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Difference between md5 and iso. Ask Question -3. What exactly is the difference between an md5 and an iso. Disadvantages and advantages of both? When you download disk images like iso there is *.md5 included! The md5 is a hash of the related iso in order to verify its integrity! Check ISO for errors without MD5 and how to find MD5 for. From Manjaro Linux. How to check an.iso file with an MD5 hash. If your system doesn't have md5sum (used in the example here) or another MD5 hash checking tool, then you will need to install one. There are a number in the AUR that you will find by searching for md5sum. If they don't match you need to download the.iso again.
Last month, Linux Mint’s website was hacked, and a modified ISO was put up for download that included a backdoor. While the problem was fixed quickly, it demonstrates the importance of checking Linux ISO files you download before running and installing them. Here’s how.
Linux distributions publish checksums so you can confirm the files you download are what they claim to be, and these are often signed so you can verify the checksums themselves haven’t been tampered with. This is particularly useful if you download an ISO from somewhere other than the main site–like a third-party mirror, or through BItTorrent, where it’s much easier for people to tamper with files.
How This Process Works
The process of checking an ISO is a bit complex, so before we get into the exact steps, let’s explain exactly what the process entails:
- You’ll download the Linux ISO file from the Linux distribution’s website–or somewhere else–as usual.
- You’ll download a checksum and its digital signature from the Linux distribution’s website. These may be two separate TXT files, or you may get a single TXT file containing both pieces of data.
- You’ll get a public PGP key belonging to the Linux distribution. You may get this from the Linux distribution’s website or a separate key server managed by the same people, depending on your Linux distribution.
- You’ll use the PGP key to verify that the checksum’s digital signature was created by the same person who made the key–in this case, the maintainers of that Linux distribution. This confirms the checksum itself hasn’t been tampered with.
- You’ll generate the checksum of your downloaded ISO file, and verify it matches the checksum TXT file you downloaded. This confirms the ISO file hasn’t been tampered with or corrupted.
The process may differ a bit for different ISOs, but it usually follows that general pattern. For example, there are several different types of checksums. Traditionally, MD5 sums have been the most popular. However, SHA-256 sums are now more frequently used by modern Linux distributions, as SHA-256 is more resistant to theoretical attacks. We’ll primarily discuss SHA-256 sums here, although a similar process will work for MD5 sums. Some Linux distros may also provide SHA-1 sums, although these are even less common.
Similarly, some distros don’t sign their checksums with PGP. You’ll only need to perform steps 1, 2, and 5, but the process is much more vulnerable. After all, if the attacker can replace the ISO file for download they can also replace the checksum.
Using PGP is much more secure, but not foolproof. The attacker could still replace that public key with their own, they could still trick you into thinking the ISO is legit. However, if the public key is hosted on a different server–as is the case with Linux Mint–this becomes far less likely (since they’d have to hack two servers instead of just one). But if the public key is stored on the same server as the ISO and checksum, as is the case with some distros, then it doesn’t offer as much security.
Still, if you’re attempting to verify the PGP signature on a checksum file and then validating your download with that checksum, that’s all you can reasonably do as an end-user downloading a Linux ISO. You’re still much more secure than the people who don’t bother.
How to Verify a Checksum On Linux
We’ll use Linux Mint as an example here, but you may need to search your Linux distribution’s website to find the verification options it offers. For Linux Mint, two files are provided along with the ISO download on its download mirrors. Download the ISO, and then download the “sha256sum.txt” and “sha256sum.txt.gpg” files to your computer. Right-click the files and select “Save Link As” to download them.
On your Linux desktop, open a terminal window and download the PGP key. In this case, Linux Mint’s PGP key is hosted on Ubuntu’s key server, and we must run the following command to get it.
Your Linux distro’s website will point you towards the key you need.
We now have everything we need: The ISO, the checksum file, the checksum’s digital signature file, and the PGP key. So next, change to the folder they were downloaded to…
…and run the following command to check the signature of the checksum file:
If the GPG command lets you know that the downloaded sha256sum.txt file has a “good signature”, you can continue. In the fourth line of the screenshot below, GPG informs us that this is a “good signature” that claims to be associated with Clement Lefebvre, Linux Mint’s creator.
