Archive for the 'Requirement 12 – Encrypt sensitive traffic over public networks' Category


Council Surveys QSAs On SSL

This message popped into my inbox late yesterday.


The survey in question contains the following questions.


All of my clients have gotten rid of SSL on their public facing Web sites.

The dilemma we have is that while SSL is dead, it is baked into so many products and appliances.  My clients are therefore stuck with appliances and software products that have SSL hard coded into them.  As a result, they will be dependent on their vendors to convert to TLS.

That said, what is the risk of using SSL internally?  Not a good practice, but truthfully, what is the risk?

In my opinion, using SSL internally for the next 12 to 24 months would not be the end of the world as long as it does not become a significant attack vector.

It will be interesting to hear the results of this survey.


SSL Is Officially Declared Dead

On January 30, 2015, QSAs received the latest edition of the Council’s Assessor Newsletter.  Buried in that edition was the following statement.

Notice: PCI DSS and PA-DSS v3.1 Revisions Coming

In order to address a few minor updates and clarifications and one impacting change, there will be a revision for PCI DSS and PA-DSS v3.0 in the very near future. The impacting change is related to several vulnerabilities in the SSL protocol. Because of this, no version of SSL meets PCI SSC’s definition of “strong cryptography,” and updates to the standards are needed to address this issue. (Highlighting emphasis added by the PCI Guru)

We are working with industry stakeholders to determine the impact and the best way to address the issue. While we do not have the final publication date, our goal is to keep you apprised of the progress and to provide you with advanced notification for these pending changes. We are also preparing several FAQs that will accompany release of the revised standards.

Should you have any questions, please contact your Program Manager.”

Because the announcement was titled about the coming v3.1 revisions to the PCI DSS and PA-DSS standards, I am sure a lot of QSAs missed this pronouncement.

Not that this should be a surprise to any QSA as the POODLE vulnerability effectively killed SSL.  The Council has now officially announced that SSL is no longer deemed to be strong cryptography.

Therefore, those of you still using SSL to secure transmissions containing cardholder data (CHD) need to stop that practice as soon as possible and convert to TLS or IPSec.

UPDATE: On February 13, 2015, the PCI SSC issued an update to their original announcement in the Assessor Newsletter.


Encryption Basics

NOTE: This is a revised version of my original post to reflect readers concerns regarding statements made that do not reflect best practices surrounding encryption key management.  A big thank you to Andrew Jamieson who reviewed and commented on this revised posting.

During the last couple of years, I have run into more and more questions regarding encryption and encryption key management than I thought existed.  As a result, I have come to the realization that, for most people, encryption is some mystical science.  The stories of the Enigma machine and Bletchley Park have only seemed to add to that mysticism.  Over the years, I have collected my thoughts based on all of the questions and developed this distilled and very simplified version of guidance for those of you struggling with encryption.

For the security and encryption purists out there, I do not represent this post in any way, shape, or form as the “be all, to end all” on encryption.  Volumes upon volumes of books and Web sites have been dedicated to encryption, which is probably why it gets the bad reputation it does as the vast majority of these discussions are about as esoteric as they can be.

In addition, this post is written in regards to the most common method of encryption used in encrypting data stored in a database or file and that is the use of an encryption algorithm against a column of data or an entire file.  It does not cover public key infrastructure (PKI) or other techniques that could be used.  So please do not flame me for missing your favorite algorithm, other forms of encryption or some other piece of encryption minutiae.

There are all sorts of nuances to encryption methods and I do not want to cloud the basic issues so that people can get beyond the mysticism.  This post is for educating people so that they have a modicum of knowledge to identify hyperbole from fact.

The first thing I want to clarify to people is that encryption and hashing are two entirely different methods.  While both methods obscure information, the key thing to remember is that encryption is reversible and hashing is not reversible.  Even security professionals get balled up interchanging hashing and encryption, so I wanted to make sure everyone understands the difference.

The most common questions I get typically revolve around how encryption works.  Non-mathematicians should not need to know how an encryption algorithm works, that is for the experts that develop and prove that they work.  In my opinion, unless you are a mathematician studying cryptography, I recommend that people trust the research conducted by the experts regarding encryption algorithms.

That is not to say you should not know strong cryptography from weak cryptography.  I am just suggesting that the underlying mathematics that defines a strong algorithm can be beyond even some mathematicians, so why we expect non-mathematicians to understand encryption at this level is beyond me.  My point is that the algorithms work.  How they work is not and should not be a prerequisite for management and even security professionals to using encryption.

