Let's say you work at a bank, and your job is to enter a list of account numbers, together with some data about each account, into the computer system. How do you know that at the end of a long session of entering data, you have typed in everything accurately? This is especially so for things like account numbers, which have no inherent meaning unlike normal words , and therefore are easy to get wrong.
One possible way is to use a checksum. Let's say that the account numbers use the format of "", where the last digit is a checksum. If you make a mistake and enter "" instead where the third digit should be 3 instead of 4 , the computer system instantly knows that you have made a mistake somewhere, since an account number beginning with the digits "" should have a final digit, the checksum, of "6", but you entered "5".
Notice though that it is still possible to have an account number that is entered wrongly, but where the checksum is unable to show that error, since, in this example, we only have 10 possible checksums, 0 to 9, for the 1 billion possible account numbers.
They are usually meant only to be a quick and dirty way of detecting certain errors. That said, the algorithm used in this example, where we only preserve the last digit of the sum, is particularly flawed. Hashes are similar to checksums, except that they were originally created for other purposes besides error checking.
However, by design, hashes are often unique for a wide range of data though not all possible data , unlike my lousy checksum method mentioned in the above example, so they are sometimes used as a quick and dirty way to check if the file we downloaded is most likely the same one that the author or distributor intended us to have. When you check a file you downloaded to see if it is genuine, that is, that it has not been tampered with nor has it been corrupted in transit, you should note the following:.
The file sizes must also be identical. An identical checksum or hash alone is not enough. That is, even if a particular hash algorithm ie, method allows 2 different files of the same size to end up with the same sequence of letters and numbers, it is less likely that those files also produce matching hashes for all the other algorithms. Or to put it simply in case the above paragraph has too much technobabble, making it difficult to understand , if a website provides many types of hashes for a file, and you can match them all with the file you downloaded, and it has the same size as the original, you have greater assurance that you have the same file as that listed on the website.
The commonly provided hashes have their own problems, in that they are known to have collisions, where different files can actually end up with the same hash. That is why I said earlier that you have greater confidence if all the hashes match, since it is probably harder to create a tampered file that provides matching hashes for every single algorithm. For all this checking to have any use at all, the site from which you get the hashes must be reliable and trustworthy.
In addition, your connection to it must be secure. Otherwise you may be checking against hashes that have also been tampered with, giving you false confidence that your file is legitimate. This increases the risk even more, since there is a chance that you are not really connected to the website you think you are accessing. Someone on the Internet or on your WiFi connection or network can substitute a fake website that seems to be at the correct address, but provide hashes for a tampered file.
It does not mean that it is not infected with malware. Remember that anyone's computers can get infected, even the people from whom you are getting the file, resulting in the files they distribute being infected.
The hashes provided may have been generated unknowingly or even knowingly after those files were infected. This allows you to find the hash value with just two clicks. We can add all these algorithms as sub-options to the Hash option in the right-click menu.
Though sounds complicated, it is very easy to do. Just follow the steps as is and it will be done in no time. Since we need to create a lot of new values for different types of hash algorithms, to make things easier, I made the reg file for you. Download the file from here and extract the contents of the zip file to your desktop.
You will see a prompt asking if you like to merge the file with your Registry. Once merged, you will see a prompt telling you the same. However, calculating the hash of the same file string twice will result in the same output. Hash calculated with different algorithms will obviously give different result.
They are used to verify the integrity of files used for this also in computer forensics. Well, once downloaded on your PC, to verify that the file is intact free of transmission errors or voluntary tampering due to MITM attacks you just need to recalculate the hash locally and compare it with the string provided online. You can use CertUtil :.
It is not possible to generate CRC32, however, for Windows there is also a very useful free program from Nirsoft ,.
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