WiKID soft tokens

I promised Nick Owens at WiKID Systems a response and it is long overdue. Nick commented on my "soft tokens aren't tokens at all" post:

Greetings. I too have posted a response on my blog. It just points out that our software tokens use public key encryption and not a symmetric, seed-based system. This pushes the security to the initial validation/registration system where admins can make some choices about trade-offs.

Second, I submit that any device with malware on it that successfully connects to the network is bad. So you're better off saving money on tokens and spending it on anti-malware solutions, perhaps at the gateway, defense-in-depth and all.

Third, I point out that our PC tokens provide https mutual authentication, so if you are confident in your anti-malware systems, and are concerned about MITM attacks at the network, which are increasingly likely for a number of reasons, you should consider https mutual auth in your two-factor thinking.

Here's the whole thing:
On the security of software tokens for two-factor authentication
and thanks for stimulating some conversation!

Here is their whitepaper on their soft token authentication system.

Unfortunately, I would like to point out that WiKID is first and foremost vulnerable to the same sort of session stealing malware that Trojan.Silentbanker uses. It doesn't matter how strong your authentication system is when you have a large pile of untrustworthy software in between the user and the server-side application (e.g. browser, OS, third party applications, and all the malware that goes with it). I'll repeat the theme: it's time to start authenticating the transactions, not the user sessions. I went into a little of what that might look like.

Nick is aware of that, which is why he said point number two above. But here's the real problem: the web is designed for dynamic code to be pulled down side-by-side with general data, acquired from multiple sources and run in the same security/trust context. Since our browsers don't know which is information and which is instructions until runtime AND since the instructions are dynamic (meaning they may not be there for the next site visit), how is it NOT possible for malware to live in the browser? I submit that it is a wiser choice to NOT trust your clients' browsers, their input into your application, etc., than to trust that a one time password credential really did get input by the proper human on the other end of the software pile. I suggest that organizations should spend resources being able to detect and recover from security failures (out of band mechanisms come to mind-- a good old fashioned phone call to confirm that $5,000 transaction to a foreign national, perhaps?), rather than assuming the money they invested in some new one time password mechanism exempts them from any such problems.

Microsoft published a document titled "10 Immutable Laws of Security" (nevermind for now that they are neither laws, nor immutable, nor even concise) and point number one is entirely relevant: "Law #1: If a bad guy can persuade you to run his program on your computer, it's not your computer anymore". How does javascript, a Turing Complete programming language, fall into that? If you completely disable script in your browser, most applications break. But if you allow it to run, behaviors you cannot control can run on your behalf. Taking Nick's advice, we should be spending all of your time and resources solving the code and data separation problem on the web, not implementing one time passwords (and I agree with him on that).



Second, I have a hard time calling WiKID a token-- not that it couldn't fit that definition-- it's just that it is a public key cryptography system. I never have referred to a PGP key pair as a token, nor have I heard anyone else. Likewise I don't really ever here anyone say "download this x509 token" ... instead they say "x509 certificate". Smart cards might be the saving grace example that allows me to stretch my mind around the vocabulary; generally speaking, a smart card is a physical "token" and smart card implementations can have a PKC key pair. So, I'll have to extend my personal schema, so to speak, but I guess I'll allow WiKID to fit into the "token" category (but just barely).

The x509 cert example is a great analogy, because under the hood that's basically how WiKID works. Just like an HTTPS session, it swaps public keys (which allows for the mutual authentication) and then a session key is created for challenge/response-- the readout of the "soft token" that the user places into the password form, for example.


There is one concerning issue with WiKID. It uses a relatively unknown public key encryption algorithm called NTRU. NTRU aims to run in low resource environments like mobile phones, which is undoubtedly why WiKID employs it. NTRU is also patented by NTRU Cryptosystems, INC (the patent may have some business/political ramifications similar to PGP's original IDEA algorithm). However, when choosing an encryption algorithm, it is best to use that which has withstood significant peer review. Otherwise, Kerckhoffs' Principle that we have come to know and love as "security by obscurity" will eat us alive when the first decent attack reduces our security to rubble. Googling for "NTRU cryptanalysis" returns around 3,000 hits. Googling for "RSA cryptanalysis" returns around 186,000-- two orders of magnitude higher. This is not the nail in WiKID's coffin, though, but it could be betting the company on Betamax. It is undoubtedly less popular than, say RSA or Eliptic Curve. In most aspects of life, supporting the underdog can result in a great time. Doing it in crypto, however, may not be a good idea.

Before somebody reads the above paragraph and goes in the extreme in either direction, please note my point: the workhorse of WiKID, the NTRU encryption algorithm, has an unknown security value. One could argue that RSA, likewise, has only a mostly known security value, but you decide: "mostly known" or "unknown"? There may not be any problems in NTRU and it may be perfectly safe and secure to use. Conversely it may be the worst decision ever to use it. That's what peer review helps us decide.


