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Update dandelion.md
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Jimmy Debe
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@ -21,8 +21,8 @@ instead of disseminating messages as per usual relay operation.
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## Background and Motivation
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[Waku Relay](https://rfc.vac.dev/waku/standards/core/11/relay), offers privacy, pseudonymity, and a first layer of anonymity protection by design.
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Being a modular protocol family [Waku v2](https://rfc.vac.dev/waku/standards/core/10/waku2)
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[Waku Relay](https://github.com/vacp2p/rfc-index/blob/main/waku/standards/core/11/relay.md), offers privacy, pseudonymity, and a first layer of anonymity protection by design.
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Being a modular protocol family [Waku v2](https://github.com/vacp2p/rfc-index/blob/main/waku/standards/core/10/waku2.md)
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offers features that inherently carry trade-offs as separate building blocks.
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Anonymity protection is such a feature.
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The [Anonymity Trilemma](https://freedom.cs.purdue.edu/projects/trilemma.html)
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@ -37,7 +37,7 @@ and [Dandelion++](https://arxiv.org/abs/1805.11060).
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Dandelion is a message spreading method, which, compared to other methods,
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increases the uncertainty of an attacker when trying to link messages to senders.
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Libp2p gossipsub aims at spanning a [d-regular graph](https://en.wikipedia.org/wiki/Regular_graph) topology, with d=6 as the [default value](https://rfc.vac.dev/spec/29/#gossipsub-v10-parameters).
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Libp2p gossipsub aims at spanning a [d-regular graph](https://en.wikipedia.org/wiki/Regular_graph) topology, with d=6 as the [default value](https://github.com/vacp2p/rfc-index/blob/main/waku/informational/29/config.md/#gossipsub-v10-parameters).
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Messages are forwarded within this (expected) symmetric topology,
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which reduces uncertainty when trying to link messages to senders.
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Dandelion breaks this symmetry by subdividing message spreading into a "stem" and a "fluff" phase.
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@ -61,11 +61,11 @@ Further information on Waku anonymity may be found in our [Waku Privacy and Anon
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## Theory and Functioning
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WAKU2-DANDELION can be seen as an anonymity enhancing add-on to [Waku Relay](https://rfc.vac.dev/waku/standards/core/11/relay) message dissemination,
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WAKU2-DANDELION can be seen as an anonymity enhancing add-on to [Waku Relay](https://github.com/vacp2p/rfc-index/blob/main/waku/standards/core/11/relay.md) message dissemination,
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which is based on [libp2p gossipsub](https://github.com/libp2p/specs/blob/master/pubsub/gossipsub/README.md).
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WAKU2-DANDELION subdivides message dissemination into a "stem" and a "fluff" phase.
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This specification is mainly concerned with specifying the stem phase.
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The fluff phase corresponds to [Waku Relay](https://rfc.vac.dev/waku/standards/core/11/relay),
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The fluff phase corresponds to [Waku Relay](https://github.com/vacp2p/rfc-index/blob/main/waku/standards/core/11/relay.md),
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with optional fluff phase augmentations such as random delays.
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Adding random delay in the fluff phase further reduces symmetry in dissemination patterns and
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introduces more uncertainty for the attacker.
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@ -92,7 +92,7 @@ are always sent as stem messages.
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The stem phase can be seen as a different protocol, and messages are introduced into Waku Relay, and by extension gossipsub,
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once they arrive at a node in fluff state for the first time.
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WAKU2-DANDELION uses [19/WAKU2-LIGHTPUSH](https://rfc.vac.dev/waku/standards/core/19/lightpush) as the protocol for relaying stem messages.
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WAKU2-DANDELION uses [19/WAKU2-LIGHTPUSH](https://github.com/vacp2p/rfc-index/blob/main/waku/standards/core/19/lightpush.md) as the protocol for relaying stem messages.
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There are no negative effects on gossipsub peer scoring,
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because Dandelion nodes in _stem state_ still normally relay Waku Relay (gossipsub) messages.
