Internet-Draft MIMI GLADOS July 2023
Rosenberg Expires 25 January 2024 [Page]
Network Working Group
Intended Status:
J. Rosenberg

Global Lookup and Discovery of Services (GLADOS)


This document proposes a solution for the discovery problem in MIMI (More Instant Messaging Interoperability). The discovery problem is the technique by which a user in one messaging provider can determine the preferred messaging provider for a target user identified by an email address or phone number. The discovery problem has been the subject of numerous - largely failed - standardization attempts at the IETF. This document outlines these attempts and hypothesizes the reasons for their failure, using that to define a set of requirements to avoid these failures in a next attempt. The new proposed solution, called Global Lookup and Discovery of Services (GLADOS), is a distributed service wherein the data is stored and managed by local providers that exchange routing information to facilitate a global lookup capability over a flat namespace.

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This Internet-Draft will expire on 25 January 2024.

Table of Contents

1. Introduction

The More Instant Messaging Interoperability (MIMI) working group is chartered to enable federated messaging, voice, and video service between application providers, such as WhatsApp, Facebook Messenger, and other vendors. The MIMI protocols cover the exchange of encrypted content [I-D.ietf-mimi-content] through transfer protocols [I-D.ralston-mimi-linearized-matrix]. These protocols allow a user in one provider to initiate 1-1 and group messaging with a user in a second provider. The protocol requires that the originator of the communication know two things about the target user - their messaging provider, and a unique identifier for that user within that provider. The specifications recognize that the originator will not always know the provider for the target user, or the provider-specific identifier for that user on that provider. The problem is further complicated by the fact that a users often make use of multiple messaging applications, in which case the preferences of the target user need to be taken into account as well. These preferences are even less likely to be known by the originator of communications.

Rather, in many cases one user will have an email address or phone number for the target user, obtained from their address book on their mobile device. Neither the phone number or email address identify the messaging provider that the target user is using. Unlike email service, the domain portion of a user's email address has no bearing on what messaging provider they use. A user might be using WhatsApp or iMessage, neither of which are Gmail. Thus - the core problem is - how to take one of these service independent identifiers and learn the messaging service that user is using, and what their identifier is on that messaging service.

The MIMI framework hypothesizes the existence of a discovery or directory service to solve this problem. The discovery service would allow the originator to take a servide independent identifier for a target - such as a mobile phone number or email address - and perform a lookup to determine the preferred service of the target user, along with their identifier within that service.

This document proposes a specific solution for the discovery service, a new protocol called the Global Lookup and Discovery of Services (GLADOS). GLADOS is a distributed internet service, interconnecting glados providers (GPs) for the shared global of realizing a global discovery service across different geo-political boundaries. GLADOS is not meant to be directly accessed by consumers. Rather, it is accessed by communications applications operating on a user's behalf.

2. Definitions

3. Prior Efforts

Discovery services are far from new on the Internet.

The whois protocol, originally specified in [RFC0954] and later revised by [RFC3912], was largely focused on the mapping of domain names, to services associated with those domain names, and was one of the first discovery services deployed on the Internet. The DNS SRV record was specified in [RFC2782] and allows a similar discovery process - given a domain name, allows a querier to learn the set of services, such as VOIP based on the Session Initiation Protocol (SIP) [RFC3261] [RFC3263]. Whois and DNS SRV records both assumed that the lookup was keyed by a domain name, and thus they were not that useful for looking up an identifier that is not domain scoped, such as a mobile phone number.

This was first addressed through the specification of ENUM [RFC3761] in 2004. ENUM defined the usage of DNS to lookup phone numbers, by convering a phone number to a DNS name by reversing the digits and adding the suffix "". This allowed portions of the namespace to be delegated to telco providers that owned the number prefix in question. Though technically simple to define, its deployment was hampered by the challenges of establishing authority for the prefixes. It also had a network effects challenge - its utility was limited until there was a critical mass of numbers in the system. It thus became hard to justify the investment of contributing numbers to ENUM. It also suffered from an incentive problem - what was the business value for the telcos to participate in the activity? These challenges resulted in a failure of ENUM adoption.

