7 ms·

Encryption App ‘Signal’ Fights Censorship with a Clever Workaround

102 points by ergot 10y ago

subliminalpanda 10y ago
I asked my aunt in Dubai to update Signal on her iPhone and managed to place a call sans VPN. Completely stable, clear audio.
- vinay427 10y ago
  The quality has never been stellar for me. It's similar to speaking on a landline, but not nearly as good as VoLTE or some online systems (Hangouts excepted, because their quality is poor every time I've used it). I've tried it between the US and US/Europe, for what it's worth, over mobile internet connections.
  - subliminalpanda 10y ago
    To put it into perspective, audio call quality is much better on WhatsApp by comparison. However due to my family member connecting to a VPN the additional latency would cause audio jitters. Calls would also drop after 10-15 minutes. With this technique the jitters have all but gone, and no disconnections.
rhcom2 10y ago
Can someone explain to me why Tor does not use "domain fronting" to hide that it is Tor traffic?
- carbocation 10y ago
  From the article: > That domain fronting technique has already been used by other encryption and anti-censorship tools like Tor, Psiphon, and Lantern. (This doesn't answer your question, but it does raise the possibility that it's begging the question.)
- chrisballinger 10y ago
  This is exactly what the meek [1] pluggable transport does. It was developed by David Fifield, of the original authors of the domain fronting paper [2]. 1. https://trac.torproject.org/projects/tor/wiki/doc/meek https://trac.torproject.org/projects/tor/wiki/doc/meek 2. https://www.bamsoftware.com/papers/fronting/ https://www.bamsoftware.com/papers/fronting/
  - rhcom2 10y ago
    Thanks a lot for the links. So am I correct in understanding that the reason this isn't a default Tor capability is the setup around the domains used to do the fronting (looks like meek uses mostly CDNs?)
ergot 10y ago
Here's a detailed overview of so called 'domain fronting' https://www.bamsoftware.com/papers/fronting/ https://www.bamsoftware.com/papers/fronting/ Some VPNs use a module called obfsproxy which uses the fronting technique. One VPN service I recall using it is called Tunnelbear. You can read more about this feature here: https://help.tunnelbear.com/customer/en/portal/articles/2435665-ghostbear-fight-censorship-and-restrictive-networks https://help.tunnelbear.com/customer/en/portal/articles/2435... This is not an endorsement of Tunnelbear, I just thought it would be noteworthy mentioning that VPN services offer this now to thwart censorship.
- tornadoboy55 10y ago
  OpenVPN goes over TCP port 443, making it look like bog-standard HTTPS traffic. Unless the country you're in blacklists entire VPN IP blocks (not particularly useful, they rotate all the time), it's already unblockable, unless they want to block ALL https traffic.
  - ergot 10y ago
    The idea behind obfsproxy is that you don't want it looking like port 443 on the wire. You can infact mask the traffic using the domain fronting technique providing you setup obfsproxy correctly. I haven't tried it myself, but I have analyzed Tunnelbear's 'ghostbear' feature with wireshark and the traffic looks fairly innocuous which is what we're aiming for. https://community.openvpn.net/openvpn/wiki/TrafficObfuscation https://community.openvpn.net/openvpn/wiki/TrafficObfuscatio...
  - rahimnathwani 10y ago
    It's easy to distinguish. Why would your IP address have a single high-traffic HTTPS session going for hours, to the same IP address, every day? I live in China and OpenVPN on TCP 443 hasn't worked reliably for the past few years, and even switching ports frequently is no longer a solution. Regular HTTPS works fine, and isn't blocked.
  - subliminalpanda 10y ago
    OpenVPN can be configured to go over TCP port 443, but it can run on any port number, TCP or UDP.
grandalf 10y ago
This is great until we realize that Google is a friend of oppressive regimes and will turn over data without requiring a warrant to the regimes.
- pilif 10y ago
  It's still end-to-end encrypted though, so all google can hand over is random data.
  - grandalf 10y ago
    Not with app engine's default cert that matches *.google.com Google has the private keys and would likely happily siphon off any data requested by said regimes.
    - penagwin 10y ago
