Shaun Mccran

My digital playground

23
J
A
N
2011

The Coldfusion Hash() function decoded - kind of

I've always believed that using the hash() function in ColdFusion is a one way process. If I wanted to reverse a string I had to use encode() and decode(). The Adobe documentation states that "It is not possible to convert the hash result back to the source string" - Adobe Docs for Hash().

Strictly speaking this is still true, but some bright spark has decided to host an MD5 string database and provide a lookup service.

The Hash() function has been around for a long time, in pre ColdFusion 7 versions of it you could not specify an algorithm, so you could only encode to MD5 standards.

In most cases the algorithm did not really matter too much. Most developers would have used hash() to store a password and perform real time character checks against the database values when a user submits a password string.

view plain print about
1Hash(string [, algorithm [, encoding ]])
2
3<cfset variables.encodedValue = hash('myPassword')>
4
5<cfoutput>#variables.encodedValue#</cfoutput>
6
7Results in:
8DEB1536F480475F7D593219AA1AFD74C

You could 'in-effect' never actually get a password back again, only perform a check against it using other hash()-ed strings.

The site http://www.md5decrypter.com/ appears to be hosting a database containing '8,076,999 unique MD5 hashes'. I've tested over a dozen random strings and they have all been successfully returned from their search.

It is probably more of a legacy application issue, but it is definitely worth noting that you really should specify an algorithm type when using the hash() function now.

This really makes a good case for revisiting those 'old' applications that never get a budget for bringing up-to-date.

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Justin Carter's Gravatar Technically you could do a lookup of any "one way" hash against a dictionary of hashes, regardless of the algorithm used (or seed). The main point definitely is to provide a *strong* seed to the hashing algorithm - someone could have a dictionary for lots of algorithm / seed combinations :P
# Posted By Justin Carter | 23/01/11 23:28
Shaun McCran's Gravatar @Justin, yes you could have a dictionary of hashed values for almost any algorithm,

Looking at the statistics though the more complex algorithms would need exponentially more records as they are many times more complex. This is even more evident if you compare the length of the same string encoded with MD5 and any one of the SHA algorithms.
# Posted By Shaun McCran | 23/01/11 23:39
Ron Stewart's Gravatar This is also why "salting" the string being hashed -- possibly with non-printable characters -- is also pretty important...
# Posted By Ron Stewart | 23/01/11 23:47
Jonah Chanticleer's Gravatar Glad to see I'm not the only person fixated on this topic. Great minds think alike, Shaun, eh? http://www.jonahchanticleer.com/post.cfm/md5-hashe... ;)

Joking aside, I wanted to thank you for the thought provoking tweet. It gave me incentive to do more writing than I have in a while.
# Posted By Jonah Chanticleer | 24/01/11 01:00
Shaun McCran's Gravatar @Jonah,

Glad I've re-ignited an interest :-)

@Ron, good point, any custom manipulation will greatly have an impact on the security of the data. Unless your manipulation device is unsecure, then you've just given the key to the vault away.
# Posted By Shaun McCran | 24/01/11 09:41
Peter Boughton's Gravatar The "correct" way to do password IS salted hashes.

Every user has a random salt calculated which is mixed with their password before hashing, ensuring that someone who gains access to the database cannot simply do a hash lookup to obtain a password.

Here's an article that starts with over-simple plain text passwords, then takes steps to explain why salt makes sense, and how to be most secure:
http://www.developerfusion.com/article/4679/you-wa...
# Posted By Peter Boughton | 24/01/11 10:12
John Whish's Gravatar MD5 is weak, you're much better off using one of the SHA algorithms. Jason Dean has an excellent security series on his blog http://www.12robots.com/
# Posted By John Whish | 24/01/11 14:03
Dominic Watson's Gravatar That hosted rainbow table lookup could be a great way to *test* your hashing methods (using salting, of course). You could even use it in a password strength tester! Api wrapper on Riaforge anyone?
# Posted By Dominic Watson | 24/01/11 19:51
Dominic Watson's Gravatar Oh, only just now visited the site and seen that it is not an api (publicly at any rate). Still, there must be something out there...
# Posted By Dominic Watson | 24/01/11 19:54
Shaun McCran's Gravatar @John, yes MD5 is undoubtedly the weakest of the algorithms in the hash() function. If you are using ColdFusion server 7+ I'd definitely use a stronger encryption method.

@Dominic, interesting idea. I wouldn't be surprised if it was possible to do that, or perhaps they even have an API they just haven't exposed.
# Posted By Shaun McCran | 24/01/11 21:32
Jonah C's Gravatar Made a discovery today while doing research for a project that made me feel a little foolish. Turns out US-CERT has specifically warned software developers, website owners, certificate authorities and end users to avoid MD5 (http://www.kb.cert.org/vuls/id/836068). SHA-2 seems to be the Federal Government agency standard for all new applications. Consider me officially schooled. :)
# Posted By Jonah C | 11/05/11 15:35
Shaun's Gravatar Thats an interesting article, thanks for the link :-)

Good to see there is an official GVMT standard.
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