This leads me to the most important thing people need to know about encryption.  If you only take away one thing from this post, it would be that strong encryption comes down to four basic principles.

  • The algorithm used;
  • The key used;
  • How the key is managed; and
  • How the key is protected.

If you understand these four basic principles you will be miles ahead of everyone else that is getting twisted up in the details and missing these key points.  If you look at PCI requirement 3, the tests are structured around these four basic principles.

On the algorithm side of the equation, the best algorithm currently in use is the Advanced Encryption Standard (AES).  AES was selected by the United States National Institute of Standards and Technology (NIST) in 2001 as the official encryption standard for the US government.  AES replaced the Data Encryption Standard (DES) that was no longer considered secure.  AES was selected through a competition where 15 algorithms were evaluated.  While the following algorithms were not selected as the winner of the NIST competition, Twofish, Serpent, RC6 and MARS were finalists and are also considered strong encryption algorithms.  Better yet, for all of you in the software development business, AES, Twofish, Serpent and MARS are open source.  Other algorithms are available, but these are the most tested and reliable of the lot.

One form of DES, Triple DES (3DES) 168-bit key strength, is still considered strong encryption.  However how long that will remain the case is up for debate  I have always recommended staying away from 3DES 168-bit unless you have no other choice, which can be the case with older devices and software.  If you are currently using 3DES, I would highly recommend you develop a plan to migrate away from using it.

This brings up another key take away from this discussion.  Regardless of the algorithm used, they are not perfect.  Over time, encryption algorithms are likely to be shown to have flaws or be breakable by the latest computing power available.  Some flaws may be annoyances that you can work around or you may have to accept some minimal risk of their continued use.  However, some flaws may be fatal and require the discontinued use of the algorithm as was the case with DES.  The lesson here is that you should always be prepared to change your encryption algorithm.  Not that you will likely be required to make such a change on a moment’s notice.  But as the experience with DES shows, what was considered strong in the past, is no longer strong or should not be relied upon.  Changes in computing power and research could make any algorithm obsolete thus requiring you to make a change.

Just because you use AES or another strong algorithm does not mean your encryption cannot be broken.  If there is any weak link in the use of encryption, it is the belief by many that the algorithm is the only thing that matters.  As a result, we end up with a strong algorithm using a weak key.  Weak keys, such as a key comprised of the same character, a series of consecutive characters, easily guessed phrase or a key of insufficient length, are the reasons most often cited as why encryption fails.  In order for encryption to be effective, encryption keys need to be strong as well.  Encryption keys should be a minimum of 32 characters in length.  However in the encryption game, the longer and more random the characters in a key the better, which is why you see organizations using 64 to 256 character long random key strings.  When I use the term ‘character’ that can be printable characters of upper and lower case alphabetic as well as numeric and special characters.  But ‘character’ can also include hexadecimal values as well if your key entry interface allows for hexadecimal values to be entered.  The important thing to remember is that you should ensure that the values you enter for your key are as hard to guess or brute force as maximum key size of the algorithm you are using.  For example, using a seven character password to generate a 256 bit AES key does not provide for the full strength of that algorithm.

This brings us to the topic of encryption key generation.  There are a number of Web sites that can generate pseudo-random character strings for use as encryption keys.  To be correct, any Web site claiming to generate a “random” string of characters is only pseudo-random.  This is because the character generator algorithm is a mathematical formula and by its very nature is not truly random.  My favorite Web site for this purpose is operated by Gibson Research Corporation (GRC).  It is my favorite because it runs over SSL and is set up so that it is not cached or processed by search engines to better guarantee security.  The GRC site generates 63 character long hexadecimal strings, alphanumeric strings and printable ASCII strings, not numerical strings provided by other random and pseudo-random number generator sites.  Using such a site, you can generate keys or seed values for key generators.  You can combine multiple results from these Web sites to generate longer key values.

In addition, you can have multiple people individually go to the Web site, obtain a pseudo-random character string and then have each of them enter their character string into the system.  This is also known as split key knowledge as individuals only know their input to the final value of the key.  Under such an approach, the key generator system asks each key custodian to enter their value (called a ‘component’) separately and the system allows no key custodian to come into contact with any other custodian’s component value.  The key is then generated by combining the entered values in such a way that none of the individual inputs provides any information about the final key.  It is important to note that simply concatenating the input values to form the key does not provide this function, and therefore does not ensure split knowledge of the key value.