Another attempt was made with ViPR (Verification Involving PSTN Reahability) [I-D.rosenberg-dispatch-vipr-overview] [I-D.petithuguenin-vipr-pvp]. VIPR made used of a peer-to-peer network based on RELOAD (Resource Location and Discovery) [RFC6940], running between enterprises. It solved the problem of authority problem by authorizing records based on proof of forward routability. However, it had the same network effects problem as ENUM. It also addressed the incentive problem, by focusing on enterprises for which bypassing the phone network would provide cost savings. However, the network effects problem proved insurmountable (amongst other challenges unrelated to the protocol), and it was never widely deployed.

Discovery and lookup services are now common place on the Internet but are scoped entirely within large providers, such as Facebook, Twitter, WhatsApp and other providers.

The MIMI discovery service requires a solution that spans across providers.

4. Core Requirements

There are four key requirements:

  1. Mapping: The service must provide a way to map from a SII to a SSI.

  2. Validity: The mappings provided by the service must be represent the wishes of the user associated with the SII, mapping to an application they are a user of, and the mapped SSI must be the one associated with this user. The core issue is one of trust, and how to determine that the mappings provided by the service are accurate.

  3. Critical Mass: The network effects problem is perhaps the hardest to solve. But, to be viable, any solution must be able to reach a critical mass of mappings so that it becomes useful to consume, and thus useful to further populate.

  4. Incentive Alignment: There must be an incentive structure which motivates the population of mappings into the service, and for the consumption of those mappings.

Beyond these, there are many other requirements related to security and information privacy.

5. GLADOS Overview

Global Lookup and Discovery of Services (GLADOS) is a distributed system that provides the needed mapping function. It is composed of a set of glados providers (GP), each of which hold mappings for a subset of the phone numbers and email addresses in the system overall. The GPs provide services to application providers (AP). The APs are the entities that provide messaging services to end users. The APs would be services like Facebook Messenger or iMessage - the same ones that would participate in the MIMI protocols. The set of APIs between APs and a GP is called the glados client api.

Why multiple GPs? The main rationale is to enable these to be created nationally, with each nation state nominating one (or more) GPs to handle AP's within its jurisdiction. Since each GP stores Personally Identifiable Information (PII), this allows for PII information to be stored only within a specific country or region, a requirement of regulations like the General Data Protection Regulation (GDPR). It also solves for the likely problems in getting everyone to agree on a single provider to use. Glados allows competitive models, where different vendors offer services, and customers (in this case, the APs) can pick which one to purchase from without breaking interconnectivity.

The glados client api is not accessed directly by consumers. Instead, it is accessed indirectly - via the APs. The client API provides three functions:

  1. Mapping query - by which an AP provides an SII and the GP returns the preferred SSI
  2. Bulk registration of mappings from an AP to the GP
  3. Mapping creation via forward routability of emails and/or SMS

A high level view of the relationship between AP, GP and end user is shown below.

            |   GP   |
      |          |          |
 +--------+ +--------+ +--------+
 |  App   | |  App   | |  App   |
 |Provider| |Provider| |Provider|
 |   1    | |   2    | |   3    |
 +--------+ +--------+ +--------+
  |      |    |   |     |      |
  |      +----+   |     |      |
  |      |        |     |      |
+----+ +----+  +----+  +----+ +----+
|User| |User|  |User|  |User| |User|
|  1 | | 2  |  | 3  |  | 4  | | 5  |
+----+ +----+  +----+  +----+ +----+

Figure 1: GLADOS Relationships

An app provider is only ever associated with a single GP. An end user however can be assocated with multiple app providers. This means that, in turn, information about such a user may be present across multiple GP. User two in the above picture is associated with two distinct APs (AP1 and AP2) which in this case are both using the same GP.

The end users never see glados. No end user has an account on it; they dont see it as a brand or know of it. It is rather a service largely invisible to end users, similar to the DNS.

