Message-ID: <20060914020551.22313.qmail@securityfocus.com>
Date: 14 Sep 2006 02:05:51 -0000
From: vin@...world.com
To: bugtraq@...urityfocus.com
Subject: Re: RSA SecurID SID800 Token vulnerable by design

On Bugtraq and several other security forums, Hadmut Danisch <hadmut@...isch.de>, a respected German information security analyst, recently published a harsh critique of one optional feature in the SID800, one of the newest of the six SecurID authentication tokens -- some with slightly different form-factors, others with additional security functions -- sold by RSA Security, Inc.  It's raised quite a stir, and I'd like to respond.

A personal authentication token, by classical definition, must be physical, personal, and difficult to counterfeit.  The most popular implementations in computer security move the calculation of a pseudo-random authentication code -- a so-called "One-Time Password," or OTP-- off an employee's PC and into a hand-held hardware fob, small enough to be attached to a personal key chain.

RSA's mainstay token, the SID700 SecurID -- millions of which are used in over 20,000 enterprise installations worldwide, including many government agencies and financial institutions -- use AES (the US cryptographic standard) to process Current Time and a 128-bit token-specific secret to generate and continuously display a series of 6-8 digit (or alphanumeric) OTP "token-codes" which change every 60-seconds, and remain valid only for a couple of minutes.

In practice, a RSA authentication server can then independently calculate the token-code that is appearing on a specific SecurID at this particular moment; compare that against an OTP submitted by a pre-registered user, and validate a match.  RSA, which first introduced the SecurID in 1987, has always insisted on the necessity of "two-factor authentication" (2FA), where a remote RSA authentication server must validate both a SecurID token-code (evidence of "something held") and a user-memorized PIN or password ("something known.")

A stolen password can be reused indefinitely to masquerade as the legitimate user, often with the victim wholly unaware. A token-generated OTP, valid only briefly, is a far more robust authenticator.  With 2FA, if a SecurID is stolen or lost, it still can't be used to obtain illicit access to protected resources without the second secret: the user's memorized PIN or password.

The elegant simplicity of the traditional SecurID -- and patents on the mechanism by which the "drift" in each individual SecurID's internal clock is tracked by the RSA authentication server -- has allowed RSA's "time-synched" SecurID to dominate the market niche for hand-held OTP authentication devices for 20 years.

In a typical installation, anyone seeking to log on to a protected PC or network, or to access restricted online resources, must manually type in the OTP currently displayed on the SecurID -- as well as his memorized PIN or password -- to have his identity and access privileges validated. Network applications handle the combined SecurID "pass-code" like any long traditional password. The link between the user and the RSA infrastructure is often, but not always, an encrypted VPN channel. That's a local decision. Data exchanges between the RSA agent  and RSA authentication server -- which typically means between one of the 350-odd "SecurID-aware" network applications and the RSA Authentication Manager, using RSA's own protocol -- are always fully encrypted.

Mr. Danisch is an admirer of the classic SecurID (SID700), RSA's traditional hand-held token. His ire is directed at one of the two new hybrid SecurID designs that RSA has recently offered in an attempt to respond to new requirements in the boisterous and rapidly-evolving market for what's called "strong authentication."

With the nascent prospect of a new billion-dollar market in consumer authentication for financial services boosted by US federal regulatory initiatives, RSA announced the SecurID Signing Token, the SID900. The SecurID Signing Token still has a time-synched OTP, but RSA added a keypad and a challenge/response function which successively authenticates the user, the remote server, and a specific financial transaction, before the transaction (e.g., a funds transfer) is executed.

On the other side of the market -- where again US laws and federal regulatory initiatives have boosted demand for internal controls and more accountability measures in enterprise IT -- RSA has introduced the SID800, another hybrid SecurID, to meet the requirements of organizations that want to move into a full public key infrastructure (PKI.)

The SID800 SecurID is a multi-function authentication and cryptographic device that combines, in a single DPA-resistant token, the mobility and availability of the classic hand-held SecurID, as well as a "smart chip" that implements v2.1.1 Java tech (essentially a "virtual smart card") in a USB format. It looks like a slightly smaller version of the classic SecurID key fob, with a USB plug jutting out at one end. It can carry up to seven X.509 digital certificates for PKI, as well as account information and complex passwords for up to three Windows accounts. The SID800's lithium battery allows it to continuously generate and display 60-second SecurID OTPs for up to five years.

