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Here is a very interesting perspective from a guy called Andersen Cheng who developed an encrypted messaging app - before removing it from the public domain giv

by retube 5y ago

Here is a very interesting perspective from a guy called Andersen Cheng who developed an encrypted messaging app - before removing it from the public domain given its adoption by Islamic State: https://www.ft.com/content/00e6b9d5-a9a2-488d-821f-de6813ca4053 https://www.ft.com/content/00e6b9d5-a9a2-488d-821f-de6813ca4... His proposal is for "threshold cryptography" as a trade off between privacy and allowing law enforcement to do their thing when necessary: to break a message would require agreement / input from multiple parties, including the courts. I think potentially a good compromise.

SamBam 5y ago
I can't read the article, but naively to me this sounds like it requires the app-owner to be able to access the messages when requested, and so whatever thresholds they say they're adhering to (courts, etc), as an end-user I can't know if they might change their minds at some point and read all my messages.
- 3np 5y ago
  While what you're saying is how it may play out in practice (which is, I argue, the case for any closed-source client), it's not necessary when using threshold encryption; you can construct an encrypted message such that K out of N keys can be combined to decrypt the ciphertext. If those public keys are on the client, it does not require the message to be sent to a trusted server. mtgx's comment points to some practical implementation and logistics issues, though. Never mind how one would handle key revokations... --- In case of the main article, though, that's irrelevant, as an e-mail provider necessarily has access to each unencrypted e-mail as they deliver them to and from the user. I can see it being the least bad way to log messages (if they would need to do so). Rather than logging in cleartext, or encrypting with a single key, it could be a threshold encryption where, say, more than one entity inside law enforcement/high court/etc are required in order to decrypt intercepted traffic. I think our learned instinct has become to say "yeah, would be nice but good luck making anyone implement that"... But why not?
marcus_holmes 5y ago
That looks interesting, but needs an FT subscription to read which makes it rather pointless.
mtgx 5y ago
Would each "court" have their individual private key? Would that key only work for cases happening in that area? Otherwise, once there is a key (or let's say 5) that work across all cases, those will be stolen and abused.
gruez 5y ago
>His proposal is for "threshold cryptography" as a trade off between privacy and allowing law enforcement to do their thing when necessary: to break a message would require agreement / input from multiple parties, including the courts Isn't this just key escrow by another name?
- jlokier 5y ago
  Depends what it is done. It could be implemented in a more structured way than escrow of, say, an entire account would be. For example the ability to open specific mails, specific conversations or with specific other parties under particular conditions, without revealing metadata of the rest. Or conditions like "if the person X communicated several times in a month with person of interest Y during the time crime Z occurred, open it up, but don't reveal the existence of anything outside that". You can think of that as escrow of each message separately and just enough to match which messages you're looking for, while keeping the as much as possible about the others private. But actually doing it takes sophisticated cryptography still at the leading edge of research.
MikeUt 5y ago
> allowing law enforcement to do their thing when necessary "their thing" being pointing a telescopic lens at a suspect as they enter their password, or planting a hardware keylogger when they leave their computer unattended? Or is "their thing" more like mass surveillance of everyone? Does Cheng feel car manufacturers have a responsibility to plant microphones in their vehicles, with "threshold encryption" keeping conversations in that car secret? What about construction companies? Law enforcement has no way to retroactively get a record of all conversations that took place in a room, even with a valid warrant. Does that make rooms beyond the reach of law enforcement? What other everyday tools we consider "ours" should be required to betray us if whatever threshold he proposes is reached? And only the good governments will be able to reach these thresholds, right? If you look back through history, the risk of one's own government turning against them is so low, we should have no qualms about surrounding ourselves with tools ready to turn on us, should the state ask them to?

by retube 5y ago

SamBam 5y ago

I can't read the article, but naively to me this sounds like it requires the app-owner to be able to access the messages when requested, and so whatever thresholds they say they're adhering to (courts, etc), as an end-user I can't know if they might change their minds at some point and read all my messages.

3np 5y ago
While what you're saying is how it may play out in practice (which is, I argue, the case for any closed-source client), it's not necessary when using threshold encryption; you can construct an encrypted message such that K out of N keys can be combined to decrypt the ciphertext. If those public keys are on the client, it does not require the message to be sent to a trusted server. mtgx's comment points to some practical implementation and logistics issues, though. Never mind how one would handle key revokations... --- In case of the main article, though, that's irrelevant, as an e-mail provider necessarily has access to each unencrypted e-mail as they deliver them to and from the user. I can see it being the least bad way to log messages (if they would need to do so). Rather than logging in cleartext, or encrypting with a single key, it could be a threshold encryption where, say, more than one entity inside law enforcement/high court/etc are required in order to decrypt intercepted traffic. I think our learned instinct has become to say "yeah, would be nice but good luck making anyone implement that"... But why not?

marcus_holmes 5y ago

That looks interesting, but needs an FT subscription to read which makes it rather pointless.

mtgx 5y ago

Would each "court" have their individual private key? Would that key only work for cases happening in that area? Otherwise, once there is a key (or let's say 5) that work across all cases, those will be stolen and abused.

gruez 5y ago

>His proposal is for "threshold cryptography" as a trade off between privacy and allowing law enforcement to do their thing when necessary: to break a message would require agreement / input from multiple parties, including the courts Isn't this just key escrow by another name?

jlokier 5y ago
Depends what it is done. It could be implemented in a more structured way than escrow of, say, an entire account would be. For example the ability to open specific mails, specific conversations or with specific other parties under particular conditions, without revealing metadata of the rest. Or conditions like "if the person X communicated several times in a month with person of interest Y during the time crime Z occurred, open it up, but don't reveal the existence of anything outside that". You can think of that as escrow of each message separately and just enough to match which messages you're looking for, while keeping the as much as possible about the others private. But actually doing it takes sophisticated cryptography still at the leading edge of research.

MikeUt 5y ago

> allowing law enforcement to do their thing when necessary "their thing" being pointing a telescopic lens at a suspect as they enter their password, or planting a hardware keylogger when they leave their computer unattended? Or is "their thing" more like mass surveillance of everyone? Does Cheng feel car manufacturers have a responsibility to plant microphones in their vehicles, with "threshold encryption" keeping conversations in that car secret? What about construction companies? Law enforcement has no way to retroactively get a record of all conversations that took place in a room, even with a valid warrant. Does that make rooms beyond the reach of law enforcement? What other everyday tools we consider "ours" should be required to betray us if whatever threshold he proposes is reached? And only the good governments will be able to reach these thresholds, right? If you look back through history, the risk of one's own government turning against them is so low, we should have no qualms about surrounding ourselves with tools ready to turn on us, should the state ask them to?