Don’t worry that the key isn’t certified with a “trusted signature.” This is because of the way PGP encryption works–you haven’t set up a web of trust by importing keys from trusted people. This error will be very common.
Lastly, now that we know the checksum was created by the Linux Mint maintainers, run the following command to generate a checksum from the downloaded .iso file and compare it to the checksum TXT file you downloaded:
You’ll see a lot of “no such file or directory” messages if you only downloaded a single ISO file, but you should see an “OK” message for the file you downloaded if it matches the checksum.
You can also run the checksum commands directly on an .iso file. It’ll examine the .iso file and spit out its checksum. You can then just check it matches the valid checksum by looking at both with your eyes.
For example, to get the SHA-256 sum of an ISO file:
Or, if you have an md5sum value and need to get the md5sum of a file:
Compare the result with the checksum TXT file to see if they match.
How to Verify a Checksum On Windows
If you’re downloading a Linux ISO from a Windows machine, you can also verify the checksum there–though Windows doesn’t have the necessary software built-in. So, you’ll need to download and install the open-source Gpg4win tool.
Locate your Linux distro’s signing key file and checksum files. We’ll use Fedora as an example here. Fedora’s website provides checksum downloads and tells us we can download the Fedora signing key from https://getfedora.org/static/fedora.gpg.
After you have downloaded these files, you’ll need to install the signing key using the Kleopatra program included with Gpg4win. Launch Kleopatra, and click File > Import Certificates. Select the .gpg file you downloaded.
You can now check if the downloaded checksum file was signed with one of the key files you imported. To do so, click File > Decrypt/Verify Files. Select the downloaded checksum file. Uncheck the “Input file is a detached signature” option and click “Decrypt/Verify.”
You’re sure to see an error message if you do it in this way, as you haven’t gone through the trouble of confirming those Fedora certificates are actually legitimate. That’s a more difficult task. This is the way PGP is designed to work–you meet and exchange keys in person, for example, and piece together a web of trust. Most people don’t use it in this way.
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However, you can view more details and confirm that the checksum file was signed with one of the keys you imported. This is much better than just trusting a downloaded ISO file without checking, anyway.
You should now be able to select File > Verify Checksum Files and confirm the information in the checksum file matches the downloaded .iso file. However, this didn’t work for us–maybe it’s just the way Fedora’s checksum file is laid out. When we tried this with Linux Mint’s sha256sum.txt file, it did work.
If this doesn’t work for your Linux distribution of choice, here’s a workaround. First, click Settings > Configure Kleopatra. Select “Crypto Operations,” select “File Operations,” and set Kleopatra to use the “sha256sum” checksum program, as that’s what this particular checksum was generated with. If you have an MD5 checksum, select “md5sum” in the list here.
Now, click File > Create Checksum Files and select your downloaded ISO file. Kleopatra will generate a checksum from the downloaded .iso file and save it to a new file.
You can open both of these files–the downloaded checksum file and the one you just generated–in a text editor like Notepad. Confirm the checksum is identical in both with your own eyes. If it’s identical, you’ve confirmed your downloaded ISO file hasn’t been tampered with.
These verification methods weren’t originally intended for protecting against malware. They were designed to confirm that your ISO file downloaded correctly and wasn’t corrupted during the download, so you could burn and use it without worrying. They’re not a completely foolproof solution, as you do have to trust the PGP key you download. However, this still provides much more assurance than just using an ISO file without checking it at all.
Image Credit: Eduardo Quagliato on Flickr
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Contents
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When one has downloaded an ISO file for installing or trying Ubuntu, it is recommended to test that the file is correct and safe to use. The MD5 calculation gives a checksum (called a hash value), which must equal the MD5 value of a correct ISO.
The program md5sum is designed to verify data integrity using the MD5 (Message-Digest algorithm 5) 128-bit cryptographic hash. MD5 hashes used properly can confirm both file integrity and authenticity.
In terms of integrity, an MD5 hash comparison detects changes in files that would cause errors. The possibility of changes (errors) is proportional to the size of the file; the possibility of errors increase as the file becomes larger. It is a very good idea to run an MD5 hash comparison check when you have a file like an operating system install CD that has to be 100% correct.