The entities that access glados are application providers. Through an enrollment process, an app provider obtains authorization to access glados for mappings, and to register mappings through either the bulk API or the mapping creation API. As part of this process, an OAuth ClientID and secret are generated, and provided to the app provider. The app provider can uses these to obtain access tokens needed for accessing the glados APIs. Glados APIs are accessed via server-to-server communications, and make use of mutual TLS to provide an additional layer of authentication as well as ensuring that the glados client ID, secret and access tokens remain on the AP's servers and dont make their way to the clients provided by the APs.

Through the bulk registration and mapping creation APIs, each GP will build up a set of mappings. However, each GP will only have a portion of the overall set of mappings. Consequently, when an AP performs a query against its GP for a given SII, that GP may or may not have a mapping for that SII. If it does not, the GP will need to identify which of the other GPs might have the mapping. To facilitate that, the GPs run a protocol between them which exchanges routing information it the form of a bloom filter. The bloom filters - updated continuously via the protocols described below - allow one GP to know definitively that another GP does NOT contain mapping information for an SII. Consequently, when it receives a query from an AP, it creates its own query to all of the other GPs whose bloom filters indicate that a mapping might exist on the GP. The results are collected by the originating GP and returned to the inquiring AP.

6. Glados Provider Creation

In this architecture, the GPs are highly trusted entities. They maintain the authoritative mappings of SII to SSI from the APs. A malicious GP would be destructive to the overall process. It could provide false mappings, resulting in connection requests getting routed to the wrong place. Though MLS - and in particular secure identity - prevents eavesdropping on messages - a malicious GP can cause a DoS attack by black-holing connection requests. Using DNS as an analogy - the GPs are similar to the root zone providers. You dont want just anyone to be running them.

This document proposes a model wherein each nation state formally nominates one or more GPs to serve APs residing in its jurisdiction. A single GP can serve multiple nation states, and a nation state can choose multiple GP. The selected GP for each nation state would be public information, made available through normal governmental communications and publications. Consequently, the proposal here is that there is NOT an actual discovery protocol for finding the set of GP in the world. Rather, they are just well known.

Furthermore, this structure enables GPs to selectively connect with each other. In many ways this is a negative feature - as it will worsen global interconnectedness of messaging. However, it is a recognition of the nationalistic political landscape that is the current reality.

This section is perhaps the most contentious part of this document. Fortunately, decisions on who the GP are on how they are discovered are completely orthogonal to the rest of the protocol and can be changed independently.

7. AP Enrollment

An application provider that wishes to participate in the mimi federation enrolls with a GP.

This enrollment is a manual process, and as part of it, the glados provider will provide a series of audit and validation steps to make sure the app provider is legitimate. This validation process would involve verifying that the app provider is a legitimate business, verifying that their applications are available to consumers on mobile platforms and/or web, validating that the application is indeed a messaging app by creating an account and using it, verifying that it has other users and has reasonable reviews and ratings within app stores. Most importantly, it will try to validate that the application provider is not a source of spam. The GP would define these processes, and they would be made publically available to all.

Why are these checks needed?

The main problem they are trying to solve, is to reduce the risk of the mapping APIs being used for malicious purposes, including spam. Once fully populated, the glados database will contain entries for a significant percentage of the users on the planet, indicating what providers they are using for various communications services. This is valuable information, and could be used for ill. For example, a malicious provider might iterate through the mapping APIs using databases of user email addresses and phone numbers, to build its own directory of users and what apps they are on. It might then send those users spam messages on the various providers. Validating the app providers is one way this is prevented.

Once glados has approved the application vendor, they are provided a traditional OAuth ClientID and Secret, which can be used to obtain access tokens for using the glados APIs.

8. Client API

8.1. Mapping Query

The mapping Query API is a simple REST API that takes, as input, an SII for a target user. The AP sends it to its own GP - called the home GP. The home GP will authorize the request as coming from a valid AP. Once authorized, it returns the preferred SSI for the user. To do that, a multi-step lookup process is performed.

First, the home GP consults its own local set of mappings. If the mapping exists, it next examines the routing tables built from the inter-GP protocols described below. Through those protocols, each GP will basically have a boolean value for each SII which says whether that SII might exist, or definitively does not exist, on another GP. If the home GP finds that the SII definitively does NOT exist on another GP - called remote GPs - and it has a mapping of its own - it returns the mapped SSI. This is the simplest case.

