Moti Yung and Adam Young on Kleptography and Cryptovirology 5: Skeptical Experts and Smart Attackers

Moti Yung now outlines how the expert community and antivirus industry reacted to his and Adam Young’s book, and dwells on the applied aspects of kleptography.

Reactions to “Malicious Cryptography – Exposing Cryptovirology” Book

Reaction to Young and Yung’s book

Reaction to Young and Yung’s book

We got some reaction to what we described in our book. It’s good to see the reaction. I told you before that the book came out in 2004, so here is a reaction from a famous virus book writer himself who decided to write a critique of the book (see image). Since I wrote a virus book, I will never write critiques of other people who write virus books, because for me it’s a conflict of interest. Ok, but let’s see what this fellow wrote.

He wrote: “Is the volume supposed to be a serious warning against new forms of malware? …” So, he’s doubting the goal of this book. And then he says: “In addition, much of the material concentrates on building more malign malware, rather than dealing with defense against it.” So, he noticed that we really wanted to have fun – good. And then, instead of criticizing us, he’s criticizing the community of virus writers. He says: “I’m not too worried about vxers (virus writers) getting ideas from Young and Yung: implementing crypto properly is a painstaking task, and from almost twenty years experience of studying blackhat products and authors, I’m fairly sure there’d be lots of bugs in what might be released.” Ok, so he doesn’t criticize us, he criticizes the virus writers, hackers, because they don’t know crypto, whatever; ok, good, fair enough.

Criticism is good, inaction is bad

Criticism is good, inaction is bad

Some director in some funding agency told us: “We do not consider these attacks as high priority or immediate.” And then we had reactions to the reactions (see left-hand image). I pointed out to some people that what we do is kind of a very cheap way to do denial-of-service using this power of asymmetric, public-key cryptography. Adam took the criticism a little bit more seriously and he said: “Wow, who needs to know cryptography?” So, he implemented a version of the active attack, this ransomware virus employing CAPI – Microsoft’s cryptographic API – to verify that you don’t really need to know cryptography, you just call the API: you have to know the verb Encrypt, you have to know the word Random – good.

Around 2007, strong ransomware employing public-key cryptography started to appear.

I told him not to worry about such things and not to worry about criticism: criticism is healthy and challenging, and that’s fine. And I told him that the only thing that really worries me is we suggested obvious countermeasures: extensive backup and recognizing crypto operation where it doesn’t belong, and I was worried that the antivirus forces, those that claim to do antivirus, don’t pick on it. I don’t see them getting ready to what we pointed out. So, as a result we had some other ideas and we didn’t even bother to publish them in this direction.

The bad guys picking up cryptovirological ideas to launch ransomware

The bad guys picking up cryptovirological ideas to launch ransomware

And then, around 2007, strong ransomware employing public-key cryptography started to appear. So, virus spreading started using botnets, which is very similar to the password snatching channel where you don’t know who the attacker is, and ransomware that asks you for money. So, the conclusion is: the bad guys’ business is to try to make money, and they ignore recommendations from heads of funding agencies and book writers that write criticism of other books. Simply, they want to make money. And, of course, there are various discussions about whether these attacks are severe, important, what they are, how serious they are, whether there are alternative attacks. I’m not getting into this; I’m just pointing out what we did and what was done, and you’ll be the judge.

Dissecting the Kleptography Side of the Coin

Reverse side of cryptovirology

Reverse side of cryptovirology

So, this is the current state of affairs regarding these cryptovirological attacks. Then we kind of abandoned writing about cryptoviruses and concentrated more, and still concentrating, on something that we call kleptography. It’s a play on words: it’s a combination of cryptography and klepto, which is theft.

So, we noticed that in those malware designs we always have kind of a crypto Trojan horse, core, that was doing cryptographic war, and then there was a spread mechanism that was a virus replicating through the system to get access. At some point of the investigation, and we don’t remember when, how and who, we raised the question: what if the crypto Trojan that does the crypto work, instead of putting it in a virus, put it inside the cryptosystem?

Simmons observed already in the 1970s that certain ciphertext and public key values have redundant information in them, and they can carry information that was not intended. So, we said: “Aha, maybe.” The thing we tried to investigate is: if a cryptosystem is in tamper-proof hardware, which people thought to be the most trusted way to implement cryptosystem at the time, then no one knows what algorithm runs there.

So, the manufacturer of such highly trusted tamper-proof hardware, instead of putting the benign cryptosystem, the RSA cryptosystem, can put the Trojan cryptosystem. And I’m very worried nowadays when people talk about trusted computing modules, and some of them have certain tamper-proof properties. And I’m also worried about open source code, that even though it’s open source, nobody reads it. With open source, when it’s cryptography, read it! It should be open window source, not just open source that everybody ignores.

The fundamental idea is that there are ways to implement cryptography in a way that looks to everybody like it is doing the right thing, but not necessarily so.

First step in experimenting with kleptography

First step in experimenting with kleptography

So, what we did as the first step is we generated the crypto Trojan that runs RSA key generation that randomly generates composite numbers N, which is really a multiple of two strong primes p*q (see image). It uses real randomness, it’s not monkeying with weak generator and things like this, it’s really strong. It looks random to everybody, and it is secure, so it has first proof of security; this is as good as any other RSA key that you generate. I’m talking just about composing.

But the Trojan’s creator has a trapdoor that from N itself, namely the bits of N, looks at N, and it has an algorithm to read the factorization of N, read the inside N. Any other reverse engineer cannot factor – yes, we can’t, right? The attack is exclusive, and here you need the second security proof: security of the attacker, exclusivity of the attacker. So, the bottom line is you have to trust the producer of the tamper-proof hardware or the producer of the software, if you don’t look at the software, not just the fact that the device looks good. Keep the bottom line in mind. I’m not going to cover this, it requires another talk, but keeps the moral of the story.

Read previous: Moti Yung and Adam Young on Kleptography and Cryptovirology 4: Password Snatching and Secure Info Stealing

Read next: Moti Yung and Adam Young on Kleptography and Cryptovirology 6: The Summary

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