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The point about trusting hosting providers is an interesting one. Indeed, when renting a Virtual Private Server from a service provider, you have no choice but

The point about trusting hosting providers is an interesting one. Indeed, when renting a Virtual Private Server from a service provider, you have no choice but to trust them to keep your data safe. This made we wonder: would it be possible to actually secure the server in such a manner that the hosting party won't have access to your stuff without your say so ? I think you can (sort of) do this already with having something like an encrypted virtual server running on the rented VPS. Of course, I don't think this is bullet-proof and you also do have the downside of an additional layer of overhead that comes from further virtualization of your actual server(s).

etherael 13y ago
I have a dedicated server with encrypted partitions and admin backdoors turned off at ovh. So theoretically they shouldn't be able to access the running system, and if they take it down to access the partitions directly, they're encrypted so that won't work either.
- dualboot 13y ago
  The right answer. With a design that focuses on simplicity ( reducing the entry points ) you can be pretty well assured that if someone attempts to gain access to your data you will likely know. For me that is an important factor. I rather dislike the fact that in scenarios like Gmail and other providers of their ilk -- access is provided transparently to a third party. Running your own server can give you a reasonable expectation of privacy. Even in a hosted/colocated environment if you take the time and effort.
  - etherael 13y ago
    That said, even with a dedicated server, I still use gmail, because https://github.com/etherael/phoneme https://github.com/etherael/phoneme
- Sami_Lehtinen 13y ago
  That's why they take memory snapshot first, which is trivial with VPS and then pick encryption keys from it to access encrypted volumes. This is well known method and works with pure hardware machines too with physical access. It's great question when you get to server, to shut it down or leave on. If on, it could destroy data, if turned off encryption keys are gone. I think it would require some individual case analysis before deciding which one is better approach.
  - etherael 13y ago
    Isn't the pure hardware method for memory snapshots some ridiculously complex mechanism with freezing the memory and quickly transferring it to a reading device? If you're going to pull this, you need to know in advance that it's necessary, that's not some minor thing that everyone is going to just do automatically, it's an extra, complicated step it's easy to screw up. That said, I acknowledge the possibility of compromise in the aforementioned scenario, but once again I don't understand people who always jump to the "I am vulnerable to this narrow threat model, ergo, I should not bother to protect myself against any threat models". Especially when the measures you can take to protect yourself most likely will address the actual threat models you are liable to encounter.
    - lloeki 13y ago
      > Isn't the pure hardware method for memory snapshots some ridiculously complex mechanism with freezing the memory and quickly transferring it to a reading device? With Virtual Private Servers, it's trivial to do the virtualized version of this through the hypervisor.
      - etherael 13y ago
        My original statement said "dedicated server". The response said; "virtual server attack, also works with pure hardware machines". The only version of this attack that is relevant to the original statement is one that works on a dedicated server, so re-stating that it's trivial to do this against a virtual private server isn't really adding anything to the conversation.
- bigiain 13y ago
  Possibly some too-cynical questions… Do you think ovh is any less beholden to GCHQ than Google et al are to the NSA? Do you think your encrypted partitions and turned-off admin backdoors protect you much against people with physical access to the hardware?
  - etherael 13y ago
    > Do you think ovh is any less beholden to GCHQ than Google et al are to the NSA? OVH maybe a little more, because at least they're not under the direct auspice of the most megalomaniacal state in the world and will act according to their economic incentives in being a reliable and trustworthy service provider, which in a purely free market would align their interests with my own. However being as they are subject to various hostile state entities that have the ability to exert deleterious effects on that self interest, to the extent that they are forced to, they will cooperate with those entities. I take action to protect myself from those threats to the greatest extent that I am able in either scenario whilst acknowledging that every theoretical threat model can never be entirely negated, coupled with the fact that at the end of the day, bothering to break through all of my measures and taking that trouble, they would find basically nothing that they were interested in. I despise the state, sure, I'd