SSL Considered Harmful

A page on my various security writings.

Each of the controversial issues raised herein is an advanced attack on a security system. Still, each is written for accessibility in mind - any developer or manager within the general rubric of security should be able to follow along. If not, please complain!

"the survival value of intelligence is that it allows us to extinct a bad idea, before the idea extincts us"

or, alternate translation:

"The scientist can annihilate his theory by his critique, without perishing along with it. In science, we let our hypotheses die in our stead."
Karl Popper [1]

Originally, this was a collection of rants designed to reverse-engineer SSL, certificates and the wider system of secure browsing. The mission has somewhat migrated to a more general one of improving our understanding of security systems (both mine and anyone else who wants to read as well).

But, please note: When I first started this debate, it was just a bit of fun, a way for a security guy to look at a system afresh, and stretch the mental muscles. Since then, however, phishing and the rest emerged as serious Internet fraud, and provided a benchmark and a reality to security that wasn't there earlier. It all became very serious.

Hard Truths about the Hard Business of finding Hard Random Numbers

AS many have noticed, there is now a permathread (Paul's term) on how to do random numbers. It's always been warm. Now the arguments are on solid simmer, raging on half a dozen cryptogroups, all thanks to the NSA and their infamous breach of NIST, American industry, mom's apple pie and the privacy of all things from Sunday school to Angry Birds.

Yet we've come to a point I believe where we do know enough. This is my attempt to establish a minimum practice for building RNGs, in 12 points.

Originally posted on FC, the updated copy now lives here. Read on for the Hard Truths about the Hard Business of finding Hard Random Numbers...

Why the NSA loves the one-security-model HTTPS fanaticism of the Internet

OF all the things I have written about the traps in the HTTPS model for security, this one diagram lays it out so well, I'm left in the dirt. ...

Read on for Why the NSA loves HTTPS...

History of Risks & Threat Events to CAs and PKI

IN Risk Management terms, History refers to the series of attack events that are documented and examinable, for the purpose of validating threat attack models.

This is an ongoing effort to document those events that have been reasonably seen as attacks and threats relevant to the CA and the usage of certificates. The purpose of this page is to help risk assessments validate their threat models against recorded events.

Read on for History of Risks & Threat Events...

The Curse of Cryptographic Numerology

The problem of cryptographic numerology has plagued modern cryptography throughout most of its life. The basic concept is that as long as your encryption keys are at least "this big," you're fine, even if none of the surrounding infrastructure benefits from that size or even works at all. The application of cryptographic numerology conveniently directs attention from the difficult to the trivial, because choosing a key size is fantastically easy, whereas making the crypto work effectively is really hard.

Read on for the Curse of Cryptographic Numerology...

What makes a Security Project?

This is a (three years) old essay in which I looked at as many projects as I knew at the time, and compared them. Out of the comparison, I developed a list of 20 simple measures or binary metrics with which to rate them.

Mapped as a matrix and totalled up for top scorers, the ideas may be useful for others to read. It might also be amusing; the lowest scorer of all is my all time favourite crypto application. Note the work is unfinished and not something I suggest you rely on. I offer it more as a source of debate and usefulness to others, and please excuse the bountiful errors. Adverse and other comments on the blog, please!

Hypotheses in Secure Protocol Design

How to create a secure protocol? Or a secure product of any description? It's a vexing question, and many have broken their spirits on it. Over time, threads and rhymes emerge, and these I've collected into a series of hypotheses.

I am slowly introducing them over on the blog, as some topical news develops to introduce the point. So far, I've got as far as H3 and H6:

H1 -- The One True Cipher Suite
H2 -- Divide and Conquer
H3 -- There is only Mode, and it is Secure
H4 -- The First Requirement of Security is Usability
H5 -- Security Begins at the Application and Ends at the Mind.
H6 -- It's your job. Do it!

White Helicoptor
Is eavesdropping a "Clear and Present Danger"
the definition of a validated threat?

In which I define a validated threat as one which is a Clear and Present Danger. Compared and contrasted with the emerging threat of eavesdropping, I conclude that it is Present and a Danger, but is not yet Clear.

Reliable Connections are Not

Perhaps better entitled "On the limits of reliability in connections." This is a rant that documents the specific corner cases that make connections "mostly reliable."

For the most part, most software engineering does not need to worry about these nitpicking details. Connections are reliable enough, they are "good enough for government work" as the saying goes. But for those few applications that require real reliability - finance, payments, medical, weapons, robotics, transport, etc etc - something else is needed. (Well, maybe that isn't such a short list after all?)