Just because you have encrypted your data does not mean your job is over.  Depending on how your encryption solution is implemented, you may be required to protect your encryption keys as well as periodically change those keys.  Encryption key protection can be as simple as storing the key components on separate pieces of paper in separate, sealed envelopes or as high tech as storing them on separate encrypted USB thumb drives.  Each of these would then be stored in separate safes.

You can also store encryption keys on a server not involved in storing encrypted data.  This server should not be any ordinary server as it needs to be securely configured and very limited access.  Using this approach is where those key encryption keys (KEK) come into play.  The way this works is that each custodian generates a KEK and encrypts their component with the KEK.  Those encrypted components can then be placed in an encrypted folder or zip file where computer operations have the encryption key.  This is where you tend to see PGP used for encryption as multiple decryption keys can be used so that in an emergency, operations can decrypt the archive and then the key custodians or their backups can decrypt their key components.

Finally, key changes are where a lot of organizations run into issues.  This is because key changes can require that the information be decrypted using the old key and then encrypted with the new key.  That decrypt/encrypt process can take days, weeks even years depending on the volume of data involved.  And depending on the time involved and how the decrypt/encrypt process is implemented, cardholder data can potentially be decrypted or exposed because of a compromised key for a long period of time.

The bottom line is that organizations can find out that key changes are not really feasible or introduce more risk than they are willing to accept.  As a result, protection of the encryption keys takes on even more importance because key changes are not feasible.  This is another reason why sales of key management appliances are on the rise.

That is encryption in a nutshell, a sort of “CliffsNotes” for the non-geeky out there.  In future posts I intend to go into PKI and other nuances to encryption and how to address the various PCI requirements in requirements 3 and 4.  For now, I wanted to get a basic educational foundation out there for people to build on and to remove that glassy eyed look that can occur when the topic of encryption comes up.


Extremely Mobile Payment Processing

In a previous post I discussed mobile computing and PCI compliance.  In the last couple of weeks I have been questioned about using mobile devices such as smartphones and Wi-Fi enabled PDAs as payment terminals and I thought this particular incarnation of mobile computing deserved an in-depth look.

Pay attention to that Apple iPhone advertisement.  If you notice in one of their advertisements they show a person processing a credit card payment on their iPhone.  As Apple likes to say, “There’s an app for that.”  However, it is not just Apple that has a payment application for a mobile device; there are also payment processing applications for Windows Mobile environments.  There are also proprietary solutions from VeriFone and the like.  Some of these applications are PABP and/or PA-DSS certified.  Devices from VeriFone and the like are PCI PTS certified, but the iPhone and other cellular phones as well as PDAs are not PCI PTS certified devices.

So when the pizza delivery person shows up at your door and wants to swipe your credit card through their mobile device, how do you know that it is safe?  You likely will not know.

The security surrounding the telecommunications used by these devices is the easiest thing to discuss.  All of the devices I have been able to examine use telecommunications methods that are encrypted either by SSL v3 or TLS.  The cellular network and Wi-Fi are just used as the conduit and are not relied upon to provide any security.

Do not assume that VeriFone and the like are meeting all of the PCI standards.  While their mobile payment terminals are PCI PTS certified, the application software in those devices is not PA-DSS certified.  I pointed to the flaws in these devices in a previous post.

But there are bigger problems lurking with the iPhone.  Ask any computer forensic examiner about the iPhone and they will talk at length about the fact that the iPhone has a number of “features” that make security and privacy things of the past.  From a PCI compliance perspective, some of the more problematic issues are as follows.

  • Deleted information does not physically get deleted.  In some cases, deleted data can remain on an iPhone for up to six months or even more depending on use.
  • The iPhone has a built-in keyboard logger, so anything typed into it is recorded.
  • While it is not certain that card swipes would be retained on the iPhone, given all of the other information it retains, it is highly likely that such information would also be retained.

As a result, using the iPhone as a payment processing platform is probably not a good idea until it is certified.

So what, if anything, are the PCI SSC and/or the card brands doing about this situation?  As much as they can, given that these solutions are popping up faster than they can identify them.  The problem is that the developers of these applications are usually unaware that they are required to comply with various PCI standards.  And since the developer is responsible for certifying their solution unless they get ‘ratted out’, the solution will not get certified.  So it is up to the application developer and the merchants to ensure that an application is properly certified.  If that is not worrisome enough, the cost involved in certifying such an application would likely raise the cost of that solution to a point where it would not be economical to the merchant or salesperson.

January 2022