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Public-Key Encryption

Making strong encryption nearly painless

How secure are your applications? Public-Key encryption may be the solution when security really matters.

If you have developed an application that requires user authentication, you have undoubtedly wrestled with varying levels of security. At a basic level, most security models revolve around membership, authentication, and authorization functions. Secure socket layers (SSL) is a popular method for securing the transmission of data between Web server and client. ColdFusion MX and ColdFusion 6.1 have very good integration with Java's Secure Socket Extensions Library, which is capable of 2048-bit encryption. While the transmission of the data over the Internet via SSL helps secure against electronic eavesdropping, the data stored in your applications may still be at risk.

The storage of passwords is a prime example of this security risk. If your database is compromised in some way, the attacker has access to all user accounts and passwords. As a result, programmers have developed various techniques for addressing this issue. ColdFusion itself has an encryption function available - encrypt() - that utilizes an XOR (exclusive OR) algorithm to generate a pseudo 32-bit symmetric key. Another method involves using ColdFusion's hash() function. The hash() function is based on an MD5 (message digest version 5) 128-bit hash algorithm that converts strings into 32-bit hexadecimal "fingerprint" or "message digest" representations of the original string. A stronger variant of this method involves introducing salt - a random string of some length - and concatenating it with the password before performing the hash function.

While storing an encrypted or hashed version of passwords using ColdFusion's built-in functions is a good practice, these methodologies fall a bit short when security is a real issue. The hash() function is a one-way encryption algorithm that can be decrypted only by brute force. MD5 hashing as a method of securing passwords and other data falls apart when one does a Google search of "MD5 crack." For unsalted hashes, the time needed to crack a single MD5 hash online is about 40 minutes (http://passcracking.com). Depending on your personal computer speeds, this can be done faster with a tool like md5crack (www.checksum.org/download/MD5Crack). In fact, in 1994 Paul van Oorschot and Mike Wiener showed that a brute force attack on a 128-bit hash function requires 264 (2.1019) evaluations to crack; at the time such a crack would take less than a month with a $10 million investment in hardware.

To deal with the shortcomings of 128-bit hash functions, stronger encryption algorithms have been invented. Today's 160-bit encryption algorithms such as SHA1 (secure hash algorithm, www.w3.org/PICS/DSig/SHA1_1_0.html) and RipeMD160 (www.esat.kuleuven.ac.be/~bosselae/ripemd160.html) increase the time required for a brute force attack. For areas where a 160-bit hash is still not strong enough, SHA also comes in 256-bit, 384-bit, and 512-bit data lengths for added security in one-way encryption.

Because hash() is a one-way encryption algorithm, it is most appropriate when text does not need to be read (as in the case of passwords). By contrast, the encrypt() function utilizes symmetric-key cryptography, meaning that both the sender and receiver of the string share a common key used to encrypt and decrypt the string. Thus, the private key must at some point be transferred in some secure way, and is only effective if the symmetric key is kept secret.

In ColdFusion, this transfer is done on the server in memory when a page with the encrypt() function is requested, which keeps the transmission of the passphrase reasonably secure. Yet, in the case of encrypt(),the key is actually passed in both the encrypt() and decrypt() functions as plain text:

<cfscript>
   password = "Th1s !s A R@alLy str0nG pA5Sw0rD!";
   symmetricKey = "pa$sPhrAs3 f0r 3ncRypt1ng p4s$w0rDs";

   encrypted = encrypt(password, symmetricKey);
   decrypted = decrypt(encrypted, symmetricKey);
</cfscript>

<cfoutput>
<p>#encrypted# <br/> #decrypted#</p>
</cfoutput>

Depending on who has access to your code, this could be a recipe for disaster.

When you need to be able to encrypt and decrypt, additional steps must be taken. ColdFusion's encrypt() function can be decrypted, but the key must be passed in the code on the server, causing a security issue (plus encrypted data placed on the Web can be fairly easily cracked using any number of free tools available on the Internet.