This essay lays the groundwork for that something else. That might come later, in time. If you really truly require it though, you can always reliably pay for it :) (Comments can go here.)

Voice Threat Models are Snafu

A recent spate of reports on VoIP and cryptophones has called for more encryption. I fear that we've bungled the threat model yet again - in exactly the same way as with SSL.

Cryptography is the art of using mathematics to protect things that we know we can protect with mathematics; unfortunately the desire to throw bucketloads of cipher bits at the problem has missed the fact that by far the biggest risk to users of phones is *tracking*.

(More: -2 -1 1 2. )

Security Revisionism

Not really a rant, but an article for JIBC that assumes security is failed, and surveys open areas of research to help:

Abstract. Security isn't working, and some of us are turning to economics to address why this is so. Agency theory casts light on cases such as Choicepoint and Lopez . An economics approach also sheds light on what security really is, and social scientists may be able to help us build it. Institutional economics suggests that the very lack of information may lead to results that only appear to speak of security.

The State of the Net - 2006
Rant out the Old, rant in the New!

Another year has passed, and what was the big news? 2005 was .... The Year I Lost My Identity. 2006 I christened as The Year of the Bull with a fine representation from Daniel Kozan.

GP4.3: Case Study #3 - Phishing

As an outgrowth of a rant or essay on the economic interactions of fraud and security in new business models, I wrote a case study on Phishing. For the most part, the value of this case study is the listing of Forces imposing on SSL's development around 1994-95. This approach draws from Porter's Five Forces approach to institutions. It's a fun list, even if it has roots back into b-speak.

The wider point I'm making in that case study is that the SSL and certificates system was put in too early, before GP. To see what that means, you'd have to read through the three core sections:

The wider concept of when to put the security system in came out of many analysies, including that of SSL as presented in these rants. It's probably worth mentioning that we made the same mistake with Ricardo. The key observation drawn from these experiences was that security that came in late seemed to work better than security that came in early - why was that? That's what the rant tries to answer.

Security Usability (PDF only)

The security industry's desire for no-risk security has resulted in less security overall. Frankly, if people don't use it, it doesn't deliver any security whatsoever, so usability has to come first.

I'm not so sure what's so hard to get about this concept, but security experts continue to suck air in between the teeth when they hear of encrypted email without proper certificates or VoIP applications without Guild-approved cryptosystems. So this battle has only just begun it seems.

The article was co-written with Peter Gutmann for the Crypto Corner of IEEE's Security & Privacy magazine (and is copyright by them). It also marks my first serious use of wikis which in itself was quite enlightening.

what it is and how it will eventually be dealt with

When JIBC asked me after a 9 year absence to write a 2 pager on the one subject that is more important than any other, it took no more than nano-seconds to leap onto my hobby horse - Phishing!

In two pages I could do no more than present an overview for business and financial executives. As a summary of my thoughts as to the state of the art in how to address phishing, it's pretty good.

Where it stops short of course is doing the work. That issue is the subject of future rants and articles, as these days there is more interest in the meta-topic of security practice than phishing per se.

"For a successful technology, reality must take precedence over public relations, for nature cannot be fooled."
Richard Feynman [2]

A Blackbird Moment
Microsoft confirms phishing is an attack on the browser

The crusade over browsers and phishing has become an underground legend that nobody dares name. Yet, when security professionals hear the name, they know the site! Infamy carries its costs though - both to my own reputation and to the reputation of browsing itself.

So it was with some degree of personal relief that we now have, as an industry, focussed the browser manufacturers on the goal. Phishing is an attack on the browser, and there is no longer a need for us to discuss that.

Thanks, Bill.

The Goal of Security

(Security Signalling - III)

Adam's insightful question on 'security signals' caused create ponderment. It's a really tough one. One thing that stuck in my mind was that FreeBSD and OpenBSD are secure. The rest? Don't know.

So why are these two, and presumably other BSD variants like BSDI and NetBSD, so stuck in the mind as 'secure' ? What's the signal? Here's one answer - these two operating systems practice the Goal of Security. It is partly in their writings but more importantly it is in their actions.

This essay attempts to lay out what it means to subscribe to Security as a Goal. It is nominally aimed at another project, Mozilla, which is rapidly approaching a test of its maturity and security. As it grows without apparent limit, it seems destined to enter that love-it-hate-it area where the user base is too big for attackers to ignore.

Mozilla may well claim to be passionate about security, but those are just words. In actions, Mozilla have had it easy; no real attacks in living memory (Shmoo was not an attack but an exploit), unlike the BSDs which have had to take the brunt of hacking attacks since the dawn of time. Time to get some security into the blood.

