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.

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