PHP - MD5, SHA, Hashing security

Question

I'm the developer of a new website built in PHP and I'm wondering what exactly is the best thing to use for hashing. I've looked at md5 and sha1 but is there anything more secure.
I'm sorry if this is a nooby question but I'm new to PHP Security and I'm trying to make my site as secure as possible. Also what is a salt?
Thanks,
Waseem

Answer 1

First off md5 and sha1 have been proven to be vunrable to collision attacks and can be rainbow tabled easily (When they see if you hash is the same in their database of common passwords).
There are currently two things that are secure enough for passwords, that you can use.
The first being sha512. sha512 is a sub-version of SHA2. SHA2 has not yet been proven to be vunrable to collision attacks and sha512 will generate a 512 bit hash. Here is an example of how to use sha512:

<?php
hash('sha512',$password);

The other option is called bcrypt. bcrypt is famous for its secure hashes. Its probably the most secure one out there and most customizable one too.
Before you want to start using bcrypt you need to check if your sever has it enabled, Enter this code:

<?php
if (defined("CRYPT_BLOWFISH") && CRYPT_BLOWFISH) {
    echo "CRYPT_BLOWFISH is enabled!";
}else {
echo "CRYPT_BLOWFISH is not available";
}

If it returns that it is enabled then the next step is easy, All you need to do to bcrypt a password is (Note for more customizability you need to see this How do you use bcrypt for hashing passwords in PHP?):

crypt($password, $salt);

Now to answer your second question. A salt is usally a random string that you add at the end of all you passwords when you hash them. Using a salt means if some one gets your database they can not check the hashes for common passwords. Checking the database is called using a rainbow table. You should always use a salt when hashing!!

Here are my proofs for the SHA1 and MD5 collision attack vulnerabilities:
http://www.schneier.com/blog/archives/2012/10/when_will_we_se.html, http://eprint.iacr.org/2010/413.pdf, http://people.csail.mit.edu/yiqun/SHA1AttackProceedingVersion.pdf, http://conf.isi.qut.edu.au/auscert/proceedings/2006/gauravaram06collision.pdf and Understanding sha-1 collision weakness

Answer 2

The whole purpose of the salt is to slow down an attacker from comparing a list of pre-generated hashes against the target hash.

Instead of needing to pre-compute one "hashed" value for each plaintext password, an attacker needs to precompute 16384 "hashed" values for each plaintext password (2^7 * 2^7).

That kinda pales today but was pretty big when the crypt function was first developed - the computational power to pre-compute that many passwords times the number of plaintext password you suspect (dictionary) was pretty high.

Not so much today which is why we have things like shadow passwords, other core password functions besides crypt and every sysad wanting you to pick a password that would not show up in a dictionary.

If the hashes you want to generate are for passwords this is a well accepted method of implementing it.

http://www.openwall.com/phpass/