mitigate TLS session resumption tracking

[diracdeltas]

since https://arxiv.org/abs/1810.07304 came out, many people are concerned about the possibility of advertisers tracking people using TLS session resumption data. brave should consider invalidating TLS session resumption tickets periodically to mitigate this.

[jumde]

• Also, restrict the session resumption support for third-parties

[diracdeltas]

discussed in meeting;

WRT tor, if this is not provided by site isolation then we should probably disable TLS ticket caching entirely

[fmarier]

Here are the notes I took after reading the suggested mitigations in that paper:

• ignore new expiry dates to defeat prolongation attacks
• set upper limit for session resumption at 10 min
• disable or double-key session resumption for 3rd-party resources
• disable TLS 1.3 1-RTT session resumption (and therefore 0-RTT)

[diracdeltas]

thanks @fmarier

my current thinking is this would be ideal:

• disable all session resumption mechanisms (including session tickets, session IDs, TLS 1.3 PSKs) in Tor mode
• disable all session resumption mechanisms for 3rd party resources in non-Tor mode
• make sure session resumption state is cleared whenever cookies are cleared

[diracdeltas]

actually according to https://bugs.chromium.org/p/chromium/issues/detail?id=30877, chromium OTR sessions (aka incognito windows) should have session resumption disabled already. if that's the case, Tor mode is protected already

[tildelowengrimm]

Is Tor actually an OTR session though — do guest windows have the same treatment?

[riastradh-brave]

The question about guest sessions will become moot after #2307.

It is unclear to me whether TLS session resumption is actually disabled altogether in off-the-record profiles, or whether it is merely partitioned between normal and off-the-record profiles; this part needs investigation.

That said, upstream is preparing to isolate TLS session caches by network isolation key, which will be the first party, rendering this entirely moot: http://crbug.com/974910

[bsclifton]

@diracdeltas @darkdh would this be fixed now that Tor uses OTR profile?
brave/brave-core#7069