In terms of security, cryptographic hashes such as MD5 allow for authentication of data obtained from insecure mirrors. The MD5 hash must be signed or come from a secure source (an HTTPS page) of an organization you trust. See the MD5SUMS file for the release you're using under http://releases.ubuntu.com (and optionally the PGP signatures in the MD5SUMS.gpg file), or refer to the secure UbuntuHashes page for the official list of Ubuntu MD5 hashes.
While security flaws in the MD5 algorithm have been uncovered, MD5 hashes are still useful when you trust the organization that produces them. Moving to more secure hashes like SHA-256 and Whirlpool is under discussion.
The official page containing MD5 hashes for Ubuntu, Kubuntu, Edubuntu Xubuntu and Lubuntu is UbuntuHashes. More recent hashes may be available at http://releases.ubuntu.com/ : choose the relevant distribution and click on the MD5SUMS file.
Most Linux distributions come with the md5sum utility so installation is usually unnecessary.
Check the iso file
Manual method
First open a terminal and go to the correct directory to check a downloaded iso file:
- Linux is case sensitive so 'Downloads' is NOT 'downloads'.
Then run the following command from within the download directory.
md5sum should then print out a single line after calculating the hash:
Compare the hash (the alphanumeric string on left) that your machine calculated with the corresponding hash on the UbuntuHashes page.
An easy way to do this is to open the UbuntuHashes page in your browser, then copy the hash your machine calculated from the terminal into the 'Find' box in your browser (in Firefox you can open the 'Find' box by pressing <Ctrl> <F>).
When both hashes match exactly then the downloaded file is almost certainly intact. If the hashes do not match, then there was a problem with either the download or a problem with the server. You should download the file again from either the same mirror, or from a different mirror if you suspect a server error. If you continuously receive an erroneous file from a server, please be kind and notify the webmaster of that mirror so they can investigate the issue.
Semi-automatic method
Ubuntu distributes the MD5 hashes in a file called MD5SUMS near the bottom of the download page for your release http://releases.ubuntu.com.
First download the MD5SUMS file to the same directory as the iso. Then run the following in a terminal.
md5sum will generate a bunch of warnings. Don't worry: the OK message will be buried somewhere within it!
In this case the message we want is on the seventh line.
Success?
Once you have verified the md5 hash, go ahead and burn the CD. You may want to refer to the BurningIsoHowto page.
Check the CD
So far so good, you have downloaded an iso and verified its integrity. When you boot from the CD you will be given the option to test its integrity. Great, but if the CD is corrupt then you have already wasted time rebooting. You can check the integrity of the CD without rebooting as follows.
Checking the CD directly
You would think you could simply use a command like this to get the MD5 hash of a burned image:
However this will almost NEVER be the same hash as the iso image that was burned to the disk, because this command includes the empty space at the end of the disk, which changes the hash. So you must check only the part of the disk that was on the iso.
Manual method
First we need to know the size of the iso image. You could open up your favorite graphical file manager such as Nautilus or Dolphin, but since you need to use the command line anyways, you might as well use ls.
Now that we know the size of our iso image is 732766208, we can use dd to pipe only 732766208 bytes from our cdrom device into md5sum. Use a block size of 1 and set count to the size of the iso image. Note that this will probably take several minutes, so grab a snack and come back in a while.
You could probably speed this up by using a larger block size (bs) and dividing count by the new block size. Since all iso images are multiples of 2048, that is an appropriate block size.
Check the calculated hash (in this case 24ea1163ea6c9f5dae77de8c49ee7c03) against UbuntuHashes as shown for the iso file above. Depending on your system, you may need to change cdrom to cdrom0 (or even cdrom1 if you have two CD drives).
Automated Script
Here is a shell script that will check the md5 hash of a burned disk and compare it to the hash of an iso image. Copy and paste it into your favorite text editor and save it as eg. hashcdrom.sh.
Now open a terminal and type
Note that if your cdrom device is /dev/cdrom, you can omit that parameter.
It should print out something like
If you verified that the iso image is okay (above), than you need not check the hash against UbuntuHashes.
This script has some nifty features. For example, if md5deep is installed (sudo aptitude install md5deep), it will use it to print out some progress information, such as how many bytes copied. You can also make it use different hashing algorithms such as sha256 and whirlpool by setting the CHECKSUM environment variable to the command you want to use to create the hash:
![How to check md5 of linux iso download mac How to check md5 of linux iso download mac](https://www.alloappforpc.com/wp-content/uploads/2015/08/MD5-Check-Utility2B.jpg)
This shell script depends on certain features found only in GNU grep, so it probably will not work on systems that do not ship the GNU utilities.
