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WannaCry in-memory key recovery for Windows XP

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Re: WannaCry in-memory key recovery for Windows XP

#81

Post by kutkloon7 »

murbard2 wrote: post #47

The attackers seem to have a poor grasp on cryptography. The entire point of RSA is that they don't have to generate the key locally. Just ship your ransomware with the attacker's public key, generate a symmetric key K locally, encrypt the data with K, encrypt K with the public key, offer to decrypt K for a ransom. There seems to be an inverse correlation between smart and evil in human beings which is reassuring, bu…

What is the fundamental difference? The pitfall that makes it possible to decrypt is that the key which is needed to decrypt is not cleared from memory. Your proposed strategy has exactly the same problem.

What would work is hardcoding a large number of public keys in the binary. Then upon paying the ransom the attacker could give the private key to the victim.

Re: WannaCry in-memory key recovery for Windows XP

#82

Post by roblabla »

kutkloon7 wrote: post #81
murbard2 wrote: post #47

The attackers seem to have a poor grasp on cryptography. The entire point of RSA is that they don't have to generate the key locally. Just ship your ransomware with the attacker's public key, generate a symmetric key K locally, encrypt the data with K, encrypt K with the public key, offer to decrypt K for a ransom. There seems to be an inverse correlation between smart and evil in human beings which is reassuring, bu…

What is the fundamental difference? The pitfall that makes it possible to decrypt is that the key which is needed to decrypt is not cleared from memory. Your proposed strategy has exactly the same problem. What would work is hardcoding a large number of public keys in the binary. Then upon paying the ransom the attacker could give the private key to the victim.

That is not how async crypto works. If you only provide the public key (as opposed to creating a keypair locally) you could print it out to the victim and it wouldn't matter, as it can only be used to encrypt.

Re: WannaCry in-memory key recovery for Windows XP

#83

Post by [deleted] »

murbard2 wrote: post #47

The attackers seem to have a poor grasp on cryptography. The entire point of RSA is that they don't have to generate the key locally. Just ship your ransomware with the attacker's public key, generate a symmetric key K locally, encrypt the data with K, encrypt K with the public key, offer to decrypt K for a ransom. There seems to be an inverse correlation between smart and evil in human beings which is reassuring, bu…

[deleted]

Re: WannaCry in-memory key recovery for Windows XP

#84

Post by paupino_masano »

murbard2 wrote: post #47

The attackers seem to have a poor grasp on cryptography. The entire point of RSA is that they don't have to generate the key locally. Just ship your ransomware with the attacker's public key, generate a symmetric key K locally, encrypt the data with K, encrypt K with the public key, offer to decrypt K for a ransom. There seems to be an inverse correlation between smart and evil in human beings which is reassuring, bu…

Alas, in order to optimize profits you wouldn't want to use a shared key pair. The risk of course that once your private key is disclosed then you'll potentially thwart future revenue.

Re: WannaCry in-memory key recovery for Windows XP

#85

Post by kutkloon7 »

roblabla wrote: post #82
kutkloon7 wrote: post #81

Earlier quoted context omitted.

What is the fundamental difference? The pitfall that makes it possible to decrypt is that the key which is needed to decrypt is not cleared from memory. Your proposed strategy has exactly the same problem. What would work is hardcoding a large number of public keys in the binary. Then upon paying the ransom the attacker could give the private key to the victim.

That is not how async crypto works. If you only provide the public key (as opposed to creating a keypair locally) you could print it out to the victim and it wouldn't matter, as it can only be used to encrypt.

Which is exactly my point. Ideally, you want to encrypt with a key that is different from the key that you need to decrypt, so that you can encrypt without ever having the key that is needed to decrypt in memory. This is impossible with symmetric cryptography.

Re: WannaCry in-memory key recovery for Windows XP

#86

Post by nashashmi »

ezoe wrote: post #79
userbinator wrote: post #64

Earlier quoted context omitted.

