MD5 Algorithms in web development

Question

I am storing the passwords of my college website in our own server. I am storing the passwords using the MD5 encryptor. But the doubt I got is since the decrypter is there I can also decrypt the passwords and use them. So how these passwords are secured with me.

Answer 1

MD5 is not an encryption algorithm. It is a hash algorithm. Hash algorithm are one-way. There is no decryptor.

Hashes are used to generate a fingerprint of a text string. Reverse-engineering the input from the hash should be impossible. When the hash-function is cryptographically secure, there should be no way which is more efficient than trying out all possible inputs until you find one which coincidally has the same hash.

How do you apply this in a password system?

When the user tells you their password during registration, you don't save it. You generate the hash of the password, save the hash in the database, and forget that you ever saw the cleartext password. When a user then tries to login, they give you a password. You generate the hash of that password, and when it matches the hash in your database, you let them in.

But please note that MD5 is no longer a good choice for password encryption.

1. MD5 is a fast algorithm. At first glance this seems like an advantage because it makes authentication faster. But it also makes it much easier for anyone with access to the hash to try out passwords until they found one which matches.
2. The security of MD5 is disputed. Many flaws were discovered in the algorithm which make it possible to reverse-engineer the input of an MD5 hash in some scenarios.

For these reasons, you should use another algorithm when possible. A good choice for password encryption is bcrypt, because it was designed especially for this purpose. When an implementation is not readily available for your development framework, SHA-2 can be considered an alternative where implementations are easier to come by. It's not considerably slower than MD5 which makes it easier to crack given enough computing-power, but it has no known critically vulnerabilities like MD5. For low-security systems it's still adequate.