A different case is also one in which the home GP does not have a mapping for the SII. However, its routing tables indicate one or more remote GPs might have the mapping. It performs a query to each of those remote GP, providing the SII in question. The remote GP authorize the request as coming from another GP, and consult only their local mappings when receiving this mapping query. Each remote GP with a match, returns the result to the home GP. In the simplest case, there would be zero or one matches. If it is zero, it means that the target user doesnt exist in glados, and that fact is returned to the AP. If it is one, it means the target user does exist, and the SSI from the remote GP is returned to the AP. In the case of two or more matches, it means that the user might have used multiple applications. Each mapping contains a timestamp, and the most recent result is used. This is part of the distributed preferences algorithm described below.

In the same way, in the case where the home GP has the mapping, it still needs to consult its routing table to see if the mapping might exist on a remote GP. If it finds a match in a remote GP, it compares the timestamp from the remote GP to its own, and uses the most recent.

A sequence diagram for this is shown below.

     ┌──┐          ┌───────┐          ┌──────────┐          ┌──────────┐
     │AP│          │Home GP│          │Remote GP1│          │Remote GP2│
     └┬─┘          └───┬───┘          └────┬─────┘          └────┬─────┘
      │   query SII    │                   │                     │
      │ ──────────────>│                   │                     │
      │                │                   │                     │
      │                │ ╔═════════════════╧════╗                │
      │                │ ║local+routing lookup ░║                │
      │                │ ╚═════════════════╤════╝                │
      │                │    query SII      │                     │
      │                │──────────────────>│                     │
      │                │                   │                     │
      │                │                   │  ╔══════════════╗   │
      │                │                   │  ║local lookup ░║   │
      │                │                   │  ╚══════════════╝   │
      │                │  return result    │                     │
      │                │<──────────────────│                     │
      │                │                   │                     │
      │                │               query SII                 │
      │                │────────────────────────────────────────>│
      │                │                   │                     │
      │                │                   │                     │  ╔══════════════╗
      │                │                   │                     │  ║local lookup ░║
      │                │                   │                     │  ╚══════════════╝
      │                │             return result               │
      │                │<────────────────────────────────────────│
      │                │                   │                     │
      │ return result  │                   │                     │
      │ <──────────────│                   │                     │
     ┌┴─┐          ┌───┴───┐          ┌────┴─────┐          ┌────┴─────┐
     │AP│          │Home GP│          │Remote GP1│          │Remote GP2│
     └──┘          └───────┘          └──────────┘          └──────────┘

Figure 2: Mapping Query

A key requirement for glados is that the GP will impose rate controls to help prevent against the APIs being used maliciously. The GP knows, for any AP, how many users the AP has, because that AP will have to register its own users as described below. With knowledge of how many users the AP has, along with statistics on the typical number of messages sent between providers (and thus the number of mapping requests typically made), the GP can dynamically create reasonable rate limits to make sure that the volume of mapping API requests is reasonable for the provider. This is a second way in which glados prevents the mapping APIs being used for malicious purposes.

Note that the mapping query API is not an enumeration API. It is not possible for an AP to list users. It requires the SII to be provided, and for that SII, it returns the mapped SSI. It is also important to note that the mapping query API is not a batch API either; it is one mapping request at a time. All of these help mitigate against spam and enumeration attacks.

8.2. Mapping Creation

The primary way in which mappings are created in glados are created, is via the mapping creation flow. This flow is shown below:

+-------+                   +-----------+       +---------+
| user  |                   |    AP     |       |   GP    |
+-------+                   +-----------+       +---------+
    |                             |                  |
    | access app                  |                  |
    |---------------------------->|                  |
    |                             |                  |
    |       enter email or number |                  |
    |<----------------------------|                  |
    |                             |                  |
    | SII                         |                  |
    |---------------------------->|                  |
    |                             | ---------------\ |
    |                             |-| create unique| |
    |                             | | userID       | |
    |                             | |--------------| |
    |                             |                  |
    |                             | create map(      |
    |                             |  userID, SII)    |
    |                             |----------------->|
    |                             |                  |
    |                             |   email or SMS   |
    |                             |   with code      |
    |                             |                  |
    | enter code                  |                  |
    |---------------------------->|                  |
    |                             |                  |
    |                             | validation code  |
    |                             |----------------->|
    |                             |                  | ----------\
    |                             |                  |-| store   |
    |                             |                  | |---------|
    |                             |                  |
    |                             | registered       |
    |                             |<-----------------|
    |                             |                  |

