4 ms·

It's hilarious that it uses public-key crypto, yet lets the client know the private key. What's even the point, then?

soared 9y ago
I mean a technical user capable of this solution is not very likely to get hit by this in the first place. The hacker probably doesn't care if x% of people defeat the encryption.. as long as x% pay the ransom.
- kybernetikos 9y ago
  Given the infrastructure and health victims that have been hit, I certainly hope that some serious people are looking into this. Given the relatively small sums of money we've seen flowing into the bitcoin addresses, if I were the perpetrator, I would not think I'd got a particularly good deal - exchanging 40k or so for interest from a number of heavy hitting actors just doesn't seem worth it.
  - jamiek88 9y ago
    It probably does to a pair of 16 year olds in eastern Europe. The problem with these tools being made and leaked is it lowers the bar of technical expertise needed to run a scheme like this. If it still took massive knowledge and experience the likelihood is that person could earn more legitimately thus there is a smaller pool of potential attackers.
  - closeparen 9y ago
    If the infrastructure and health victims can be compromised by generic Windows hardware not even targeting them in particular & can't recover from backups, I'd argue they aren't heavy hitters. Though maybe they'll bring some in now.
deleted 9y ago
[deleted]
gregmac 9y ago
In the case of ransomware, it just has to work most of the time. If the WannaCrypt author(s) want to (partly) address this particular tool, they could, for example, just make it reboot on XP after encrypting everything.
kccqzy 9y ago
Exactly. I would've thought the malware would ask a C&C server to generate a key pair and then only send the public key to the malware. But I guess perhaps that required too much processing power for the server. But then again this can also distributed: let a random victim generate an RSA keypair for another victim.
- kybernetikos 9y ago
  If those network requests could be identified, the whole thing would be shut down by network operators.
  - derefr 9y ago
    Instances of the worm could notice they've landed on especially-low-activity systems with open ports, and then modify their own "descendants" to contact them on that host for key-generation. (And then relay the key material to the origin host, before wiping their local copy.) If the worm then notices that their host "goes active" (e.g. starts a login session), they could "submerge", closing the relevant ports and so forth, until the activity goes away; and their descendant instances would, while this is happening, fall back to the ancestor[N+1]th host.
- kaoD 9y ago
  This allows computers cut off from the internet to be infected too. Juicy and the risk is minimal.
  - paulddraper 9y ago
    Bitcoin payment requires internet.
    - brokenmachine 9y ago
      You don't need bitcoin payment to be infected.
ahomescu1 9y ago
I don't know the exact details of how WannaCry encrypts the files, but ransomware generally works like this: when hitting a new machine, it generates a random key K1 and then encrypts all the user's files with AES (or some other symmetric key encryption) using K1 as the key. It then encrypts K1 itself using some public key Kpub embedded in the ransomware, then stores the encrypted K1 on disk. When the user pays the ransom, they receive the corresponding private key Kpriv that allows them to decrypt K1, which then lets them decrypt all their files. I think what this tool does is read the unencrypted K1 directly from memory, which means Kpriv is no longer needed. EDIT: One correction: the user doesn't receive Kpriv, instead they send the encrypted K1 to the ransomware owner who decrypts it and sends back K1.
- CiPHPerCoder 9y ago
  There are 4+N keys involved. - The attacker's RSA private key (UNKNOWN) - The attacker's RSA public key (KNOWN) - The local device's RSA private key (KNOWN, but then poorly wiped) - This is encrypted with the attacker's RSA public key - The local device's RSA public key (KNOWN) - A separate AES key for each file - These are encrypted with the local device's RSA public key How decryption should work: Get the local device's RSA private key from the attacker (EDIT: this is not the attacker's RSA private key, it's the local one), then you can decrypt the AES key for each file.
  - uep 9y ago
    If someone were to pay up and receive the attacker's private key, what's to stop them from distributing it to others?
    - equivrel 9y ago
      That's exactly the trick: the attacker doesn't send you their private key, they decrypt (using their private key) the other private key that the ransomware generated on your machine, which is what was used to encrypt the per-file AES keys.