      But send google data that is encrypted with your keys. You encrypt the message, and then encrypt it AGAIN with google certs. So all google sees are encrypted messages.
    - cyphar 10y ago
      > Not with app engine's default cert that matches *.google.com The actual messages are encrypted by Signal's crypto, not just SSL. Signal is just using Google as a dumb transport layer. Tor has a similar censorship circumvention mode which uses its own crypto over an SSL connection to App Engine I'm not a fan of Google, but you're just spreading FUD.
      - grandalf 10y ago
        Do you think Google would decline to provide IP addresses or logs or any other information to the regimes?
        cyphar 10y ago
        ISPs in those countries would already have that information, so if you're in such a regime Google will not add any extra concerns in that regard. Not to mention that Signal does actually work if you tunnel it over Tor (you have to root your phone and force everything through it). So if someone was _really_ worried they could use Tor as well. You're still spreading FUD.
linkregister 10y ago
This is a great workaround for the UAE and Saudi, which are "oppression lite." This would never work in a more oppressive country; the rulers there would simply fail to whitelist traffic going to Google Cloud / App Engine traffic. This is already evident on the other side of the Great Firewall. Still, pretty cool.
- trome 10y ago
  If they block Google.com sure, it won't work, but in that case Signal could just use a CDN they won't block, like Alicloud in China, or AWS or similar.
  - Fnoord 10y ago
    Signal can use Cloudflare as well (the article I read first spoke of Cloudflare, not Google, but it wasn't in English). Blocking Cloudflare is going to break half the internet.
    - ycmbntrthrwaway 10y ago
      In Russia, Roskomnadzor does not care. The number of blocked CloudFlare IPs in Russia keeps growing and about one third of blocked IPs belong to CloudFlare: https://rublacklist.net/13108/ https://rublacklist.net/13108/ It is still a small percentage of CloudFlare IPs, but if you use free CloudFlare service for your website you are extremely likely to get IP that is already blocked. Actually, Roskomnadzor officially asked not to use CloudFlare sites: http://rkn.gov.ru/news/rsoc/news24880.htm http://rkn.gov.ru/news/rsoc/news24880.htm The message is don't hide behind CloudFlare or your sites will get blocked by IP without reason. China blocks Google fonts, it breaks half the internet by making all fonts requests timeout, but still the government does not care. When government starts blocking CDNs, most commercial websites aiming at users within the government will rapidly move off the CDN instead of freedom fighting, sadly.
devy 10y ago
This "domain fronting" trick could make Google suffer collateral damages if the regime is determined to block such encryption apps.
- 01Michael10 10y ago
  It's OK, Google would survive just fine... The real worry is the people who need secure communications and their survival.
  - trome 10y ago
    Yeah, Google will survive this just fine. Signal users and activists are a higher priority than the risk to Google, since the risks in UAE aren't terribly high for them. Blocking Google would make Dubai really look like a red headed step child, since they are trying to appeal to an international audience to do business and live in their country. Porn they are able to get away with blocking, but basic tools for business is unlikely to get blocked, especially since their competitors (Yandex & Baidu) are not popular there.
  - devy 10y ago
    Collateral damages not in ways of Internet traffic but getting "blocked" in those regions.
    - 01Michael10 10y ago
      Yes, we know... And?
  - devy 10y ago
    Collateral damages not in ways of Internet traffic but getting "blocked" in those regions.
Jarwain 10y ago
Here's a link to the blog post announcing the update. https://whispersystems.org/blog/doodles-stickers-censorship/ https://whispersystems.org/blog/doodles-stickers-censorship/ I find it amusing the stark difference; going from light hearted doodles and stickers on images to a censoring workaround
xref 10y ago
So could the AppEngine subdomain that Signal is using be DDoSed to make it timeout (or run up their bill fantastically high) when the domain fronted message is forwarded?

