Evan Schuman's StorefrontBacktalk

Where before retailers and processors could review, say, CERT bulletins, they now need to consider their own rankings and take actions based on their own risk assessment. The guidance says, “At minimum, the most critical, highest risk vulnerabilities should be ranked as High.”

The other related “Evolving Requirement” is a new 6.5.6. This sub-requirement is part of a revamped Requirement 6.5 that in PCI Version 2 addresses all software applications not just Web-facing ones, as was the case previously. The new requirement says you develop applications to avoid or prevent those high-ranking vulnerabilities you identified in Requirement 6.2.

The risk in each of these quasi-requirements is that some merchants and processors may be tempted to identify and rank only those vulnerabilities that will cause their servers to catch fire as “high” and rank everything else “low.” I really hope I’m wrong on that one.

Sometimes it isn’t what Version 2.0 says that is interesting, but what it doesn’t say. For example, Requirement 2.1.1, which addresses wireless security and was re-subdivided, no longer contains any reference to WPA or WPA2. Where it used to say, “Firmware on wireless devices is updated to support strong encryption for authentication and transmission over wireless networks (for example, WPA/WPA2),” it now says just to “Verify firmware on wireless devices is updated to support strong encryption for authentication and transmission over wireless networks.” The reference to any specific encryption technology has been removed.

The reason for eliminating the reference to WPA in particular is in the Summary of Changes document: “[The PCI Council] removed reference to WPA, as this is no longer considered strong encryption on its own.” The previous version eliminated WEP as an option for protecting wireless networks and, because WPA has been regarded as inadequate for some time, it looks like WPA has bitten the dust, too. The two messages for retailers with in-scope wireless networks seem to be either implement WPA2 fast or give some serious thought to whether wireless networks are appropriate for transmitting cardholder data. You may want to include wireless in your risk analysis (Requirement 12.1.2), too.

Requirement 3.4 provides new guidance on hashing. The text of the new requirement states that if hashed and truncated versions of the same PAN are present in the cardholder data environment, “additional controls should be in place to ensure that the hashed and truncated versions cannot be correlated to reconstruct the original PAN.” Unfortunately, there is not much information on what those controls should be.

The reason for this revised requirement is that if the bad guys get both a truncated PAN and the hashed version of that same PAN, fairly trivial techniques can be used to reconstruct the PAN. Depending on how you’re using these pieces of data, it may be a significant challenge to separate them and add sufficient “additional controls.” I can only hope that the Council will release some formal guidance on what these controls should be.