Figure 3: Mapping Operation

The mapping operation is best understood by considering the case of a brand new user creating an account on the AP. As part of the new user onboarding process in the app, the user will be prompted to enter their email or mobile number. The AP can choose whether to request email or phone number or both, as a matter of provider policy and design. This is something users are already used to doing as part of application onboarding. The flow described here replaces that flow, with one performed via glados instead whatever SMS or email provider the application provider would have used previously.

The AP will create its own unique ID for the user, scoped within its own application. This ID need only be unique within the application provider. Once the application provider has collected the SII and generated this ID - they are sent to its GP. Using the acccess token, glados will know who the application provider is, and thus be able to construct the SSI by combining the provider userID, with the providerID implied by the access token.

Glados will then construct a short lived code, and either email or SMS it to the user. THe user will receive this text or email, and then copy the code into the app. It is important for the security of this solution that the AP - who is only partially trusted here - does not know this prior to the user entering it. Once the user has entered the code, the AP invokes another API on its GP, providing the code along with the userID provided previously. The GP matches the code with what it had previously sent. If there is a match, it considers the mapping validated, and stores it. It informs the app provider that the code has been confirmed. This allows the app provider to retain its own mapping too, as they do today.

This flow is meant to protect against a malicious AP trying to register mappings that do not actually correspond to their own users. Consider a malicious AP who makes up a set of userIDs, and then tries to register made-up phone numbers or email addresses for those users. They might do this in order to steal messaging or calls targeted to users with those numbers or emails. Consider for example, a malicious provider that tries to register the emails of wealthy CEOs or political leaders, in order to receive messages targeted for them. Should a malicious provider do this, glados will send en email or SMS to that user with the code. The malicious provider does not have that code, and thus would not be able to complete the mapping creation operation.

There are several subcases worth considering.

8.2.1. Mapping Exists on Other AP

Consider the case where AP 1 establishes a mapping for an SII, but a mapping already exists for that SII on a different AP, AP2.

In that case, glados needs to establish a preference, including termination of the prior mapping. To facilitate that, in the response provided to the new AP - AP2 - it will include an indication that there is already a mapping in the old provider AP1, and include that provider ID and name. The new provider would then render to the end user a choice - whether to invalidate the prior mapping, or to keep it and make this new application the preferred one. Using another REST API call, the new provider can then instruct its GP to delete the old mapping or make the new one the preferred choice. This is described in more detail in the section on the Preferences algorithm.

Through a webhook, the old provider AP1 will be notified that the mapping has been removed and/or preference established for the new provider. This will allow the old provider to update there databases, and also inform the user of this change in the old application.

The notification in the old application also helps deal with the case of a malicious AP that always promotes its own app as the preferred app and/or removes the old mapping, against the user's wishes. The old AP will be notified, and this can be shown to the user. If done malicisously, the user can request their old app to re-establish the mapping, change the preference back, or to report the change as malicious. All of those operations would be available to the old AP via API. In the case where the user reports the change as malicious, this would be a strike against the reputation of the new provider. With sufficient strikes, the GP can further rate limit that provider or remove their access entirely.

8.2.2. Phone Number Moves

In this case, user A had a particular phone number, and a registration was made using their app provider AP1. User A then gives up this phone number, and a few months later, it is allocated to user B. User B goes and enters this same phone number - with either the same or a different AP.

In practice, this case is indistinguishable from the prior one. User B would see, in the UI of their app, that a previous registration exists for a different provider. They would then select the option to remove that old mapping for user A.

