cd command has been my problem. I need ur help thanks.

  19. How can I use MD5 or SHA1 to to generate a hash value for an entire folder or even a jump drive.
    Phil

  23. it’s really incredible. You guys are making technology move to its limits.
    Am glad that your making things easier.
    Thanks………….

    Mr. faraaj sulaimam

  24. nice skills srikant i depreciate u, i just wanted to ask that how can we get the password of “[email protected]” in the form of md5 hash is it possible? i know how to crack that hashes just i dont know is how to get that hashes

  25. need help..

    I am sending a file from one server to remote server through sftp.

    they(remote server peoples) gave one MD5 Hash string to me.it contains 32 characters(alphanumeric).

    what can i do with this MD5 Hash string?

    how this MD5 hash string will be use in sending file?

    pls advice me

    Thanks in advance

  26. i loV u sir … u dnt knw i m really inspired by u …
    plzz tl me if ther is any good online couce on internet security or ethical hacking .. ?
    m waitin fr ur rpl … thnk u ….

  30. Hi Shrikant your posts are really amazing…bt I lik to know about Rainbow Hacking..pls make an article on Rainbow hacking…thnx in advnce…

  31. “This hash is unique for every file irrespective of it’s size and type. For example, two different executable files (.exe files) with the same size will not have the same MD5 hash even though they are of same type and size. So MD5 hash can be used to uniquely identify a file.”

    This is wrong.

    1) It’s impossible to iterate every possible file and have each one with a fixed length hash.
    Proof:
    File 1: Contents “1”: Hash #1
    File 2: Contents “2”: Hash #2
    etc
    File hashcombinations+1: No available hash

    2) MD5 is broken. It’s not collision resistant.

    • MD5 hash is reversible only when you know the method and the key used for encryption. Often this is kept secret and hence it’s not possible to reverse it back in most cases. If you know then you can decrypt (reverse) it back.

      Please tell me the procedure to reverse(decrypt)the text from md5 hash

  33. Am an engg student. am doing my project n cloud security. so i need to knw the data on cloud s secured using md5 passwrd encryption. reply soon sir.. i am waiting

  37. I know its very easy to break. So less secure but still its using in Many Applications

    -Krazyhack3r

  39. Best encryption for passwords and nobody can crack it until he have list of original password.

  43. wow it is an interesting keep it up!
    let me ask u one Q
    how can we compare two executable files or executable file with managed library in a C# project i hope u will help me.

  45. Also, want to add that it’s good to know the security issues around md5. I use it all the time and for that reason looked at security concerns with it. Mainly, it is possible for two different files to have identical hashes, but

    1) both files need to be created by the same person
    2) you cannot “target” a hash
    and
    3) hashes have finite combos so by dumb luck it is possible to have a “collision” … probability is very low

    Check this out for more info:
    http://geekswing.com/geek/the-magic-of-hash-and-i-mean-of-the-md5-and-sha-1-vintage/

  49. I downloaded a file from a site and calculated the MD5 value using two different applications and they were the same. But the value did not match the value given by the site. So I downloaded the file again and again six times and every time the value was different (conformed by both the applications) but matched the given value only the sixth time. Every time, the same file was downloaded from the same site and had the same size to the byte. Any explanations?

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