How can I use bcrypt in a PHP application (and should I)?

Question

I am contributing to a relatively mature open source PHP project. I recently discovered that it stores passwords as simple MD5 hashes, which bothers me a lot. I thought that if I was going to fix this, I could also do it correctly (tm), so I wanted to use bcrypt.

First, what I found for other languages: bcrypt-ruby seems to use either the C source code from OpenBSD or the jBCrypt java code. py-bcrypt is a thin shell around BSD code. BCrypt.net is a direct port to jBCrypt .

Now PHP itself supports bcrypt (although it is mistakenly called simply "blowfish") in the crypt function . However, versions prior to 5.3 require support for the system itself, usually provided by crypt_blowfish . phpass is the same and recommends installing either PHP 5.3 or Suhosin .

Since many application users use standard shared hosting, I do not want to require any special server configuration. I was hoping to just steal the code from the PHP 5.3 release, but it is in C, and (from the small number of readings I just made), I cannot require the use of the C extension for project users.

I thought that I was just creating a bcrypt port with pure PHP, but looking at the source of jBCrypt I am not sure what should, given that I am not very familiar with PHP or blowfish, and the error here can be both dangerous and difficult to detect in the first place.

So, I present to you two (multi-part) questions:

• Is my lack of PHP knowledge getting better than me? Can I use one of the already created implementations?
• Should I instead just create a simple loooping function that calls sha1() or md5() several times for some custom number of times?

Answer 1

Is my lack of PHP knowledge getting better than me? Can I use one of the already created implementations?

Sorry, you're right. Prior to 5.3.0, PHP did not support bcrypt by default. Instead, he relied on OS support (check the CRYPT_BLOWFISH constant). As you indicated, Suhosin is an option in this case.

Should I instead just create a simple loooping function that calls sha1 () or md5 () several times for some custom number of times?

The best advice when it comes to cryptography is "don't collapse your own." Repeated calls to sha1() or md5() may or may not increase security.

The authors of bcrypt, on the other hand, explain their design decisions in this article .

Answer 2

Unfortunately, you cannot use bcrypt with Blowfish unless you are using PHP 5.3 or using the Suhosin extension, or perhaps the operating system supports Blowfish in its bcrypt implementation.

So, it’s best to use SHA-256 or SHA-512 with key streaming (and, of course, salt), but deploying your own solution is never a good idea when it comes to security.

Answer 3

One of the advantages of phpass that you didn't pay attention to was that it automatically reverts to using DES and finally MD5 as the base cipher if CRYPT_BLOWFISH is not available. The wrapper uses them in such a way that even an md5 implementation is much safer than a simple hash.