At the point where user B has obtained the number from their telco, and begun to give it out to friends and family, but has NOT used it with any messaging application, new contact requests for that number will continue to be delivered to user A via their current application. This is definitely not a good thing, and is one of the main limitations of this proposal. It can be somewhat remediated by periodic refresh of the mapping, but this is bothersome to users and is not current practice.

That said, this same limitation exists within existing messaging providers. Glados doesnt make the problem worse, but it doesnt make it better.

8.3. Bulk Registration

A key problem that glados needs to solve is the network effect problem. The mapping creation API above works well, but if we were to depend on that, glados would begin day one with zero phone numbers.

To resolve this, glados will provide a bulk API that allows selected AP to upload mappings, and the GP will just trust them without sending confirmation emails or SMS messages. This API would be made available selectively, only to the handful of known, large providers - Facebook Messenger, WhatsApp, iMessage - and perhaps that's it. With just those three, glados would have critical mass of mappings to bootstrap the ongoing registration process described above, which would be used by all of the other smaller providers and smaller GP too.

The bulk registration process provides full trust in the AP, that they are only registering numbers and email addresses that they have actually verified. This is why it can only be done with the handful of highly known vendors.

The final piece of the puzzle is incentive. What is the incentive for the largest AP to do this? They are, in essence, giving up their crown jewels - a set of validated phone numbers and emails. The answer is the same as mimi as a whole. They would be compelled to do so through the regulatory actions of the EU or other bodies. WIthout that, it is unlikely that this proposal would work.

9. GP to GP Routing Protocol

A key problem to solve, is how one GP can find which other GP to query, when resolving a mapping. One solution is to just do a broadcast query - send the request to all of the other GP. This presents a scale challenge however. The smallest GP - one representing a small country - would need to process a large volume of requests, the vast majority of which are for users outside of its jurisdiction.

A somewhat better approach is to perform a broadcast but then cache negative responses. This only partially mitigates the volume problem, and then relies on a timeout of the negative cache entry. The usage of the negative caching breaks an important user flow - a user signs up for an app, informs their friends out of band, and then their friends send connection requests. With the negative cache, those connection requests will not flow to the user on their new application. This is an unacceptable user experience.

To solve this, glados provides a form of routing protocol, allowing each GP to inform the other GP about what mappings it might hold. Because we are worried about storing PII only within a target country, glados makes use of a bloom filter to exchange this information.

The basic idea is the following.

Each GP has a set of mappings, those mappings being from an SII to an SSI. Each mapping also includes a timestamp. On a periodic basis, every night or every week perhaps, the GP constructs a fresh bloom filter from its mappings. A bloom filter of size 2^N is created and initialized as empty. To add entries into this bloom filter, each SII is hashed using a crypto hash. Of the results, the lowest N bits are selected. The corresponding bit in the bloom filter is set to a one. Each bloom filter has a timestamp, corresponding to the time of creation on the GP.

Each GP provides an API by which the most recent bloom filter can be retrieved. It can easily be encoded as a binary object of size 2N/8 bytes. Since it is large, it would only be retrieved infrequently. Indeed, this is the reason they are versioned. Other GPs can subscribe to additions (but not removals) from that bloom filter.

To support this, when a GP gets a new mapping as described above (via the bulk registration or mapping creation API), it performs the hash over the SII, takes the lower N bits and sets the corresponding bit in the bloom filter to a 1. Of course, mappings can also be removed by a GP. However, removing an entry from the bloom filter incrementally is impossible without completely recomputing it. Because this is likely to be a slow and expensive process, removals are not performed incrementally, only additions.

If the addition of a new SII causes an entry in the bloom filter to flip from a zero to a one, a notification is sent via webhook to any GP that has subscribed. These subscriptions are to a particular version of the bloom filter. When a subscription is created, it also includes a timestamp. The GP will send all changes (which are always transitions in the bloom filter from a zero to a one) since that timestamp. This allows a GP to "catch up" on changes it may have missed when disconnected.

After some period of time - a day or a week perhaps - the old bloom filter is considered sufficiently dirty and is invalidated. A new bloom filter is constructed. Any subscriptions to the old one are terminated, and the other GPs need to fetch the newest one and recreate their subscriptions to receive changes against it.