Netcraft breaks ranks and points the crooked black claw of doom at the SSL security model

The debate on SSL's security model just gets better and better. Now Netcraft have turned the whole model on its head, and created a browser plugin (for IE only unfortunately) that does the security thing by reference to a centralised database.

Who'd a thunk it?

User education: worse than useless

I didn't realise it at first, but this was a question that seriously needed an answer. Just why is it that we've spent the last decade giving the user good advice - the padlock protects you, beware of 40 bit crypto, or don't click on that email link - and we're still in this security mess?

"I think the subject which will be of most importance politically is Mass Psychology... Its importance has been enormously increased by the growth of modern methods of propaganda... Although this science will be diligently studied, it will be rigidly confined to the governing class. The populace will not be allowed to know how its convictions were generated." ---Bertrand Russell

As with most complex things, the answer is so simple we probably walked right past it: the users don't pay attention to education, and for quite good reasons. Which results that more user education is dangerous, as it avoids facing up to the real problem.

The State of the Net - 2005
in several rants around our new year of 2005, leading to the future, year by year...

Yes, it's been more than a year now, and little progress has been made. Other than by phishers, that is, so I christened 2004 as The Year of the Phish. Of course, we all knew that, so the more interesting future is in 2005, which I have christened as The Year of the Snail. Under pressure, and deprived of caffeine, I also wrote 2006, and beyond... but I wasn't able to christen that far ahead. Still, the Year of the Dogs is one contender, as I predict finally in Identity Theft: Why Hollywood has to take one for the team.

Sucking on the Lemon

(Security Signalling - I)

Adam Shostack pointed out how signalling is a lemon in its own right in the security industry, which got me thinking. Here's my proposal for a good signal: report all your crack attempts on a daily basis, and watch what happens when you actually get hacked. Just like sucking on a lemon, this will reveal to the market how secure your stuff is, whatever you do with the lemon that suddenly went sour!

The Market for Lemmings

(Security Signalling - II)

Again following Adam's lead, I've added an effort to define some characteristics of the security market. In brief: the security product is one that defies testing. I'm not sure that this is a new observation, but we have to start by documenting what we do know...

VeriSign's conflict of interest creates new threat

VeriSign are the market dominating seller of CA-signed certificates to help you in "secure ecommerce." What is less well known is that they are also a leading facilitator of "lawful interception and subpoena requests" services to Law Enforcement Agencies, ISPs and telcos!

Can you say conflict of interest ??

New Attack on Secure Browsing

Just when you thought it was safe to get back into browsing... I stumbled across this new way of futzing with people's minds. This page is now protected - see the secured by favicon-SSL padlock up on the top left of the URL bar.

Microsoft Internet Explorer users - secure browsing is not available to you as your browser is full of spyware, trojans and other malware. You should download and install Firefox this instant ! ! ! Alternatively, you can get more placebo security by adding this page as a Favourite, and then you will see what this attack is all about.

Making VeriSign like CocaCola
How CA Branding works against Phishing, substitute CA attack, etc etc

I've been proposing the branding box for some time now, but for some reason, this powerful idea to solve one of the great MITM attacks on SSL secure browsing hasn't gained traction. Here's an explanation of how branding can segment the MITM into 4 spaces, and clearly designate who is responsible for protection in that space.

The really exciting news is that Amir and Ahmad are actually building this into Mozilla.

What we do in the security world is we pick a system, and we tear it apart. It's a way of preparing to build the next system, and it's also fun. It has been known for a long time that secure browsing was only secure by dictat, but it didn't really matter as nobody ever got hurt. Ideal system to pick apart, and that's what this page is about. Since then, however, phishing has arisen as perhaps the first serious fraud that is totally Internet only. My best estimate of losses so far - a number that is very hard to quantify - is about one billion dollars.

"Science is the best defense against believing what we want to."
Ian Stewart [3]

Hence, my next rant:

Question on the state of the security industry

Phishing has become very serious. What is equally serious is that the Internet security community that put secure browsing in place back in 1994-1995 is ignoring it, all the while as the maelstrom grows around it. Meanwhile, there are consortia being formed, headlines being written, politicians bailing in, and identity theft is now the number one US consumer problem. Still ... nothing.

What's going on?

Who are you?

(WYTM revisited)

In contrast to the below, here is a rant that argues that WYTM may not be an appropriate question for a system like secure browsing. Although argued for email, the analogy holds: If we can't identify who the users are, adequately, then we can't identify their threats. Oops! Yet more evidence that Mallory was misrepresented as a threat...

Dr. Self-signed
How CAs Learned to Stop Worrying and Love the Cert?