An alternative to ColdFusion's private-key encryption method is public-key encryption. Public-key encryption - or asymmetric encryption - requires two keys - one private and one public. Data encrypted with your public key can be decrypted only with your private key, allowing you to freely distribute your public key in a non-secure manner (i.e., as clear text posted on a Web page). Asymmetric encryption uses longer algorithms for calculating file fingerprints than symmetric encryption algorithms, and is effective for generating significantly obfuscated data. As a brief side note, these algorithms are processor intensive, so using public key encryption may not be appropriate for very large files.

Unfortunately, in order to take advantage of asymmetric encryption in ColdFusion, you must look beyond built-in ColdFusion tools. The two big players in the realm of public-key cryptography are Pretty Good Privacy (PGP; www.pgp.com) and GNU Privacy Guard (GnuPG; www.gnupg.org). "GnuPG is a complete and free replacement for PGP," and since GnuPG does not depend on the patented International Data Encryption Algorithm (IDEA), there are no restrictions on its use, nor are there any licensing fees for integrating GnuPG into your applications. This last fact makes it an attractive candidate for developers, and is used in the examples for this article. Along with the strong two-way encryption algorithms (1024-bit DSA and ElGamal), GnuPG also supports stronger hashing functions (SHA1, RIPEMD160, and SHA256) for your one-way encryption needs.

More Stories By Wayne Graham

Wayne Graham is a systems administrator at the College of William and Mary's Earl Gregg Swem Library. Wayne is also the co-manager of the Williamsburg Macromedia User's Group and has been developing with ASP, Java, and ColdFusion since 2001.

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Most Recent Comments
Thomas Gorgolione 07/23/08 05:05:27 PM EDT

You have to compile the code manually from the zip file (see post #5). I did that already, so if you want you can just download it here:

www.tgorg.com/etc/GnuPG.jar

Jeff 01/31/08 08:07:47 AM EST

Does anyone have the GnuPG.jar file? I found the CF component but that still needs the GnuPG.jar file to operate and the link in the article to get GnuPG.jar does not work.

Shaun 09/04/07 02:21:25 PM EDT

Found this:
http://res.sys-con.com/story/46359/source.html

William Broadhead 07/21/05 03:00:51 PM EDT

Good story. Very informative. One thing I would note is that in cf using the encrypt/decrypt: You don't have to, and shouldn't include the actual key in your code, NOR in your Database... A tecnnique I use is to store the key in a text file on the server in a directory that is accessible to coldfusion but NOT part of the http accessible directory. Using cffile you can read and load the information in the file to memory as an application key to use for hashing passwords while never having the key in your code nor in your database. Although obviously, as the article points out, security can never be completely infallible, this can reduce the capacity of your data to be compromised if you did somehow lose a copy of your database or page code, you would need also need to lose the file for someone to put it all together...

Mark 07/14/05 01:53:05 PM EDT

Great article, very well written.

Brad 03/28/05 10:13:32 AM EST

Great Article, convinced my peers to use this instead of upgrading to CF7Mx.

As for the gentleman looking for the source, click the Source Code link located under Related Sites. Scroll down... you're welcome.

Nguyen Tran 03/21/05 10:50:00 AM EST

Where to download the file? GnuPG.jar

The link you provided as:
www.sys-con.com/coldfusion/sourcec.cfm
Point to the page at:
http://sys-con.com/magazine/archives.cfm?id=5

On this page, there is no link to download the file GnuPG.jar

Please give us the link to download the file GnuPG.jar

Thank you

Tom 02/08/05 06:05:04 AM EST

hello,

i´ve the same problem: where is gnupg.jar?
regards, tom

Shane 12/16/04 11:14:17 AM EST

nevermind.... I found it.

Shane 12/16/04 11:09:21 AM EST

Great article. I've been looking forward to trying this out but haven't been able to find the gnupg.jar file. Am I overlooking it somewhere? Please advise.

Thanks.