Bloom filters work really well for this case because there is always going to be a query from a home GP to a remote GP to check if the mapping actually exists. Thus, if the bloom filter has a "1" but its really a "0", the penalty is a wasted query, but no incorrect information.

The use of the subscriptions ensure that - if a new user does sign up - that fact is immediately propagated to the other GPs. This addresses the user experience issue that would otherwise exist with a negative cache that times out.

There are two key parameters this algorithm that need to be tuned - the value of N, and the frequency by which the bloom filter is refreshed.

The value of N is a tradeoff between space efficiency of the encoding, and the volume of traffic that the GP will receive. On one exteme, if N=1 then the system behaves as if there were no filters at all - every query to any other GP will trigger a query to it. This is exactly the traffic problem we are trying to fix. On the other extreme, if a GP has K SIIs in the system, setting N = 2 * log(K) means that every user is almost certainly mapped to a different bit in the bloom filter. Thus, the useful range for any GP is somewhere between 1.. 2*log(K). This spec proposes that each GP can pick whatever value they want for N. However, we should surely propose guidelines which are going to work well.

The second tunable parameter is the frequency by which the bloom filter is refreshed. This depends on the rate at which mappings are deleted relative to the size of the bloom filter. Some modeling work is needed to come up with good suggestions on how to tune this value.

10. Preferences Algorithm

Glados makes an assumption that, at any given time, a user can have a single preferred app provider. This preferred app provider is the one which will receive connection requests from users on different app providers.

When a user has multiple apps, they are given the choice about which one is their preferred provider. The basic algorithm for doing this is simple. When the user utilizes a first application, that application is automatically preferred. SHould the same user (as identified by their SII) utilize a second application, the user is informed that they have already created a preference for the first one. They have the choice to make the new app their preferred one, or keep the old one. If they choose the new one, their new AP asks the GP to delete the old mapping. When the old mapping is deleted, the old AP is informed and they can pass this information on to the user in the old UI.

This approach for preference management avoids the need for there to be a single place that holds the users preferences across multiple APs or GPs, which is critical in a distributed system.

Since glados only partially trusts the APs, a key part of the security of this solution is informing the old AP when a user indicates a preference for the new AP. If the new AP is a malicious provider, and creates this preference without user consent, but the old AP is not malicious, the old AP can inform the user that this preference change has happened, and the user can take action. This is very similar to the email notifications users receive today when there is a change to some kind of configuration on their accounts.

The key to making this work is the propagation of the mapping deletion action back to the old AP.

If the old AP and new AP are on the same GP, this is done via a webhook callback to the old AP. If the old and new AP are on different GP, we dont want to just broadcast the removal. Instead, the GP of the new AP looks into its routing filters to see if any other GP might own a mapping for the SII which has changed. If it finds a match, it sends a webhook callback to those GP, indicating that that particular SII has been claimed. (NOTE: I dont love this. This will cause PII to flow to other GP even if it may not need to, owing to the bloom filters. Still pondering alternatives.)

11. Security Considerations

Security is paramount and is at the center of this proposal.

11.1. Trust Model

There is a three tier trust model which is assumed by glados.

FIrst - are end users. They are completely untrusted and not even first class actors in glados.

Second - are APs. In glados, they are partially trusted. Glados trusts only a few of them to create bulk mappings, but in general, it does not trust them to claim ownership of an SII. This is why the GP validates the mapping via traditional forward routability. Glados partially trusts them to express user preferences correctly, via a "trust but verify" type of model. It trusts them to correctly convey short term validation codes from end users, rather than dropping them or changing them. Should a malicious AP do that, it only hurts their own end user, who will not receive incoming communications from other users outside of that AP.

Finally - are the GPs. In Glados, these are fully trusted. This is why it is necessary to have some kind of procedure for formalizing the creation of GPs. In this document, it is proposed to be done by national selection processes. This is similar to what is done with STIR/SHAKEN, and we might look at reusing some of its policy solutions. We also propose the usage of a nation-state model for creating GPs, in order to allow localized decision making on which other state actors to trust, or not trust (feature or bug, you decide).

