4 ms·

Active attacks are effective and not that risky. For most web services, the attacker only needs to intercept a single transaction in order to get the session co

by tlb 6y ago

Active attacks are effective and not that risky. For most web services, the attacker only needs to intercept a single transaction in order to get the session cookies and then you are pwned. Since they only need one, they can hit you with a DNS cache poisoning attack and simultaneous clickjacking attack while you're on a public WiFi. In general, I'm skeptical of any "this attack isn't really practical" arguments. They have a way of becoming practical enough for high-value targets, so it's not something I want to use.

tptacek 6y ago
This feels like a trap people fall into when considering how attacks work. You're right, any one instance of active TLS interception is vanishingly unlikely to be detected. But an adversary conducting that attack at any kind of scale will be deploying instances of that attack regularly. The cost of detection can be very high --- it's not "public opprobrium", as so often seems to be the mental model on HN, but rather disclosure of sources and methods to other adversaries, who are themselves exquisitely well equipped both to detect stuff and also to work back to expand the scope of tradecraft lapses in drastic and surprising ways. Here, though, it's even simpler: you're positing an attacker who is exploiting a cryptographic vulnerability unknown to science simply in order to conduct an individual TLS interception. The consequences of the disclosure of such an attack --- one that would be discernible by amateurs --- go far beyond what curves people select in the future.
- tlb 6y ago
  The US and a few others routinely sink billions of dollars into weapons systems they'll only ever be able to use once, like strategic nuclear submarines. So the fact that a backdoor could only be used briefly until it was discovered, doesn't mean that some agency wouldn't invest a lot of effort into developing it, just in case.
  - tptacek 6y ago
    Have you read Koblitz and Menezes on this? Section 3.1 goes into more technical details, which are worth reading and easy to follow. https://eprint.iacr.org/2015/1018.pdf https://eprint.iacr.org/2015/1018.pdf
  - deathgrips 6y ago
    The US sinks billions into strategic weapons so that it doesn't have to use them.
temp667 6y ago
Not that risky? This active attack is pretty easy to detect. If you fake a google cert, and chrome hits it (highly likely) game over for you.

by tlb 6y ago

tptacek 6y ago

This feels like a trap people fall into when considering how attacks work. You're right, any one instance of active TLS interception is vanishingly unlikely to be detected. But an adversary conducting that attack at any kind of scale will be deploying instances of that attack regularly. The cost of detection can be very high --- it's not "public opprobrium", as so often seems to be the mental model on HN, but rather disclosure of sources and methods to other adversaries, who are themselves exquisitely well equipped both to detect stuff and also to work back to expand the scope of tradecraft lapses in drastic and surprising ways. Here, though, it's even simpler: you're positing an attacker who is exploiting a cryptographic vulnerability unknown to science simply in order to conduct an individual TLS interception. The consequences of the disclosure of such an attack --- one that would be discernible by amateurs --- go far beyond what curves people select in the future.

tlb 6y ago
The US and a few others routinely sink billions of dollars into weapons systems they'll only ever be able to use once, like strategic nuclear submarines. So the fact that a backdoor could only be used briefly until it was discovered, doesn't mean that some agency wouldn't invest a lot of effort into developing it, just in case.
- tptacek 6y ago
  Have you read Koblitz and Menezes on this? Section 3.1 goes into more technical details, which are worth reading and easy to follow. https://eprint.iacr.org/2015/1018.pdf https://eprint.iacr.org/2015/1018.pdf
- deathgrips 6y ago
  The US sinks billions into strategic weapons so that it doesn't have to use them.

temp667 6y ago

Not that risky? This active attack is pretty easy to detect. If you fake a google cert, and chrome hits it (highly likely) game over for you.