like to see it dissolve into something like the system outlined in the machinery of freedom, sure. However in my view, taking any violent measures to expedite this process would both make me as bad as the enemy, and compromise the goal of a better world even if it actually contributed to the downfall of the state. > Do you think your encrypted partitions and turned-off admin backdoors protect you much against people with physical access to the hardware? "Much" more than non encrypted partitions and not turned off admin backdoors? Absolutely. Completely and utterly impenetrable to any attack by any means at all? Not likely, I can think of one off the top of my head that would work; freeze the memory, get an image, power off the system and extract the encryption keys from the image to re-mount the partitions. That's 1) not automatic 2) not easy 3) easy to screw up 4) not undetected
    - bigiain 13y ago
      Great response - thanks. Another question - have you done the thinking or got some advice about whether marginally trusting a potentially subvert-able hosting company in a jurisdiction you don't particularly trust (US, UK, and unfortunately for me, Australia) is likely to be a better or worse bet than trying to source a server/vps in a more trusted jurisdiction? (perhaps Iceland? Or am I fooling myself assuming there's anywhere "trustworthy"?)
- oijaf888 13y ago
  How do you handle reboots? If all of your partitions are encrypted I would guess you use a serial console to enter in the encryption password to decrypt and mount the actual OS drive?
  - etherael 13y ago
    small boot partition (basically enough to boot, get network, start ssh), all the actual data and /tmp on encrypted stores.
    - th0br0 13y ago
      But do you validate that boot partition each time you reboot the system? How do you know that your computed hashsum (or similar) is actually the true one? ...
      - etherael 13y ago
        got a hash of the boot partition, validate when it comes back up.
        e12e 13y ago
        How do you know that you're not logging in to a vm, with all the data mirrored from your physical server?
        etherael 13y ago
        This is reasonably clever, but how do you get a full disk mirror from a server you can't get into without powering off, if you do power off, the amount of time the system is down is a tipoff to the target as to what's going on. Assuming however it could somehow be pulled off; I guess potential ways to mitigate would be to keep a copy of the exact hardware characteristics of the system you originally have, kernel log on bootup, precise size of disks, chipsets of all the various controllers and compare when the system reboots. It would however be possible though extremely hard to get an exact duplicate of all of these at the virtualisation layer level. You could call the virtualisation layer in the cpu requesting access to virtualise a subsystem, clock the data bus speeds... There should be some overhead from virtualisation that wasn't there when dedicated... It's an interesting problem. I'll think more about it.
AnthonyMouse 13y ago
A good compromise is to just run the actual machine in your house and rent a VPS for the sole purpose of installing a VPN server to provide your machine at home with access to a static IP address that doesn't have outgoing SMTP blocked. That way all the VPS is doing is forwarding data to and from your machine at home and it doesn't have access to anything your ISP wouldn't, and TLS/PGP/etc. goes a long way to help with that as well. That should keep anyone from reading your email (assuming you and other senders are using TLS), but the next problem is that an ISP-level observer can always tell who you're corresponding with unless you use something like mix nets or Tor. And allowing that requires some cryptographic authentication method to distinguish legitimate anonymized senders from spammers without leaking the sender's identity to an intermediary. Having the sender sign the message and then encrypt the message, the signature and anything else that identifies the sender with the recipient's public key ought to do it but I'm not sure if there is any existing software that will actually do that. It might be possible using a combination of PGP to authenticate the sender and SMTP TLS over Tor to actually transmit the message, but the missing piece is for the sender authentication to be integrated with the spam filter.
clarkm 13y ago
No -- unless you have exclusive physical control of the machine you'll always be vulnerable. A malicious VPS provider has access to the machine's RAM, which means they can do almost anything. For example, they could extract your SSH private key and silently decrypt all your traffic. Is such an attack easy? No. But I could compile sshd with debug symbols and it would be. Even without them it's still possible, just very difficult. Though nothing a skilled employee of a nation-state couldn't do.
- e12e 13y ago
  As far as I know, SSH v2 offers perfect forward secrecy, so the attacker would have to read the session key from ram, not the private key (the private key would allow the attacker to do MITM, though).