11.2. Spam Prevention

The main security worry is that of a malicious messaging provider whose primary interest is the generation of spam. To generate that spam to different users, this malicious messaging provider would take a list of email addresses and phone numbers - all of which are readily obtained - and run a high volume of mapping request operations to obtain an SSI for those users. Using the MIMI protocols, the malicious provider would then spam the user.

This attack is partly mitigated by the MIMI protocols themselves, whih require a user to agree to a connection request from a new user (NOTE: this is not yet finalized as a feature of the protocols). However, this still enables the spamming of connection requests. These connection requests do convey content - a display name, a user identifier, and sometimes an avatar or perhaps even an initial message. More than enough to deliver content and thus an appealing vehicle. The glados protocols provide additional protection from this.

The protection is accomplished through the several aspects of the glados system. First, providers cannot invoke mapping request APIs unless they've enrolled. The enrollment process includes an audit and validation process which ensures the app is a legitimate messaging app. Should a malicious application anyway pass this gate, there is another protection via rate limiting of mapping request invocations. These are rate limited based on the number of enrolled users in the application. A malicious app would need to fake a large number of enrollments to obtain enough rate to usefully spam connection requests. Glados can additionally use analytics to look for odd patterns in registrations, including clearly fake or genreated email addresses, overlaps with existing email addresses and so on.

The spam prevention aspects of glados also make it attractive for app providers to enroll, as another form of incentive.

11.3. Stolen AP Credentials

In this attack, a malicious AP has obtained credentials - clientiD and secret, or access token, for a valid AP.

This is prevented in part through normal techniques - encrypted connections for all glados REST API calls for example.

There is an additional risk - that the clientID and secret and/or access tokens are placed onto the mobile or web application for that provider. A malicious user might try to reverse engineer the client, or inspect memory or disk, in order to get access to these secrets. Given the high privelege associated with these APIs, that is a real risk.

To prevent that, glados adds a requirement for MTLS between the provider and glados. This makes it impossible to use from a web application. Though technically possible in a mobile client, it is unlikely that a legitimate provider would ever place such a certificate on a mobile device. (NOTE: not sure this is really an issue).

12. Informative References

Mahy, R., "More Instant Messaging Interoperability (MIMI) message content", Work in Progress, Internet-Draft, draft-ietf-mimi-content-00, , <>.
Petit-Huguenin, M., Rosenberg, J., and C. F. Jennings, "The Public Switched Telephone Network (PSTN) Validation Protocol (PVP)", Work in Progress, Internet-Draft, draft-petithuguenin-vipr-pvp-04, , <>.
Ralston, T. and M. Hodgson, "Linearized Matrix", Work in Progress, Internet-Draft, draft-ralston-mimi-linearized-matrix-03, , <>.
Rosenberg, J., Jennings, C. F., and M. Petit-Huguenin, "Verification Involving PSTN Reachability: Requirements and Architecture Overview", Work in Progress, Internet-Draft, draft-rosenberg-dispatch-vipr-overview-04, , <>.
Harrenstien, K., Stahl, M., and E. Feinler, "NICNAME/WHOIS", RFC 954, DOI 10.17487/RFC0954, , <>.
Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for specifying the location of services (DNS SRV)", RFC 2782, DOI 10.17487/RFC2782, , <>.
Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, DOI 10.17487/RFC3261, , <>.
Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol (SIP): Locating SIP Servers", RFC 3263, DOI 10.17487/RFC3263, , <>.
Faltstrom, P. and M. Mealling, "The E.164 to Uniform Resource Identifiers (URI) Dynamic Delegation Discovery System (DDDS) Application (ENUM)", RFC 3761, DOI 10.17487/RFC3761, , <>.
Daigle, L., "WHOIS Protocol Specification", RFC 3912, DOI 10.17487/RFC3912, , <>.
Jennings, C., Lowekamp, B., Ed., Rescorla, E., Baset, S., and H. Schulzrinne, "REsource LOcation And Discovery (RELOAD) Base Protocol", RFC 6940, DOI 10.17487/RFC6940, , <>.

Author's Address

Jonathan Rosenberg