It's difficult to say how something will be used in the future.
[Med] An advice that is not implementable makes more troubles, IMHO.
My intent (and the understanding of other reviewers) is to highlight that these mechanisms have a privacy-damaging result and that this should be considered.
[Med] I do think existing documents already make that job. I do think we need more.
In particularly, I'm concerned that some application functions in the network (e.g. recursive resolvers or proxies) do not consider the postive privacy implications of their aggregation and so do not consider adding this data back as problematic.
[Med] I’m also concerned with that, too (see e.g., http://www1.icsi.berkeley.edu/
~narseo/papers/hotm42- ). In the meantime, I’m also concerned with (1) some applications that leak privacy information without the consent of the user and (2) some application servers that may correlate various information shared by an application client to track users (e.g., https://panopticlick.eff.org/)vallinarodriguez.pdf . BTW, I see that you are using “application function” which may not have the same meaning as the general “protocol” wording used in draft-hardie-*. Do you consider a DHCP relay as an “application function”? Highlighting this enables them to see this traffic in a different context.
[Med] Isn’t this already assumed by some protocol designers (e.g., RFC6973, SIP)? BTW, there are subtleties when proxies are in the same trust domain of the client or server.
* that data may not be always available to the endhost
Understood, but even in this case, it is better to make the permission to add the data explicit.
[Med] This may be easy to implement for some applications, but this may not be generalized to ** all ** protocols.
The AN intercepts and then tunnels the received Router Solicitation in a newly created IPv6 datagram with the Line-Identification Option (LIO). The AN forms a new IPv6 datagram whose payload is the received Router Solicitation message as described in [RFC2473], except that the Hop Limit field of the Router Solicitation message MUST NOT be decremented.
and asked whether the circuit identifier corresponding to the logical
access loop port of the AN from which the RS was initiated PII. If so, this
document would have them consider whether transparent interception
is the appropriate choice if it is. There clearly are flows in which the AN's role
would be explicit.
I don't know, frankly, which choice is right in this case, but I would prefer that
the choice be made with an easy reference to the implications of inserting metadata
at hand.
Putting aside the interaction with a user to get a consent and how that consent will need to be changed when another user uses the same device to connect to the Internet. Consider a user who does not want an upstream DHPC relay to insert the line-id (https://tools.ietf.org/html/
rfc6788 ) to the server, and let’s suppose the relay received a signal (by some means, to be yet specified) that for this particular DHCP client, the line-id must not be inserted. For this case, connectivity won’t be provided to that user. This would mean extra calls to the hotline for that network provider. This is not desirable for both customers and network providers.
I
f this can be done in parallel with other actions, then the latency impact can be minimized.
[Med] These are assumptions and implications that are worth to be added to the draft.
BTW, this falls into this general discussion in https://tools.ietf.org/html/
rfc6973 :
a. Trade-offs. Does the protocol make trade-offs between privacy
and usability, privacy and efficiency, privacy and
implementability, or privacy and other design goals? Describe
the trade-offs and the rationale for the design chosen.
* a misbehaving node may be tempted to spoof the data to be injected. A remote device that will use that data to enforce policies will be broken.
This point was discussed extensively in the GEOPRIV work and essentially a single carve-out was made: for emergency services, where falsely asserted location data could be used to SWAT individuals or consume safety resources. I don't think that falls into this narrow advice, but I would be willing to add something like this to the security considerations:
"Note that some emergency service recipients, notably PSAPs (Public Safety Answering Points) may prefer data provided by a network to data provided by end system, because an end system could use false data to attack others or consume resources. While this has the consequence that the data available to the PSAP is often more coarse than that available to the end system, the risk of false data being provided involved a risk to the lives of those targeted."
[Med] Thank you. Providing PSAP as an example is OK, but I’d like the issue to be called out as a generic one while PSAP is provided as an example. What about the following:
"Note that some servers (e.g., emergency service recipients, notably PSAPs (Public Safety Answering Points) [RFC6443]) may prefer data provided by a network to data provided by the end system, because an end system could use false data to attack others or consume resources. While this has the consequence that the data available to the server is often more coarse than that available to the end system, the risk of false data being provided involved a risk to the lives of those targeted."
* it was reported in the past that some browsers leak the MSISDN and other sensitive data.
This is true, but it seems to me unrelated to the point of the document.
[Med] It is related because blindly trusting an application client (and server) has its own privacy risks. This is even exacerbated given the rich data that is available to an application client and also because of the visibility on various layers available to an application server.
From that flow some of your other concerns about audience, at least as I understand. As written, this is narrow advice for a broad audience: basically, anyone who would consider the form of metadata insertion it describes. You would, if I understand you, prefer a narrower description of the audience in a larger context.
[Med] The key point here is about the practicality of implementing the advice NOT changing the scope. For example, the document says that it is better that a host is injecting the data but the document does not question whether that supplied data can be trusted or not,
or how the consent will be obtained from a user.
You're right that I'm leaving aside the question of how the user sets the policies, because it may vary by protocol and type of device too much to make general advice useful. If you would like me to add an explicit statement to that effect, I am happy to note that it is not covered.
In general, the point of the document is that the host should be able to omit the data without mid-network devices adding it back. That's the point of protecting the traffic in the first place, after all. I am saying that if the protocols require the data, then getting it from the end host has better privacy properties than getting from it from mid-network entities.
[Med] I’m not sure we can have such general statement because the data may not be available (e.g., DHCP for example) to clients + the data supplied by clients (when possible) may not be reliable + enforcing policies based on client-supplied data may have implication on other users (e.g., spoofing XFF for example). Obviously, getting some of the information from a client may have implications on QoE…the user needs to understand the root causes of a degradation of QoE. Of course, these implications may not be new for users who are familiar with disabling _javascript_s and cie.
For example, the document states that the information in a Forward-For header can be supplied by the host itself and then communicated to a remote consumer. This is indeed possible, but because of abusing hosts some servers implement whitelists to trust proxies; see https://meta.wikimedia.org/w/
extensions/TrustedXFF/trusted- .hosts.txt
The Wikimedia case is a very interesting one to raise, because it derives from a set of assumptions about the network that are somewhat flawed and then attempts to patch those flaws in ways that actually damage the mechanisms of the system they originally built.
Wikimedia wants to allow folks to edit without login credentials. This allows for anonymous users to make corrections or additions; this is a goal. The consequence of that goal being achieved is that trolls or malicious editors can have at anything they want.
Rather than institute credentials and ACLs, Wikimedia attempts to substitute blocking by IP for blocking by credential. The property they are looking for in IPs is not really there, though: they are not unique to individuals, especially over time.
This damages those who share IP addresses (due to NATs or proxies). As far as I can tell, the NAT problem is simply treated as collateral damage. For the proxies, they attempt to work around the damage using XFF. That's spoofable, though, so they attempt to limit it to specific proxies whose XFF they trust--many of which require logins. That shifts the information about who is editing Wikipedia out of their hands, but leaves it in the network and thus not truly anonymous. I understand the engineering balance they are trying to strike, but I'm not sure I can recommend their solution.
[Med] I’m not recommending their solution either, but I’m trying to raise the point that an engineering balance is out there. ACKing that deployment reality is better than ignoring it.