I'm going to point at the elephant in the room and say that, there are probably quite a few reading this post and screaming in their mind, don't help them!! There seems to be an inverse correlation between smart and evil in human beings which is reassuring, but only mildly. Indeed, this isn't the first time ransomware with bad crypto has lead to a win for the good guys: http://blog.cassidiancybersecurity.com/post/201…

The knowledge he is writing is so basic anyone must understand. You're saying like "We should not teach programming publicly since bad guy may misuse the knowledge."

This is different. He I specifically addressing what the bad guys should do. If he talked in more technical terms without spelling out what the bad guys should do, your argument would be legitimate.

Re: WannaCry in-memory key recovery for Windows XP

#87

Post by e12e »

pmoleri wrote: post #59
tcbawo wrote: post #57

Earlier quoted context omitted.

Probably obvious, but they would not want to send a private key which could be used to help other victims. If they generated a symmetric key locally and encrypted it with their provided public key, they could decrypt the symmetric key for you in exchange for payment.

So, to check if I understood. The generated key is encrypted and the user has access to it. So, you send the encrypted key and pay the randsome to get the unecrypted private key. Is that so?

Almost, the last bit should read:

>... get The unencrypted secret symmetric (session/encryption) key

So ransomware ships with public key PubK, generates symmetric key K, encrypts user files - plaintext message M to get encrypted files, cipher text C:

K=128 random bits, generated on target system

C=aes(K, M)

Then the key K is encrypted with the public key PubK, yielding encrypted key, Ks. Finally K is deleted from memory/overwritten.

Ks can be decrypted by private key PrivK - known only to the author of the ransomware.

Now, the victim sends Ks and payment to the author/attacker.

The attacker decrypts Ks using PrivK, and gets K, which is sent back to the victim - who can presumably supply K to the ransomware. Ransomware then uses K to decrypt C, yielding M - the unencrypted files.

Re: WannaCry in-memory key recovery for Windows XP

#88

Post by ccvannorman »

canoebuilder wrote: post #75
Senderman wrote: post #68

Earlier quoted context omitted.

Not to interfere with any internal screaming, but I think (hope?) most would agree that a secondary elephant in the room is that suppressing knowledge so as not to help the "bad guys" tends to be the worse evil.

I don't see how that applies in this case. This is just someone saying hey bad guy, here is an idea on how to perform your dastardly act "better." Having this public doesn't really defend against it any way. And if someone were to perform this act, it would be easy enough to figure out what was going on.

I believe it applies, as someone who doesn't know much about crypto AND is interested in protecting myself, this small tidbit of information moves me closer to being an aware and self-defensive computer user.

Any bad guys with sufficient ambition and intelligence are going to get as far as they're going to get, and if you're afraid of talking in public because a "bad guy" might overhear you and become smarter, you really are living on the wrong side of matters.

Re: WannaCry in-memory key recovery for Windows XP

#89

Post by nthcolumn »

marksomnian wrote: post #39
nthcolumn wrote: post #37

Earlier quoted context omitted.

And Windows XP was not targeted at all by WannaCry.

In that case, Microsoft wouldn't have released an emergency patch for XP, three years after end of support. But they did [0]. [0]: https://blogs.technet.microsoft.com/msrc/2017/05/12/customer...

Come back to me when you find a single infection on XP with wcry 2.0, and then go look at when your 'emergency' patch was signed (Feb 17). Have you ever heard of 'PR'?

Re: WannaCry in-memory key recovery for Windows XP

#90

Post by paulddraper »

kutkloon7 wrote: post #85
roblabla wrote: post #82

Earlier quoted context omitted.

That is not how async crypto works. If you only provide the public key (as opposed to creating a keypair locally) you could print it out to the victim and it wouldn't matter, as it can only be used to encrypt.

Which is exactly my point. Ideally, you want to encrypt with a key that is different from the key that you need to decrypt, so that you can encrypt without ever having the key that is needed to decrypt in memory. This is impossible with symmetric cryptography.

You're right. On the other hand, asymetric encryption if a disk will be dog slow.
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