You want salt with that?

Yes you would, and you should!

Explanation follows shortly. Over the last few weeks, I’ve been helping out a friend with his new site. He payed some programmers from India a few hundred euros to complete the site, and they did.

However, they made more than a few errors!

The first most n00bish error they made, was not to properly escape input to MySQL, meaning the whole site was vulnerable to SQL injection attack. I tried it, and it worked like a charm = bad!

This error was quick to fix, and zoon after the site was a tad bit more secure. But then I discovered the next big(huge!) mistake.

All passwords are stored in PLAINTEXT in the database!!!!1!!

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Why is this bad? Well, if someone got a hold of the database, they could use it to access that persons account. They could even be so lucky, that they could access a different site, using the same username and password = not good!

People are generally not good at using different passwords for different sites.

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So what are the options?

• Store the cryptographic hash (aka message digest) of the password instead of the password.
• Store the cryptographic hash of the message + a salt

If you just want security against you plain kiddy hacker, you could go for option number one.
[sourcecode language=”php”]
<?php
mysql_query( sprintf("insert into usertable(name,password) values (‘%s’,’%s’)", mysql_real_escape_string($username), mysql_real_escape_string( md5($password)));
?>
[/sourcecode]

However, MD5 has been proven to be “weak”. You could/should replace it with SHA256.

If a good(proven) hacker gets hold of your passwords in the database, he would most likely use a Rainbow table to reverse engineer all the passwords.

Using a salt
Lets say that you for each user in your usertable, adds a new field which contains a salt. This salt is different for each user. The length of the salt should be fairly high, say about >128 characters.

Before the password is hashed, the password is appended/prefixed the random generated hash value.
[sourcecode language=”php”]
<?php
// generated random salt – length 128 chars
$salt = substr(md5(uniqid(rand(), true)), 0, 128);
// generate hash with salt
$hash = md5($salt.$password);
?>
[/sourcecode]

If the attacker gets hold of your usertable, he (or she for that matter) will have to calculate a new Rainbow table for each user. The larger the salt you use, the bigger the Rainbow table, the longer it takes to calculate.

A hidden salt value would be ideal, but thats not always possible.