What is md5sum?
According to Wikipedia, md5sum is a program which calculates and verifies 128-bit MD5 hashes. The MD5 hash (or checksum) functions as a compact digital fingerprint of a file.
It is extremely unlikely for two non-identical files to have same md5sum as calculated by hashing algorithms (however the theory says something else).
What is the use of md5sum?
md5sum can be used as a general purpose file integrity verification. md5sum of any file will change if even a single bit of code is changed in the file. That means it can be used to verify the file. If any changes were made in that file, its md5sum will change for sure. This include changes from file transfer, disk error, medling etc. However a cryptanalytic attack on MD5 algorithm has been found which means a method has been to calculate a file that will have a given md5sum in less than time required for a bruting force attack (link old post here). So, MD5sum can’t be used where security is concerned but just where normal file integrity verification is required like protection against random bit flips.
How to calculate md5sum of a file?
In Unix, Linux, BSD variants (including MAC OS X) youdon’t need to install any third party application for checking md5sum, this facility is provided within the OS only. To know how to use it, follow this link on Wikipedia.
However Window users can’t do it without installing any third party application. If you are a Window user, give a try to MD5 Calculator which is a freeware and just 361 KB in size.
Download MD5 Calculator (Freeware – 361 KB)
Even I was aware of md5sum a few days back but then a little research did the job. Was you aware of it? Share your thoughts in the comment.
Thanks buddy! That helped me understand the facts about file duplication and transfer genuiness ! any ways could you help me in resolving CRC (Data error)