The SID800 "smart chip" has the typical load of standards-compliant smart card functionality: ANSI X9.31 PRNG, client-side PKI support including key generation for DES/3DES and 1024-bit RSA Public Key Cryptography, SHA-1 hashing, and 1024-bit RSA digital signatures.To access its local cryptographic services (key generation, authentication, file encryption, digital signatures, etc.) and its X.509 certificates -- complex resources that require a circuit-to-circuit connection and interactive data exchanges -- the SID800 SecurID can be plugged directly into a PC's USB port.

None of these features -- none of the SID800's cryptographic resources -- were of apparent interest to Mr. Danisch. He ignored them all when he denounced the SID800 as "vulnerable by design."

The classic SecurID, declared Mr. Danisch on the Cryptography mailing list, "is a smart device which provides a reasonable level of security in a very simple and almost foolproof way...."

"It's a pity," he added, "to see it weakened without need..." The traditional SecurID has the advantages (and disadvantages) of an "air gap." With no direct circuit connection to the user's PC or client terminal, it has no direct vulnerability to the various classes of malicious or larcenous malware which -- Mr. Danisch warns -- can potentially overwhelm and totally corrupt PCs, and particularly Windows PCs.

What particularly disturbs Mr. D is one option among in the SID800 SecurID features which allows RSA's local client software to poll and retrieve a single OTP from the token when the SID800 is plugged into the PC's USB port.  Given the potential for malicious malware to invade and take control of any Windows PC -- malware that can seize and misuse both the user's PIN and an OTP fresh from the USB bus -- it was irresponsible, Danisch suggests, for RSA to make such a option available to its customers.

There are actually two versions of the SID800 sold by RSA.  In one version, there is none of the fancy new OTP functionality that worries Mr. D.  In this model, the only way to use the SecurID's OTP is the old-fashioned way: to read the LCD and type it (and the user's PIN) at the keyboard.

In the second version of the SID800 -- an option selectable by local management pre-purchase, and burnt into the token's USB firmware by RSA -- the user can select a menu in which he instructs the SecurID to load one OTP token-code directly into the paste buffer, presumably for immediate use. Since internal access to the SecurID's OTP via the USB bus makes it a potential target for "malware or intruders on the computer," claimed Mr. Danisch, "This is weak by design."  I beg to differ. Effective IT security is about an appropriate balance, not walls of iron or stone.

Can this token-code in the paste buffer be misused? Not likely, even if it is immediately stolen by malware and immediately used for some nefarious purpose.  A SecurID token-code can only be used once; no replay is allowed.  As a defense against race attacks, the RSA Authentication Manager will also automatically reject both of two identical token-codes submitted roughly simultaneously -- even if both are accompanied by the proper PIN -- and log it for investigation by the security manager. If the legitimate user can use the token-code, he effectively preempts any misuse of that OTP by a hostile party or malware.

Could hostile malware independently execute the menu request for a new token-code -- essentially instruct a token plugged into the USB port to produce a new token-code, without the knowledge of the user -- and then swipe it, directly or from the paste buffer? Could malware collect the PIN and logon data of any authentication process with a keyboard logger? Unfortunately, it could.  Mr. Danisch raises a valid concern.

The cryptographic functionality of any smart card -- which typically includes authentication, encryption, digital signatures, etc. -- can be initialized and misused by a powerful hostile agent which took control of the user's PC and snatched the user's password.  Just as -- although Mr. Danisch didn't mention this -- the "virtual smart card" in the SID800, or any similar UBB device, could be initialized and misused.

The level of malware penetration that Mr. D presumes could corrupt the client authentication and cryptographic functions in any contemporary PKI environment, certainly any Windows-based client-side SSL. (See: "Keyjacking: the surprising insecurity of client-side SSL," by Marchesini, Smith, and Zhao at <http://www.cs.dartmouth.edu/~sws/pubs/msz05.pdf>.)

Mr. Danisch denounces RSA for implementing an optional ease-of-use feature, just because it effectively reduces the implicit security of OTP authentication to no more than what is provided by any PKI smart card environment. Some -- but not necessarily me -- might suggest that this is carrying an appreciation of the unique and sterling qualities of the classic SecurID's OTP a bit far.

This has been an ongoing debate within the RSA user community for the past year, where some of the language used in declaring opinions is not always as civil or restrained as that used by Mr. Danisch.  It is not yet clear how the market's choices and concerns will affect the next version of the SID800's firmware, expected later this year -- but it seems unlikely that either of the two SID800 versions will be removed from RSA's sales list.

In security, ease-of-use (which usually implies internal complexity) is often the enemy of security. Yet, any enhancement in ease-of-use which will have little or no impact on overall system security is something of a Holy Grail for both InfoSec vendors and local IT managers.

