3 ms·

If someone has passive access to snoop, the odds they can perpetrate an active attack are so close to 100% as to make the distinction immaterial. Encryption wit

If someone has passive access to snoop, the odds they can perpetrate an active attack are so close to 100% as to make the distinction immaterial. Encryption without authentication accomplishes nothing. Worse, self-signed certificates train users to freely click through certificate warnings. People running servers with self-signed certificates are actively reducing what security we have available for the web. If we ever do get anything better than the existing CA structure, it won't do us any good if users have been trained to ignore browser security warnings anyway.

devinj 13y ago
Can you MITM public wifi? Real question, but I thought the answer was "no", which would make public wifi a compelling counter-example.
- nknighthb 13y ago
  I have no idea where you'd get the idea that the answer is "no". The answer is emphatically yes.
- syshax 13y ago
  Yes. You arp poison the default gateway and route traffic through your own host instead.
  - caf 13y ago
    Or spoof DNS responses to point to a machine under your control.
    - sp332 13y ago
      Or spoof a disassociation frame, then impersonate the access point so the victim connects to your computer instead.
antientropic 13y ago
I guess you don't agree with Poul-Henning Kamp in his FOSDEM keynote this year: https://www.youtube.com/watch?v=fwcl17Q0bpk https://www.youtube.com/watch?v=fwcl17Q0bpk (around 15:00) His claim is that browsers treating websites with self-signed certificates as less secure than non-encrypted websites by displaying big fat warnings is just about the greatest gift we can give to organisations like the NSA. It's not true that there is no material distinction between an active attack and passive eavesdropping. For the NSA to do active MITM attacks on all self-signed https traffic (in a world where all unencrypted http is replaced with self-signed https) would take massively more resources than passively monitoring unencrypted traffic. Plus the odds of them getting caught would be very high (since some people are going to notice that the certificate that shows up on the client is not what the server sent).
- nknighthb 13y ago
  PHK says many things I disagree with. You can't make browsers simply treat self-signed certificates the same as plain HTTP. You still have to warn the user that their desire for a secure connection (conveyed by their request to retrieve an https URL) cannot be fulfilled, and do so in a way that assures all users will notice before they do something like, say, type in their password. There is very little self-signed HTTPS traffic out there. The NSA assuredly has the resources to MITM all of it. Yes, someone at some point would notice if it were all attacked, but the key thing is that, almost all of the time, nobody would, and you yourself have no assurance that your connection has not been MITM'd unless you have done some other out-of-band verification on that specific certificate. That is almost never done, especially by the general public. You might be willing to gamble your own security, but you should not gamble everyone's security.
  - antientropic 13y ago
    There is very little self-signed https traffic out there because browsers have chosen to treat it as somehow less secure than unencrypted http. (I do realise it's rather problematic to mess with the security expectations of https at this point, but you could imagine an http variant that allows encryption without authentication, without giving dire warnings to users.) If all http traffic instead used self-signed https, then the NSA assuredly would not have the resources to MITM all of it. So because of the reflexive "self-signed certificates are worse than no encryption!" dogma, we have an Internet where most traffic is unencrypted and therefore trivial for governments and criminals to intercept. Regarding certificate warnings: even if self-signed certificates were accepted, browsers could still put up a warning if the certificate changes between visits, similar to ssh's treatment of host keys (being relatively unsuspicious of unknown hosts, but putting up a big fat warning if the host key has changed).

devinj 13y ago

Can you MITM public wifi? Real question, but I thought the answer was "no", which would make public wifi a compelling counter-example.

nknighthb 13y ago
I have no idea where you'd get the idea that the answer is "no". The answer is emphatically yes.
syshax 13y ago
Yes. You arp poison the default gateway and route traffic through your own host instead.
- caf 13y ago
  Or spoof DNS responses to point to a machine under your control.
  - sp332 13y ago
    Or spoof a disassociation frame, then impersonate the access point so the victim connects to your computer instead.

antientropic 13y ago

I guess you don't agree with Poul-Henning Kamp in his FOSDEM keynote this year: https://www.youtube.com/watch?v=fwcl17Q0bpk https://www.youtube.com/watch?v=fwcl17Q0bpk (around 15:00) His claim is that browsers treating websites with self-signed certificates as less secure than non-encrypted websites by displaying big fat warnings is just about the greatest gift we can give to organisations like the NSA. It's not true that there is no material distinction between an active attack and passive eavesdropping. For the NSA to do active MITM attacks on all self-signed https traffic (in a world where all unencrypted http is replaced with self-signed https) would take massively more resources than passively monitoring unencrypted traffic. Plus the odds of them getting caught would be very high (since some people are going to notice that the certificate that shows up on the client is not what the server sent).

nknighthb 13y ago
PHK says many things I disagree with. You can't make browsers simply treat self-signed certificates the same as plain HTTP. You still have to warn the user that their desire for a secure connection (conveyed by their request to retrieve an https URL) cannot be fulfilled, and do so in a way that assures all users will notice before they do something like, say, type in their password. There is very little self-signed HTTPS traffic out there. The NSA assuredly has the resources to MITM all of it. Yes, someone at some point would notice if it were all attacked, but the key thing is that, almost all of the time, nobody would, and you yourself have no assurance that your connection has not been MITM'd unless you have done some other out-of-band verification on that specific certificate. That is almost never done, especially by the general public. You might be willing to gamble your own security, but you should not gamble everyone's security.
- antientropic 13y ago
  There is very little self-signed https traffic out there because browsers have chosen to treat it as somehow less secure than unencrypted http. (I do realise it's rather problematic to mess with the security expectations of https at this point, but you could imagine an http variant that allows encryption without authentication, without giving dire warnings to users.) If all http traffic instead used self-signed https, then the NSA assuredly would not have the resources to MITM all of it. So because of the reflexive "self-signed certificates are worse than no encryption!" dogma, we have an Internet where most traffic is unencrypted and therefore trivial for governments and criminals to intercept. Regarding certificate warnings: even if self-signed certificates were accepted, browsers could still put up a warning if the certificate changes between visits, similar to ssh's treatment of host keys (being relatively unsuspicious of unknown hosts, but putting up a big fat warning if the host key has changed).