I mean a technical user capable of this solution is not very likely to get hit by this in the first place. The hacker probably doesn't care if x% of people defeat the encryption.. as long as x% pay the ransom.

kybernetikos 9y ago
Given the infrastructure and health victims that have been hit, I certainly hope that some serious people are looking into this. Given the relatively small sums of money we've seen flowing into the bitcoin addresses, if I were the perpetrator, I would not think I'd got a particularly good deal - exchanging 40k or so for interest from a number of heavy hitting actors just doesn't seem worth it.
- jamiek88 9y ago
  It probably does to a pair of 16 year olds in eastern Europe. The problem with these tools being made and leaked is it lowers the bar of technical expertise needed to run a scheme like this. If it still took massive knowledge and experience the likelihood is that person could earn more legitimately thus there is a smaller pool of potential attackers.
- closeparen 9y ago
  If the infrastructure and health victims can be compromised by generic Windows hardware not even targeting them in particular & can't recover from backups, I'd argue they aren't heavy hitters. Though maybe they'll bring some in now.

deleted 9y ago

[deleted]

gregmac 9y ago

In the case of ransomware, it just has to work most of the time. If the WannaCrypt author(s) want to (partly) address this particular tool, they could, for example, just make it reboot on XP after encrypting everything.

kccqzy 9y ago

Exactly. I would've thought the malware would ask a C&C server to generate a key pair and then only send the public key to the malware. But I guess perhaps that required too much processing power for the server. But then again this can also distributed: let a random victim generate an RSA keypair for another victim.

kybernetikos 9y ago
If those network requests could be identified, the whole thing would be shut down by network operators.
- derefr 9y ago
  Instances of the worm could notice they've landed on especially-low-activity systems with open ports, and then modify their own "descendants" to contact them on that host for key-generation. (And then relay the key material to the origin host, before wiping their local copy.) If the worm then notices that their host "goes active" (e.g. starts a login session), they could "submerge", closing the relevant ports and so forth, until the activity goes away; and their descendant instances would, while this is happening, fall back to the ancestor[N+1]th host.
kaoD 9y ago
This allows computers cut off from the internet to be infected too. Juicy and the risk is minimal.
- paulddraper 9y ago
  Bitcoin payment requires internet.
  - brokenmachine 9y ago
    You don't need bitcoin payment to be infected.

ahomescu1 9y ago

I don't know the exact details of how WannaCry encrypts the files, but ransomware generally works like this: when hitting a new machine, it generates a random key K1 and then encrypts all the user's files with AES (or some other symmetric key encryption) using K1 as the key. It then encrypts K1 itself using some public key Kpub embedded in the ransomware, then stores the encrypted K1 on disk. When the user pays the ransom, they receive the corresponding private key Kpriv that allows them to decrypt K1, which then lets them decrypt all their files. I think what this tool does is read the unencrypted K1 directly from memory, which means Kpriv is no longer needed. EDIT: One correction: the user doesn't receive Kpriv, instead they send the encrypted K1 to the ransomware owner who decrypts it and sends back K1.

CiPHPerCoder 9y ago
There are 4+N keys involved. - The attacker's RSA private key (UNKNOWN) - The attacker's RSA public key (KNOWN) - The local device's RSA private key (KNOWN, but then poorly wiped) - This is encrypted with the attacker's RSA public key - The local device's RSA public key (KNOWN) - A separate AES key for each file - These are encrypted with the local device's RSA public key How decryption should work: Get the local device's RSA private key from the attacker (EDIT: this is not the attacker's RSA private key, it's the local one), then you can decrypt the AES key for each file.
- uep 9y ago
  If someone were to pay up and receive the attacker's private key, what's to stop them from distributing it to others?
  - equivrel 9y ago
    That's exactly the trick: the attacker doesn't send you their private key, they decrypt (using their private key) the other private key that the ransomware generated on your machine, which is what was used to encrypt the per-file AES keys.