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Session tutorial: bring it back!

Posted: Wed Jun 23, 2004 5:38 pm
by tim
JASON - where did your 'introduction to session' tutorial go? It seems everyday I come across a oppurtunity to point someone to read that. And it would really REALLY help them dip their feet into sessions

I looked in the Wiki, no go

JASON, get your ass to work! :wink: :wink:

uh, please?

=]

Posted: Wed Jun 23, 2004 10:23 pm
by Illusionist
hehe, ya i noticed all Tutorials are gone except the header one. Where have they gone?!

Posted: Wed Jun 23, 2004 10:33 pm
by PrObLeM
Yea....Where all the white woman...i mean tutorials ...yea tutorials at!

Posted: Thu Jun 24, 2004 7:40 am
by tim
Illusionist wrote:hehe, ya i noticed all Tutorials are gone except the header one. Where have they gone?!
\most tuts went to the "Wiki" section

Problem your nasty lol :wink:

Posted: Thu Jun 24, 2004 11:02 am
by Illusionist
The "Wiki" confuses me!

Posted: Thu Jun 24, 2004 1:14 pm
by tim
i believe its one of those

"dont question just enjoy it" deals ill. lol

Posted: Thu Jun 24, 2004 3:31 pm
by Illusionist
:P i try!

Posted: Thu Jun 24, 2004 7:43 pm
by McGruff
Illusionist wrote:The "Wiki" confuses me!
What was it that was confusing?

Posted: Thu Jun 24, 2004 9:08 pm
by Weirdan
McGruff wrote:What was it that was confusing?
:roll: Everything ;) Wiki confuses me too... it's just... *looks at his nickname* weird! :D

Posted: Fri Aug 27, 2004 12:07 am
by Roja
I'll admit to not having visited in a while, but my md5 tutorial is gone from the tutorials section *and* isnt included in the Wiki.

Sup with that?

Posted: Fri Aug 27, 2004 2:50 am
by JayBird
I agree, that Wiki is the worst idea ever, so hard to find anything.

Bring back the tuts

Mark

Posted: Fri Aug 27, 2004 1:23 pm
by McGruff
Roja wrote:I'll admit to not having visited in a while, but my md5 tutorial is gone from the tutorials section *and* isnt included in the Wiki.

Sup with that?
We had a database problem a little while back and lost some data.

If you've still got a copy of the md5 tutorial, I'd be very grateful if you could send by PM.

Posted: Sat Aug 28, 2004 2:25 am
by Roja
McGruff wrote:
Roja wrote:I'll admit to not having visited in a while, but my md5 tutorial is gone from the tutorials section *and* isnt included in the Wiki.

Sup with that?
We had a database problem a little while back and lost some data.

If you've still got a copy of the md5 tutorial, I'd be very grateful if you could send by PM.
So wait, I spent an hour writing it, you post it to tutorials, people love it.

You then move it to a wiki, and lose it, and I need to find *my* backup copy?

Sadly, I would, but I dont have a backup copy.. I honestly thought it was 'safe' here.

Posted: Sat Aug 28, 2004 4:13 am
by patrikG
Roja wrote:Sadly, I would, but I dont have a backup copy.. I honestly thought it was 'safe' here.

Thank goat for Google's site-caching. They still have the text of it - albeit the formatting is lost:
Roja's md5 tutorial wrote:
(I would have posted this in the tutorials section, but only moderators can. I'm hoping this can be a single-thread source of md5 information - its a common topic).

What is MD5 or MD5sum?
Its a formula - a way to take a message of an arbitrary length, and create a 128-bit "fingerprint" or "message digest" of the message. MD5 is a way to verify data integrity. On these forums, it comes up fairly often in discussions about storing user passwords and other sensitive data.

Is MD5 encryption?
No. It is simply a one-way fingerprint of the message. It doesn't include the original message, and you can't (generally) use the fingerprint (the md5sum) to 'figure out' the original message.

Okay, so you take a message - like a password - and generate an MD5sum from it.. Can't you brute-force that?
Like any password system, you could attempt to brute force the answer. However, MD5sum's are in a 128-bit space, meaning that to brute force it would take 2^128 attempts - thats over 3 with 38 zeroes after it.

Neat! Thats a lot. Are there any flaws in the algorithm that could speed it up?
A birthday attack is based on the theory that there *might* be *one* md5sum that matches multiple inputs. In theory, it is possible that a "birthday" attack could be possible - two md5sum hashes could be the same. But even then, the total number of brute forces is at 2^64 attempts - still a heck of a lot.

Okay. But couldn't (insert super-sneaky government agency here) build an md5 dictionary, and know what the password was with the md5?
Yes. Its entirely possible. However - it would take some work to do so. For example, just for a dictionary consisting of Alphabet letters (upper and lower), and numbers, there would be 46,656,000,000 entries - all at 32 characters each. Thats over 1 terabyte of data to store and search! It could be done - absolutely. But is it likely?

So its hard to brute force, what about dictionary attacks?
Dictionary attacks are a way of attacking poor passwords - most people use words in their passwords. If you can guess the word - for example, "love", then you can cut down the number of tries it would take. Of course if you guess right, then your # of attacks = 1. However, in general, using common computers as of the writing of this (2003), you can generally get roughly 5 million attacks per second, or fast enough to guess all 8-character Alphanumericals within 497 days.

Thats pretty strong - but is there anything stronger?
A similar method is SHA1 - a more secure 160-bit hashing algorithm. That makes it *much* more secure against brute-force, birthday attacks, and other forms of assault. There are yet more hashing algorithms that are even stronger - but MD5 and SHA1 are both natively supported in the latest PHP, and should be sufficient for most projects.

Allright - I'm sold. Tell me how to use it to store passwords and check them
There are three things we are protecting against - the stored passwords, the transmission of the passwords, and the replay of the password. Each is very different. Lets start with the stored password. We need to take a password, and store it in a variable. Then we need to check that variable against what the user entered:

PHP:


$secret_password = md5("LOVE");
if (md5($_POST['password']) == $secret_password)
{
echo "Correct password";
}
else
{
echo "Incorrect password";
}




Simple enough. However, the password is being sent cleartext in $_POST['password']. Which brings us to another thing to protect against - the cleartext transmission. Thankfully, there is an opensource (GPL'd) javascript MD5 implementation available online. If you use that javascript library to md5 the password before sending it, the server code would look like this instead:

PHP:


$secret_password = md5("LOVE");
if ($_POST['password'] == $secret_password)
{
echo "Correct password";
}
else
{
echo "Incorrect password";
}




Again, fairly simple. However, I mentioned the other problem - replay attacks. If someone could manage to 'sniff' the connection, and capture the md5sum, they could simply use that to login!

The solution to that can be very complex and involved - the same site for the javascript md5 function goes into great detail discussing how to implement a truly secure solution. It's called a "CHAP" login system, and here is a link to his page on it - including complete working PHP and javascript code to implement it.

MD5 is a very useful means to protect user's passwords online - if used correctly. Its not encryption, but it does help prevent whole databases of passwords being compromised.

Good reading:

The PHP manual page for MD5 (http://us3.php.net/manual/en/function.md5.php)
The PHP manual page for SHA1 (similar, but stronger algorithm) (http://us3.php.net/manual/en/function.sha1.php)
RSA's explanation of MD2/4 and MD5 (http://www.rsasecurity.com/rsalabs/faq/3-6-6.html).

Posted: Sat Aug 28, 2004 9:57 am
by McGruff
Well done Patrik! I should have time to restore it over the weekend.

Roja: I do appreciate your effort. It was great to get a good quality tutorial.