How to verify data integrity using MD5 cryptographic algorithm

What is MD5 you ask? 

MD5 stands for message digest 5. It's an algorithm used to create data digest to verify it's integrity. Just like every human being has unique fingerprint, every file that goes through this algorithm brings a fixed length hash, this hash cannot be reversed.

What's the use of MD5?

MD5 is most commonly used to hash user password and data verification. When user signs up to a website his password is hashed, and stored in the database, when user tries to login, his password is again hashed and matched against the hash stored in database. So even if his website database is compromised, hacker wouldn't be able to see the passwords, thought this doesn't mean your data is completely secure, more often than not users use common passwords like 123456, 00000 etc.. hacker would simple use a dictinary of common known hashes to crack down your password, so it's very important that your suggest user to choose as strong password as possible.

How does data verification work with MD5?

Data verification or data integrity check work by creating a digest or hash of a certain application/file, every digest generated by MD5 is unique. For example, lets say you've made a file avilable for download, how would the users know whether someone who's linking to a mirrored download is a genuine file and not some virus attached to original file? Well that's where MD5 comes into play, you can compute an hash of your application and post it on your website, now whenever someone downloads it from your or someone else's website he would use a utility like Microsoft file checksum integrity verifier to compute a hash for either MD5 or SHA1, and compare it against the hash that was provided on your original website, if the hash is same, the file's exact as the original one, else, something in that file has been modified.