etherael 13y ago

I have a dedicated server with encrypted partitions and admin backdoors turned off at ovh. So theoretically they shouldn't be able to access the running system, and if they take it down to access the partitions directly, they're encrypted so that won't work either.

dualboot 13y ago
The right answer. With a design that focuses on simplicity ( reducing the entry points ) you can be pretty well assured that if someone attempts to gain access to your data you will likely know. For me that is an important factor. I rather dislike the fact that in scenarios like Gmail and other providers of their ilk -- access is provided transparently to a third party. Running your own server can give you a reasonable expectation of privacy. Even in a hosted/colocated environment if you take the time and effort.
- etherael 13y ago
  That said, even with a dedicated server, I still use gmail, because https://github.com/etherael/phoneme https://github.com/etherael/phoneme
Sami_Lehtinen 13y ago
That's why they take memory snapshot first, which is trivial with VPS and then pick encryption keys from it to access encrypted volumes. This is well known method and works with pure hardware machines too with physical access. It's great question when you get to server, to shut it down or leave on. If on, it could destroy data, if turned off encryption keys are gone. I think it would require some individual case analysis before deciding which one is better approach.
- etherael 13y ago
  Isn't the pure hardware method for memory snapshots some ridiculously complex mechanism with freezing the memory and quickly transferring it to a reading device? If you're going to pull this, you need to know in advance that it's necessary, that's not some minor thing that everyone is going to just do automatically, it's an extra, complicated step it's easy to screw up. That said, I acknowledge the possibility of compromise in the aforementioned scenario, but once again I don't understand people who always jump to the "I am vulnerable to this narrow threat model, ergo, I should not bother to protect myself against any threat models". Especially when the measures you can take to protect yourself most likely will address the actual threat models you are liable to encounter.
  - lloeki 13y ago
    > Isn't the pure hardware method for memory snapshots some ridiculously complex mechanism with freezing the memory and quickly transferring it to a reading device? With Virtual Private Servers, it's trivial to do the virtualized version of this through the hypervisor.
    - etherael 13y ago
      My original statement said "dedicated server". The response said; "virtual server attack, also works with pure hardware machines". The only version of this attack that is relevant to the original statement is one that works on a dedicated server, so re-stating that it's trivial to do this against a virtual private server isn't really adding anything to the conversation.
bigiain 13y ago
Possibly some too-cynical questions… Do you think ovh is any less beholden to GCHQ than Google et al are to the NSA? Do you think your encrypted partitions and turned-off admin backdoors protect you much against people with physical access to the hardware?
- etherael 13y ago
  > Do you think ovh is any less beholden to GCHQ than Google et al are to the NSA? OVH maybe a little more, because at least they're not under the direct auspice of the most megalomaniacal state in the world and will act according to their economic incentives in being a reliable and trustworthy service provider, which in a purely free market would align their interests with my own. However being as they are subject to various hostile state entities that have the ability to exert deleterious effects on that self interest, to the extent that they are forced to, they will cooperate with those entities. I take action to protect myself from those threats to the greatest extent that I am able in either scenario whilst acknowledging that every theoretical threat model can never be entirely negated, coupled with the fact that at the end of the day, bothering to break through all of my measures and taking that trouble, they would find basically nothing that they were interested in. I despise the state, sure, I'd like to see it dissolve into something like the system outlined in the machinery of freedom, sure. However in my view, taking any violent measures to expedite this process would both make me as bad as the enemy, and compromise the goal of a better world even if it actually contributed to the downfall of the state. > Do you think your encrypted partitions and turned-off admin backdoors protect you much against people with physical access to the hardware? "Much" more than non encrypted partitions and not turned off admin backdoors? Absolutely. Completely and utterly impenetrable to any attack by any means at all? Not likely, I can think of one off the top of my head that would work; freeze the memory, get an image, power off the system and extract the encryption keys from the image to re-mount the partitions. That's 1) not automatic 2) not easy 3) easy to screw up 4) not undetected
  - bigiain 13y ago
    Great response - thanks. Another question - have you done the thinking or got some advice about whether marginally trusting a potentially subvert-able hosting company in a jurisdiction you don't particularly trust (US, UK, and unfortunately for me, Australia) is likely to be a better or worse bet than trying to source a server/vps in a more trusted jurisdiction? (perhaps Iceland? Or am I fooling myself assuming there's anywhere "trustworthy"?)
oijaf888 13y ago
How do you handle reboots? If all of your partitions are encrypted I would guess you use a serial console to enter in the encryption password to decrypt and mount the actual OS drive?
- etherael 13y ago
  small boot partition (basically enough to boot, get network, start ssh), all the actual data and /tmp on encrypted stores.
  - th0br0 13y ago
    But do you validate that boot partition each time you reboot the system? How do you know that your computed hashsum (or similar) is actually the true one? ...
    - etherael 13y ago
      got a hash of the boot partition, validate when it comes back up.
      - e12e 13y ago
        How do you know that you're not logging in to a vm, with all the data mirrored from your physical server?
        etherael 13y ago
        This is reasonably clever, but how do you get a full disk mirror from a server you can't get into without powering off, if you do power off, the amount of time the system is down is a tipoff to the target as to what's going on. Assuming however it could somehow be pulled off; I guess potential ways to mitigate would be to keep a copy of the exact hardware characteristics of the system you originally have, kernel log on bootup, precise size of disks, chipsets of all the various controllers and compare when the system reboots. It would however be possible though extremely hard to get an exact duplicate of all of these at the virtualisation layer level. You could call the virtualisation layer in the cpu requesting access to virtualise a subsystem, clock the data bus speeds... There should be some overhead from virtualisation that wasn't there when dedicated... It's an interesting problem. I'll think more about it.

AnthonyMouse 13y ago

A good compromise is to just run the actual machine in your house and rent a VPS for the sole purpose of installing a VPN server to provide your machine at home with access to a static IP address that doesn't have outgoing SMTP blocked. That way all the VPS is doing is forwarding data to and from your machine at home and it doesn't have access to anything your ISP wouldn't, and TLS/PGP/etc. goes a long way to help with that as well. That should keep anyone from reading your email (assuming you and other senders are using TLS), but the next problem is that an ISP-level observer can always tell who you're corresponding with unless you use something like mix nets or Tor. And allowing that requires some cryptographic authentication method to distinguish legitimate anonymized senders from spammers without leaking the sender's identity to an intermediary. Having the sender sign the message and then encrypt the message, the signature and anything else that identifies the sender with the recipient's public key ought to do it but I'm not sure if there is any existing software that will actually do that. It might be possible using a combination of PGP to authenticate the sender and SMTP TLS over Tor to actually transmit the message, but the missing piece is for the sender authentication to be integrated with the spam filter.

clarkm 13y ago

No -- unless you have exclusive physical control of the machine you'll always be vulnerable. A malicious VPS provider has access to the machine's RAM, which means they can do almost anything. For example, they could extract your SSH private key and silently decrypt all your traffic. Is such an attack easy? No. But I could compile sshd with debug symbols and it would be. Even without them it's still possible, just very difficult. Though nothing a skilled employee of a nation-state couldn't do.

e12e 13y ago
As far as I know, SSH v2 offers perfect forward secrecy, so the attacker would have to read the session key from ram, not the private key (the private key would allow the attacker to do MITM, though).