MD5 Checksum for Images (Binaries) in CF
Note: If you want to skip my ramble and get to the solution scroll to the bottom for the example code and download.
I thought it would be nice and easy to do it with the CF Hash function and on first attempt it appeared to be:
Hash: <cfoutput>#hash(myTextFile)#</cfoutput>
However, the hashes get created on by CF but get verified by an Flex application so I was using the as3corelib's MD5 function and couldn't get the hashes to match.
So I decided to try another MD5 implementation to see which of my functions was wrong - unfortunately it turned out that both of them were wrong but for two different reasons. I'll cover the AS3 problem in a different post.
The output from md5sum was as follows:
2346b6ab017de31688ee35949612db07 firework.jpg
This didn't match what I had generated. A bit more head scratching and I realised that the problem was that I was trying to do an md5 hash on a binary file but the CF Hash() only takes a "string".
After loading the file with "readbinary" the hash function didn't work (no surprise) and a bit of digging around led me to use some Java functionality to handle the generation of the Hash.
<cfset var md5 = createObject("java","java.security.MessageDigest").getInstance("MD5")>
<cfset md5.update(myBinaryFile,0,len(myBinaryFile))>
<cfset checksumByteArray = md5.digest()>
This leaves us with a ByteArray digest of the file - which we need to convert to a familiar hex encoded MD5 Hash.
<cfset hexCouplet = formatBaseN(bitAND(checksumByteArray[i],255),16)>
<!--- Pad with 0's --->
<cfif len(hexCouplet) EQ 1>
<cfset hexCouplet = "0#hexCouplet#">
</cfif>
<cfset checkSumHex = "#checkSumHex##hexCouplet#">
</cfloop>
Binary Hash: <cfoutput>#checkSumHex#</cfoutput>
Bingo - all working nicely now. I've packaged it all up to make my life easier I've packaged it up into a nice CFC - Crypto.cfc.
Solution and Download
Here's the example code and a running demo of it.
The Crypto CFC is available from the subversion repository.
Here is the code to use it:
<cfset md5 = createObject("component","au.com.lynchconsulting.cfc.utility.Crypto").hashBinary(myBinaryFile)>
<h3>MD5 Sum calculated from hashBinary()</h3>
Hash Binary: <cfoutput>#md5#</cfoutput>
Hope it helps. Cheers, Mark
Cheers
ST
I haven't tested this but I'm pretty sure that this will work for any algorithm that Java supports. You just need to know the standard names, and there is a java reference here:
http://java.sun.com/j2se/1.4.2/docs/guide/security...
If you change this line:
<cfset var md5 = createObject("java","java.security.MessageDigest").getInstance("MD5")>
to this:
<cfset var md5 = createObject("java","java.security.MessageDigest").getInstance("SHA-1")>
Then it should work - I would also change the md5 variable name to something more sensible.
Let me know how you go.
Cheers,
Mark
I was intrigued so had a quick look - the crypto CFC is now updated to pass through an optional algoritm parameter - everything else works as before and it defaults to MD5.
The reference for the java names is here:
http://java.sun.com/javase/6/docs/technotes/guides...
The new code is here:
https://developer.lynchconsulting.com.au//svn/open...
Cheers,
Mark