102 points by ergot 10y ago

I asked my aunt in Dubai to update Signal on her iPhone and managed to place a call sans VPN. Completely stable, clear audio.

vinay427 10y ago
The quality has never been stellar for me. It's similar to speaking on a landline, but not nearly as good as VoLTE or some online systems (Hangouts excepted, because their quality is poor every time I've used it). I've tried it between the US and US/Europe, for what it's worth, over mobile internet connections.
- subliminalpanda 10y ago
  To put it into perspective, audio call quality is much better on WhatsApp by comparison. However due to my family member connecting to a VPN the additional latency would cause audio jitters. Calls would also drop after 10-15 minutes. With this technique the jitters have all but gone, and no disconnections.

rhcom2 10y ago

Can someone explain to me why Tor does not use "domain fronting" to hide that it is Tor traffic?

carbocation 10y ago
From the article: > That domain fronting technique has already been used by other encryption and anti-censorship tools like Tor, Psiphon, and Lantern. (This doesn't answer your question, but it does raise the possibility that it's begging the question.)
chrisballinger 10y ago
This is exactly what the meek [1] pluggable transport does. It was developed by David Fifield, of the original authors of the domain fronting paper [2]. 1. https://trac.torproject.org/projects/tor/wiki/doc/meek https://trac.torproject.org/projects/tor/wiki/doc/meek 2. https://www.bamsoftware.com/papers/fronting/ https://www.bamsoftware.com/papers/fronting/
- rhcom2 10y ago
  Thanks a lot for the links. So am I correct in understanding that the reason this isn't a default Tor capability is the setup around the domains used to do the fronting (looks like meek uses mostly CDNs?)

ergot 10y ago

Here's a detailed overview of so called 'domain fronting' https://www.bamsoftware.com/papers/fronting/ https://www.bamsoftware.com/papers/fronting/ Some VPNs use a module called obfsproxy which uses the fronting technique. One VPN service I recall using it is called Tunnelbear. You can read more about this feature here: https://help.tunnelbear.com/customer/en/portal/articles/2435665-ghostbear-fight-censorship-and-restrictive-networks https://help.tunnelbear.com/customer/en/portal/articles/2435... This is not an endorsement of Tunnelbear, I just thought it would be noteworthy mentioning that VPN services offer this now to thwart censorship.

tornadoboy55 10y ago
OpenVPN goes over TCP port 443, making it look like bog-standard HTTPS traffic. Unless the country you're in blacklists entire VPN IP blocks (not particularly useful, they rotate all the time), it's already unblockable, unless they want to block ALL https traffic.
- ergot 10y ago
  The idea behind obfsproxy is that you don't want it looking like port 443 on the wire. You can infact mask the traffic using the domain fronting technique providing you setup obfsproxy correctly. I haven't tried it myself, but I have analyzed Tunnelbear's 'ghostbear' feature with wireshark and the traffic looks fairly innocuous which is what we're aiming for. https://community.openvpn.net/openvpn/wiki/TrafficObfuscation https://community.openvpn.net/openvpn/wiki/TrafficObfuscatio...
- rahimnathwani 10y ago
  It's easy to distinguish. Why would your IP address have a single high-traffic HTTPS session going for hours, to the same IP address, every day? I live in China and OpenVPN on TCP 443 hasn't worked reliably for the past few years, and even switching ports frequently is no longer a solution. Regular HTTPS works fine, and isn't blocked.
- subliminalpanda 10y ago
  OpenVPN can be configured to go over TCP port 443, but it can run on any port number, TCP or UDP.

grandalf 10y ago

This is great until we realize that Google is a friend of oppressive regimes and will turn over data without requiring a warrant to the regimes.