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To sum up ... WiKID is cheap, open source, interesting, and ... still vulnerable to malware problems. And don't forget: you have to choose to use a less popular encryption algorithm.

AV Signature False Positives

Kaspersky's AV accidentally identified the Windows Explorer process as malware. The same thing happened to Symantec with their Asian Language Windows customers. And Heise is running an article on how AV vendors' ability to protect has decreased since last year.


The problem with these commercial, signature-based, anti-malware solutions is that they work 1) Backwards, and 2) Blind. They operate "backwards" in the sense that they are a default-allow (instead of default-deny) mechanism-- they only block (unless they screw up like this) the stuff they know all of their customers will think is bad. And they operate "blind" in that they don't do any QA on their code in your environment. If you think about it, it's scary: they apply multiple (potentially crippling as evidenced by these recent events) changes to production systems, in most organizations several times per day without proper change control processes. Besides anti-malware, what other enterprise applications operate in such a six-shooters-blazing, wild west cowboy sort of way?


Surely this is one more nail in the signature-based anti-malware coffin.

Soft tokens aren't tokens at all

The three categories of authentication:

Something you know
Something you have
Something you are

Physical hardware tokens, like RSA's SecurID, fall into the second category of "something you have". Software tokens, also like RSA's software SecurID, pretend to fall into that same category ... but they are really just another example of "something you know".


Physical tokens are designed to be tamper resistant, which is an important property. By design, if a physical token is tampered, the internal storage of the token's "seed record" (symmetric key) is lost, in an attempt to prevent a physical attacker from duplicating the token. [Note the words "tamper resistant" not "tamper proof".]

Soft tokens, however, do not share this property. Soft tokens are comprised of two components: 1) the software application code that implements the one time password function and 2) the seed record used in the application to generate the one time password function's output.

"Perfect Duplication" is a property of the Internet/Information Age that is shaking the world. The Recording/Movie Production Industries are having a hard time fighting perfect duplication as a means to circumvent licensed use of digital media. Perfect duplication can be a business enabler as well, as it is with news syndication services that distribute perfect copies of their stories throughout the far reaches of the world in a matter of seconds. In the case of soft tokens, though, perfect duplication is a deal breaker.

Soft tokens are designed to be flexible. It's difficult to provision a hardware token to an employee halfway around the world the same day of the request, but with soft tokens provisioning is a piece of cake. Likewise, it's easier to recover soft tokens when that same employee is terminated. Soft tokens run on virtually any platform. RSA supports everything from Windows Desktops to Browser Toolbars to Mobile Devices-- all you need to do is import the seed record.

There's the rub ... Distributing the seed record requires a confidential channel to ensure that it is not perfectly duplicated in transit. Distributing seed records to many of the supported platforms of soft token vendors involves plaintext transmission, such as sending the seed record as an email attachment to a Blackberry client. An administrator may provision the seed record encrypted using an initial passphrase that is distributed out-of-band, but it is common practice for seed records and initial passphrases to be distributed side-by-side. Whereas a physical token can only be in one place at a time, a soft token could be perfectly duplicated by an eavesdropper, even complete with its initial passphrase (especially when it isn't distributed out of band). If Alice receives her soft token and changes its passphrase, Eve could keep her perfect copy with the intial passphrase or choose to change the passphrase-- either way, the back end of the one-time-password authentication system will receive a valid token code (time value encrypted with the seed record).

Likewise, a soft token employed on a malware-ridden remote PC could have its stored contents uploaded to an adversary's server, capturing the seed record. If the malware also captures keystrokes (as software keystroke logging is so common these days), then another opportunity for a perfect duplicate exists. Soft tokens are vulnerable to severe distributed key management problems. Bob (the administrator in this case) cannot know if the one time password was generated by Alice's soft token application or Eve's perfect duplicate.

In short, a soft token can prove a user "has" the token, but it cannot prove the user exclusively has the only copy. Therefore, soft tokens are not truly "something you have"; they are "something you know" (i.e. the passphrase to unlock a seed record).

For organizations seeking soft tokens as a method of achieving multi-factor authentication, a password plus a soft token is simply two instances of "something you know". Thus the organization must ask itself: "Does the complexity of properly distributing seed records in a secure channel as well as the expense of managing and supporting the software token application code really provide sufficient benefit over a simple--yet strong-- password only method?" My prediction is the answer to that question will be: "No, it doesn't".

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UPDATED 12/11/2007 - Sean Kline, Director of Product Management at RSA, has posted a response [Thanks for the heads up]. Perhaps we will have some interesting dialog.

Still more separation of code and data

Separating code from data is a HUGE problem (possibly a root of all remote code execution evil). Here's more info, some of it new, some of it very old ...