Some organizations choose to use SID800 SecurIDs which offer RSA's "OTP paste" feature, others do not. Those who don't are presumably acting on the basis of a risk analysis of their environment that determines that the advantages of enhanced usability do not justify the risks it entails.  Many of those, I presume, have concerns similar to those of Mr. Danisch.

If the hostile malware can wait and capture the initiation password off the keyboard, it can ask for anything the password can authorize. From the SID800. From any smart card. From any application. From any network resource. This is not a new insight.  (Ironically, the SID800's OTP output to the USB bus is relatively more difficult to misuse, since it is time-constrained, while stolen smart card functionality typically is not.)

Obviously, if a hostile enemy can load malware that "owns" your PCs, untrustworthy user authentication is only the beginning of your problems.

If the enemy "owns" your Windows box today -- or any other computer, for that matter -- he probably totally controls everything that passes through it, and all devices connected to it.  Although the firmware in a smart card -- or in USB plugs like the SID800 which offer "virtual smart cards" -- supposedly won't allow the PC to directly access the token's internal secrets, a computer under the control of a hostile party can doubtless gain illicit access to the cryptographic services provided by those devices.

Assuming imperfect defenses in any given technical context -- certainly true with the current Microsoft Windows OS, the leading browsers, and the protocols now in use for both secure data transfer and authentication -- the industry consensus calls for multiple defensive layers. Where one defensive layer leaves a gap, another will often overlap to cover it. The logic of such an approach is based on gritty experience: there is no such thing a perfect security!

Mr. Danisch bemoans -- as do other fretful traditionalists like myself, including many who work for RSA -- the loss of the "air gap," the isolation of the SecurID's OTP generation from the potentially corrupted PC and network.  (A networked device will never be as transparent as the classic OTP token, where everybody knows exactly what the SecurID is doing, and can be certain that it is doing no more than it is expected to do. The elegance of simplicity.)

Others -- including many fretful traditionalists -- celebrate (despite imperfect implementations, despite many inherently untrustworthy operational environments) the powerful security utilities which become available with interactive PKI, which RSA pioneered with its work on the seminal Public Key Crypto Standards (PKCS) and the revolutionary RSA public key cipher which is critical to so much of today's network security services.

The two hardest things to do in computer security are (A) to create a perfectly secure technical infrastructure, and (B) to second-guess the CIO, CISO, or local system administrator who has the responsibility to identify his assets, understand his risks, and select where and how to balance his investments in usable functionality and information security.

Since no one today argues that perfect security is attainable, security mavens like Mr. Danisch (and myself) are forever occupied with the second task. Yet, as Courtney's First Law -- codified 40 years ago by IBM's Bob Courtney, one of the pioneers in computer security -- puts it: "Nothing useful can be said about the security of a mechanism except in the context of a specific application and a specific environment."

Information security vendors like RSA attempt to respond to the perceived market requirements, juggling concerns about risk, liability, and cost against demands for functionality, flexibility, and accessibility.  When relative security is slightly compromised for a perhaps critical enhancement in ease-of-use, it seems smart to at least give the buyers the option.  That leaves the critical judgment to the professionals who know their environment, their real risks, and their people, best.

Lecturing CIOs about the relative importance of security threats -- when they have to get real work done in an imperfect universe -- is as presumptuous as it is almost surely ill-informed.  Hectoring vendors who respond to demands from their customers for alternative ways to address security issues -- some admittedly more or less robust than others -- is far more appropriate. In that sense, debates that arise when critics like Mr. Danisch forcefully state their case are useful, even necessary.

It is no secret that Windows and the browsers have design flaws.  Client-side SSL still has some major architectural issues, particularly in Windows. It is no secret that PC users today need a safer place -- some sort of restricted input environment, inaccessible to all but the local user -- by which they can submit authentication calls to an application over a trusted path. It is no secret that network protocols require new IETF initiatives to better secure them against attempts to corrupt them for illicit gain. It is no secret that simple authentication protocols must today often be supplemented by some form of mutual authentication, or that high-value transactions may require supplementary authentication, or that unusual transactions or access claims may trigger direct oversight or adaptive authentication requirements.

Simple user authentication, simple web server authentication, simple client-side SSL, basic PKI, is no longer enough when malware is now usually the sophisticated product of a criminal enterprise. Forensic audit logs have never been more important. The good news is that -- thanks to concerns raised by outspoken techies like Hadmut Danisch -- there is public debate and significant developments in all these areas, and solutions (probably imperfect, but better) are on the horizon.

Suerte, 
       _Vin

PS. I have been a consultant to RSA for nearly 20 years and my bias is overt. I beg the indulgence of the List for the length of my comments.

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