pilif 10y ago
It's still end-to-end encrypted though, so all google can hand over is random data.
- grandalf 10y ago
  Not with app engine's default cert that matches *.google.com Google has the private keys and would likely happily siphon off any data requested by said regimes.
  - penagwin 10y ago
    But send google data that is encrypted with your keys. You encrypt the message, and then encrypt it AGAIN with google certs. So all google sees are encrypted messages.
  - cyphar 10y ago
    > Not with app engine's default cert that matches *.google.com The actual messages are encrypted by Signal's crypto, not just SSL. Signal is just using Google as a dumb transport layer. Tor has a similar censorship circumvention mode which uses its own crypto over an SSL connection to App Engine I'm not a fan of Google, but you're just spreading FUD.
    - grandalf 10y ago
      Do you think Google would decline to provide IP addresses or logs or any other information to the regimes?
      - cyphar 10y ago
        ISPs in those countries would already have that information, so if you're in such a regime Google will not add any extra concerns in that regard. Not to mention that Signal does actually work if you tunnel it over Tor (you have to root your phone and force everything through it). So if someone was _really_ worried they could use Tor as well. You're still spreading FUD.

linkregister 10y ago

This is a great workaround for the UAE and Saudi, which are "oppression lite." This would never work in a more oppressive country; the rulers there would simply fail to whitelist traffic going to Google Cloud / App Engine traffic. This is already evident on the other side of the Great Firewall. Still, pretty cool.

trome 10y ago
If they block Google.com sure, it won't work, but in that case Signal could just use a CDN they won't block, like Alicloud in China, or AWS or similar.
- Fnoord 10y ago
  Signal can use Cloudflare as well (the article I read first spoke of Cloudflare, not Google, but it wasn't in English). Blocking Cloudflare is going to break half the internet.
  - ycmbntrthrwaway 10y ago
    In Russia, Roskomnadzor does not care. The number of blocked CloudFlare IPs in Russia keeps growing and about one third of blocked IPs belong to CloudFlare: https://rublacklist.net/13108/ https://rublacklist.net/13108/ It is still a small percentage of CloudFlare IPs, but if you use free CloudFlare service for your website you are extremely likely to get IP that is already blocked. Actually, Roskomnadzor officially asked not to use CloudFlare sites: http://rkn.gov.ru/news/rsoc/news24880.htm http://rkn.gov.ru/news/rsoc/news24880.htm The message is don't hide behind CloudFlare or your sites will get blocked by IP without reason. China blocks Google fonts, it breaks half the internet by making all fonts requests timeout, but still the government does not care. When government starts blocking CDNs, most commercial websites aiming at users within the government will rapidly move off the CDN instead of freedom fighting, sadly.

devy 10y ago

This "domain fronting" trick could make Google suffer collateral damages if the regime is determined to block such encryption apps.

01Michael10 10y ago
It's OK, Google would survive just fine... The real worry is the people who need secure communications and their survival.
- trome 10y ago
  Yeah, Google will survive this just fine. Signal users and activists are a higher priority than the risk to Google, since the risks in UAE aren't terribly high for them. Blocking Google would make Dubai really look like a red headed step child, since they are trying to appeal to an international audience to do business and live in their country. Porn they are able to get away with blocking, but basic tools for business is unlikely to get blocked, especially since their competitors (Yandex & Baidu) are not popular there.
- devy 10y ago
  Collateral damages not in ways of Internet traffic but getting "blocked" in those regions.
  - 01Michael10 10y ago
    Yes, we know... And?
- devy 10y ago
  Collateral damages not in ways of Internet traffic but getting "blocked" in those regions.

Jarwain 10y ago

Here's a link to the blog post announcing the update. https://whispersystems.org/blog/doodles-stickers-censorship/ https://whispersystems.org/blog/doodles-stickers-censorship/ I find it amusing the stark difference; going from light hearted doodles and stickers on images to a censoring workaround

xref 10y ago

So could the AppEngine subdomain that Signal is using be DDoSed to make it timeout (or run up their bill fantastically high) when the domain fronted message is forwarded?