There's a variety of vulnerabilities discovered recently that all involve document file types that either: A) allow executable code or script (which should be treated as code, not text data) to be embedded within the document, or B) to have buffer overruns because of the complexity of the file types. [Special thanks to the blog post at Hackademix.net for the summary of recent events and for his contribution of NoScript.]
Schneier's blog also pointed readers to a paper from 2002 regarding Multics, an "an operating system from the 1960s, and had better security than a lot of operating systems today" (Schneier).

From the paper on Multics:

"Multics also avoided many of the current buffer overflow problems through the use of three hardware features. First and most important, Multics used the hardware execute permission bits to ensure that data could not be directly executed. Since most buffer overflow attacks involve branching to data, denying execute permission to data is a very effective countermeasure. Unfortunately, many contemporary operating systems have not used the execute permission features of the x86 segmentation architecture until quite recently [17].

Second, Multics virtual addresses are segmented, and the layout of the ITS pointers is such that an overflow off the end of a segment does not carry into the segment number portion. The net result is that addressing off the end of a segment will always result in a fault, rather than referencing into some other segment. By contrast, other machines that have only paging (such as the VAX, SPARC, or MIPS processors) or that allow carries from the page offset into the segment number (such as the IBM System/370) do not protect as well against overflows. With only paging, a system has to use no-access guard pages that can catch some, but not all references off the end of the data structure. In the case of the x86 processors, although the necessary segmentation features are present, they are almost never used, except for operating systems specifically designed for security, such as GEMSOS [32].

Third, stacks on the Multics processors grew in the positive direction, rather than the negative direction. This meant that if you actually accomplished a buffer overflow, you would be overwriting unused stack frames, rather than your own return pointer, making exploitation much more difficult." [Boldface and italics are mine]

Amazing. Three features that most modern OSes still do not have. Note that the "first and most important" feature is that executable code is tagged with the execute bit. While that is not pure separation of code and data, it is an excellent start because it does at least distinguish between with memory objects are code and which are just data. Hence, a char/string based buffer overflow could not result in a remote code execution scenario because the object would not have the execute bit flipped.

To be fair, some OSes have limited support for NX (No Execute) bits (which if you're smart you'll catch that to be "black lists" not "white lists" like Multics uses), but the implementation's quality and thoroughness is typically limited to support from the CPU architecture employed. From the list, though, it looks like a fair number of the 64 bit CPUs are well supported.

Windows Vista will support NX (along with ASLR), but there may be some caveats, such as the typical requirement of vendors to opt-in to use the feature. From AMD:

"For NX to be applied to a given executable, three conditions must be met. First, the processor has to support NX. As mentioned, any AMD64 processor will fill the bill here. Second, EVP support has to be on globally, which will be true for all 64-bit Vista builds and all 32-bit Vista builds unless NX support is explicitly switched off with a boot configuration option. And finally, Vista has to mark all of the program's non-code pages with the NX flag, which is determined by the operating environment (32-bit or 64-bit Vista), boot configuration options, and the program itself."

Overall, that may make a compelling argument to switch to 64 bit architecture.


So, what's today's lesson? Either separate code from data or pay for it eternally as you penetrate and patch.

Separation of Code and Data

One of the most surprising things for a savvy information security practitioner is the continued prevalence of intermingling of code and data in modern information systems. It is as if some mandate dictates that these items must be desegregated. This is the root cause of every buffer overrun/overflow exploit, every XSS or SQL Injection attack, even Microsoft's infamous run of bugs in office documents and images (think GDI). Yet, today, there are simply too many systems that do not properly (if at all) segregate data objects from executable code objects in memory.

Buffer overruns
The gist is that a program allocates memory for a data object (as in "information" of some type), but because of some implementation bug, executable code can be passed to the function instead of data (because the program does not distinguish the two). And eventually for one reason or another, but mainly because the system does not require executable code to be stored in a location with better access control separate from data elements, the data object is unintentionally executed, frequently containing malicious payloads.

Cross Site Scripting
Most cases of XSS are no different. Essentially, data elements (usually expected to be in the form of plain, rich, or html text) are uploaded containing client-side executable scripts with malicious payloads.

SQL Injection
Again, same song, second verse, only this time the "data" is really malicious SQL commands uploaded as text.


Why, if the top technical causes of malware all share the commonality of not properly segregating code and data, do we not yet have systems that build this property in?


Excellent question, of course. The current-generation attempts to solve this include Address Space Layout Randomization (ASLR), and, more formidably, No Execute (NX). Windows Vista's downfall, of course (all debate on licensing aside) is that for backwards-compliance's sake old applications cannot be forced to segregate their memory objects. And the patterns of lazy or ignorant developers yet again plague both the consumer and the enterprise.


Perhaps one day we'll get this right.