A method using wodim instead of dd
where 352113 is result of dividing size of iso file in bytes by 2048.
Check the files on the CD
The MD5 hashes for every file on the CD are listed in a file called md5sum.txt. You can use this file to check the integrity of all the files on the CD.
This will automatically check every file against the MD5 hashes stored in the file and outputs any failures. (Again, you may need to change cdrom, depending on your system). Beware, it can take a long time so don't worry if your terminal seems to have hung; provided the CD drive is still accessing, it is probably still working. It should not output anything if it there were no errors, and an error message if a file failed the check. The grep command option -v 'OK$' filters out all of the files that pass the check, because there are usually a lot of them.
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Success?
Congratulations, you now have a verified Ubuntu CD. Go ahead and use it (or play frisbee with it if you want).
There are three methods of using md5sum on an OS X machine.
Method 1 - The easiest (if MD5 is available) is using the Disk Utility program (Applications > Utilities, or by choosing 'Utilities' from the Finder's 'Go' menu). Open Disk Utility and wait for it to gather information about your disks. Go to the directory where you downloaded the Ubuntu disk image, and drag it to Disk Utility's dock icon (displays on the left-hand side of Disk Utility, underneath your physical drives). Select the iso file. Go to the 'Images' menu and select Checksum > MD5. Be sure to choose 'MD5' and NOT 'MD5 image checksum' or 'CRC-32 image checksum', as they are not the same and will give you different results.
Method 2 - If MD5 is not available in the Images > Checksum menu, open a terminal window (Applications > Utilities > Terminal.app). Type 'md5', type a space, drag the iso file into the terminal window (appends command with iso file path), and press Enter. The command line returns the hash number.
Method 3 - You can use the Terminal.app and follow the instructions for MD5SUM on Linux, except use the command 'openssl md5' instead of 'md5sum'.
Each method returns a hash number. Compare the hash number with the corresponding hash on the UbuntuHashes page. When both hashes match exactly, then the downloaded file is almost certainly intact.
If the hashes do not match, then there was a problem with either the download or a problem with the server. You should download the file again from either the same mirror, or from a different mirror if you suspect a server error. If you continuously receive an erroneous file from a server, please notify the webmaster of that mirror so they can investigate the issue.
Use the Solaris digest(1) command, specifying the md5 algorithm with the -a flag. For instance:
Windows does not come with md5sum. You must download one from another location, preferably one that you trust. There are command line utilities (md5sum.exe) that work similarly to the Unix utility; one public domain version with source is available from Fourmilab, but the version available from Cygwin is probably easier to install and update, and Cygwin is also recommended and trusted as the source for many more Unixy utilities. Once installed, Cygwin's md5sum behaves exactly as described in MD5SUM on Linux above.
There are also graphical tools such as the one used in the walk-through provided below.
- Download and install winMD5Sum, a free and open source hash verification program.
- Right-click the ISO file.
- Click Send To, then winMD5Sum.
- Wait for winMD5Sum to load and finish the checksum (this may take a significant amount of time depending on your computer's performance).
- Copy the corresponding hash from UbuntuHashes into the bottom text box.
- Click 'Compare'
- A message box will say 'MD5 Check Sums are the same' if the hashes are equal.
'Checksums calculator” is a free file checksum calculation utility, it can support the most commonly used file checksum algorithm, such as md5, crc32, and sha1, can batch process multiple files. This verification software has some useful features, but it is easy to understand and very easy to use. You can download the application here.
The program while is running under Windows 7 64bit.
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To see if your Ubuntu CD was corrupted when burned to the disk, see the CDIntegrityCheck page, or follow the instructions below.
First mount the CD, if not already mounted:
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Then use the supplied md5sum file on the CD:
Be patient, it takes some time. If the command outputs any errors, you'll know that either the burn was bad or the .iso is corrupt. Please note that this method does not verify authenticity unless the hash of the iso file is compared to the hash at the secure UbuntuHashes page.
Finally, you can unmount the CD after leaving the folder:
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