3 ms·

Seems like both HTTPS and HTTP/3 can be censored by looking at the Server Name Indication (SNI)? The report says that’s exactly what Russia is doing today. Then

Seems like both HTTPS and HTTP/3 can be censored by looking at the Server Name Indication (SNI)? The report says that’s exactly what Russia is doing today. Then I’m confused by this statement > So, while it is technically still possible to censor HTTP/3 connections based on the SNI in TLS, the collected data shows that hardly any censors actually parse and use this information (even when they do parse the SNI in traditional HTTPS traffic). Most of these countries would use censorship software developed elsewhere. Once this software becomes capable of reading the SNI in HTTP/3 traffic, seems like we would return to the status quo?

vbezhenar 4y ago
AFAIK Russia censorship just drops HTTP 3 connections forcing browsers to downgrade.
tialaramex 4y ago
> Most of these countries would use censorship software developed elsewhere. Once this software becomes capable of reading the SNI in HTTP/3 traffic, seems like we would return to the status quo? Yes. Outside of China countries tend to purchase off-the-shelf middleboxes similar to those a typical US corporation or school might use for this purpose. Actual functionality is not hugely important for these products, the sales person's job is to persuade somebody who controls the purchase decision to give them money, and the actual product capabilities are moot. The problem for such products isn't reading SNI out of an HTTP/3 stream but successfully switching off matching streams. For TLS all they did is shut down the TCP connection on a match. But there is no connection for HTTP/3 because QUIC is a connectionless protocol. So you just get a bunch of UDP packets and now it's your job to figure out which ones to drop as part of your "legitimate network security product". So you can expect "There's an off switch for HTTP/3" plus existing per-network customisations to be the extent of their work for the foreseeable future. If the customer mentions HTTP/3 point them at the switch. Remember that (unlike China) these programmes aren't really focused on practical censorship, because the real goal was achieved once the purchase order paperwork was signed.
- ignoramous 4y ago
  > But there is no connection for HTTP/3 because QUIC is a connectionless protocol. True. Worth pointing out that RFC9000 (QUIC) has deliberate and considerable counter measures against network flow analysis and ossification, in general. Side-effect of that is the middleboxes can't tell one QUIC datagram from another. Almost everything relevant to the middleboxes is either encrypted, obfuscated, or calculated off-band. The masque-wg at IETF are at it, tightening the noose up further. QUIC is connection-ful to its participants, and connection-less to any Mallory snooping in. QUIC enforces the end-to-end principle.
- Matthias247 4y ago
  > The problem for such products isn't reading SNI out of an HTTP/3 stream but successfully switching off matching streams. For TLS all they did is shut down the TCP connection on a match. But there is no connection for HTTP/3 because QUIC is a connectionless protocol. This is not true. QUIC is a Protocol that features a stateful connection. On top of that connection multiple streams are multiplexed. The SNI information is transmitted as part of the TLS ClientHello - which is transferred on connection establishment (before any streams and anything related to HTTP/3 exists). QUIC is running on top of a connectionless protocol (UDP) - but that doesn’t make it connectionless only itself. Same with TCP - it isn’t connectionless just because it runs on top of IP.
  - tialaramex 4y ago
    Sure, that wording was misleading. For the two peers using QUIC there's a connection, but for the middlebox no discernible connection exists, and so it can't shut down that connection.

vbezhenar 4y ago

AFAIK Russia censorship just drops HTTP 3 connections forcing browsers to downgrade.

tialaramex 4y ago

> Most of these countries would use censorship software developed elsewhere. Once this software becomes capable of reading the SNI in HTTP/3 traffic, seems like we would return to the status quo? Yes. Outside of China countries tend to purchase off-the-shelf middleboxes similar to those a typical US corporation or school might use for this purpose. Actual functionality is not hugely important for these products, the sales person's job is to persuade somebody who controls the purchase decision to give them money, and the actual product capabilities are moot. The problem for such products isn't reading SNI out of an HTTP/3 stream but successfully switching off matching streams. For TLS all they did is shut down the TCP connection on a match. But there is no connection for HTTP/3 because QUIC is a connectionless protocol. So you just get a bunch of UDP packets and now it's your job to figure out which ones to drop as part of your "legitimate network security product". So you can expect "There's an off switch for HTTP/3" plus existing per-network customisations to be the extent of their work for the foreseeable future. If the customer mentions HTTP/3 point them at the switch. Remember that (unlike China) these programmes aren't really focused on practical censorship, because the real goal was achieved once the purchase order paperwork was signed.

ignoramous 4y ago
> But there is no connection for HTTP/3 because QUIC is a connectionless protocol. True. Worth pointing out that RFC9000 (QUIC) has deliberate and considerable counter measures against network flow analysis and ossification, in general. Side-effect of that is the middleboxes can't tell one QUIC datagram from another. Almost everything relevant to the middleboxes is either encrypted, obfuscated, or calculated off-band. The masque-wg at IETF are at it, tightening the noose up further. QUIC is connection-ful to its participants, and connection-less to any Mallory snooping in. QUIC enforces the end-to-end principle.
Matthias247 4y ago
> The problem for such products isn't reading SNI out of an HTTP/3 stream but successfully switching off matching streams. For TLS all they did is shut down the TCP connection on a match. But there is no connection for HTTP/3 because QUIC is a connectionless protocol. This is not true. QUIC is a Protocol that features a stateful connection. On top of that connection multiple streams are multiplexed. The SNI information is transmitted as part of the TLS ClientHello - which is transferred on connection establishment (before any streams and anything related to HTTP/3 exists). QUIC is running on top of a connectionless protocol (UDP) - but that doesn’t make it connectionless only itself. Same with TCP - it isn’t connectionless just because it runs on top of IP.
- tialaramex 4y ago
  Sure, that wording was misleading. For the two peers using QUIC there's a connection, but for the middlebox no discernible connection exists, and so it can't shut down that connection.