Why is the market for certs so moribund? Well, one reason is that it lacks discrimination - a critical component as all marketeers know. This essential ingredient can be added easily with a dose of self-signed certificates and servers that help you to SSL protection. And, CAs stand to reap the benefits, as do users.

What's your threat model?

The threat model is perhaps the most important question in cryptography. Yet, in the case of SSL and secure browsing, the question was bungled. The threat model is not only wrong, in principle and in practice, it has nothing to do with the original requirements.

The Maginot Web

The CA-signed certificate protects against the spoof attack on users with all the pomp and circumstance of the Maginot Line. Huge cost, impeccable theory, and bypassed in the event.

Who's Afraid of Mallory Wolf?

The dreaded bogey-man has us all afeared, yet, he remains elusive, fleeting, and like all childhood nightmares, of exaggerated importance.

Now in Russian! Thanks to Dani for pointing that out.

How effective is open source crypto?

Extraordinarily so, but the opportunity has been lost.

Yes, these are all rants. Or, at their best, essays on the lamentable state of SSL security implementations. It's a complex subject, and I've been annoyed at certs ever since some salesman from Cybercash tried to convince me that I needed them, but couldn't say why.

The "need" for certs - in terms of the way the browsers force sites to deploy expensive, useless CA-signed certificates - is still with us. This page seeks to show that this is a gross failure of security engineering within the networking world.

But, to do so with yet another boring security paper, presented at yet another annual conference with too many acronyms, seems fruitless. Perhaps a more light hearted approach will reach out? Who knows, you tell me!


Some of these rants were posted on the list, which has a majordomo subscription. Archives of the list are stored at Mail-Archive (earlier) and at Mail-Archive (later) with responses to some of them at:

More Serious Reading

For more serious reading, try these:

PKI considered harmful
is a list of issues that exist with the wider scheme of Public Key Infrastructures. It has always been an ongoing work-in-progress over a decade or so, although I've not discovered so many new issues to add in recent years. (PS-A4, PDF-A4.)

Browser Threat Model
is an attempt to document the browser threat model, from today's perspective of 2004. This was an merely a draft, thrashed out over a few nights back in 2004. Comments welcome! See the MindMap of the secure browsing attack model.

(Also see more recent work from 2009: Ivan Ristic' blogged on his efforts).

Financial Cryptography entries on Phishing
Since phishing arose to actually challenge the crypto systems and rip money out of people's online accounts, I've written quite a lot in more serious forum: the FC blog. Click on above to see the searched list.

For Actual Solutions to Phishing

This page is not about actual solutions to Phishing, but how to solve the underlying bugs that caused phishing. For solutions to Phishing itself, you are better off dropping in to the anti-fraud coffee room. That being said, here is a list of early research and experiments in solutions, especially those that have passed our hypercritical seal of approval. Curiously, the industry once again moved past the security aspects of these solutions without noticing, an observation that led to my thoughts in The Market in Silver Bullets.

The first and possible most comprehensive approach was Trustbar! It is a plugin browser toolbar that displays the CA's logo and name, and the domain name of the site. It also gives the user the ability to label each site with different personalised labels.

Even simpler yet! Based on the fundamental concepts of petnames and Zooko's Triangle the Petnames toolbar does one small thing and does it well: it encourages the user to place a unique personalised label, or petname, on each important SSL site.

This approach tries to create images that the user knows but are never communicated, derived from a shared secret approach known as SRP. In some ways it is similar to Trustbar, in other ways different.


[1] The precise reference for this quote is unknown.

Florian Weimer writes: Your Popper quote is from a German broadcast program which is reprinted in "Alles Leben ist Problemlösen" (Piper 1994): "Die Amöbe flieht vor der Falsifikation: Ihre Erwartung ist ein Teil von ihr, und vorwissenschaftliche Träger werden oft durch die Widerlegung der Hypothese vernichtet. Einstein dagegen hat seine Hypothese objektiviert. Die Hypothese ist etwas außerhalb von ihm; und der Wissenschaftler kann seine Hypothese durch seine Kritik vernichten, ohne selbst mit ihr zugrunde zu gehen. In der Wissenschaft lassen wir unsere Hypothesen für uns sterben."
So it's more like "The scientist can annihilate his theory by his critique, without perishing along with it. In science, we let our hypotheses die in our stead." It's a bit distorted, but I still think it's the source of your aphorism (unless someone discovers a better one).

Twan van der Schoot suggests: Ref

[2] R.P. Feynman, Personal observations on the reliability of the Shuttle

[3] Ian Stewart, From What Does a Martian Look Like? The Science of Extraterrestrial Life