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@ -116,16 +116,16 @@ corresponding to 10 minute epochs.
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On entering stem state,
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nodes supporting WAKU2-DANDELION MUST randomly select two nodes for each pubsub topic from the respective gossipsub mesh node set.
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These nodes are referred to as stem relays.
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Stem relays MUST support [19/WAKU2-LIGHTPUSH](https://rfc.vac.dev/waku/standards/core/19/lightpush).
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If a chosen peer does not support [19/WAKU2-LIGHTPUSH](https://rfc.vac.dev/waku/standards/core/19/lightpush),
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Stem relays MUST support [19/WAKU2-LIGHTPUSH](https://github.com/vacp2p/rfc-index/blob/main/waku/standards/core/19/lightpush.md).
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If a chosen peer does not support [19/WAKU2-LIGHTPUSH](https://github.com/vacp2p/rfc-index/blob/main/waku/standards/core/19/lightpush.md),
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the node SHOULD switch to fluff state.
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(We may update this strategy in future versions of this document.)
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Further, the node establishes a map that maps each incoming stem connection
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to one of its stem relays chosen at random (but fixed per epoch).
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Incoming stem connections are identified by the [Peer IDs](https://docs.libp2p.io/concepts/peers/#peer-id/)
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of peers the node receives [19/WAKU2-LIGHTPUSH](https://rfc.vac.dev/waku/standards/core/19/lightpush) messages from.
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Incoming [19/WAKU2-LIGHTPUSH](https://rfc.vac.dev/waku/standards/core/19/lightpush) connections from peers that do not support WAKU2-DANDELION are identified and mapped in the same way.
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of peers the node receives [19/WAKU2-LIGHTPUSH](https://github.com/vacp2p/rfc-index/blob/main/waku/standards/core/19/lightpush.md) messages from.
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Incoming [19/WAKU2-LIGHTPUSH](https://github.com/vacp2p/rfc-index/blob/main/waku/standards/core/19/lightpush.md) connections from peers that do not support WAKU2-DANDELION are identified and mapped in the same way.
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This makes the protocol simpler, increases the anonymity set, and offers Dandelion anonymity properties to such peers, too.
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The node itself is mapped in the same way, so that all messages originated by the node are relayed via a per-epoch-fixed Dandelion relay, too.
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@ -133,7 +133,7 @@ The node itself is mapped in the same way, so that all messages originated by th
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While in stem state, nodes MUST relay stem messages to the respective stem relay.
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Received fluff messages MUST be relayed as specified in the fluff state section.
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The stem protocol ([19/WAKU2-LIGHTPUSH](https://rfc.vac.dev/waku/standards/core/19/lightpush)) is independent of the fluff protocol ([Waku Relay](https://rfc.vac.dev/waku/standards/core/11/relay)).
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The stem protocol ([19/WAKU2-LIGHTPUSH](https://github.com/vacp2p/rfc-index/blob/main/waku/standards/core/19/lightpush.md)) is independent of the fluff protocol ([Waku Relay](https://github.com/vacp2p/rfc-index/blob/main/waku/standards/core/11/relay.md)).
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While in stem state, nodes MUST NOT gossip about stem messages,
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and MUST NOT send control messages related to stem messages.
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(An existing gossipsub implementation does _not_ have to be adjusted to not send gossip about stem messages,
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@ -161,7 +161,7 @@ this regular forwarding already comprises random delays.
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## Implementation Notes
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Handling of the WAKU2-DANDELION stem phase can be implemented as an extension to an existing [19/WAKU2-LIGHTPUSH](https://rfc.vac.dev/waku/standards/core/19/lightpush) implementation.
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Handling of the WAKU2-DANDELION stem phase can be implemented as an extension to an existing [19/WAKU2-LIGHTPUSH](https://github.com/vacp2p/rfc-index/blob/main/waku/standards/core/19/lightpush.md) implementation.
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Fluff phase augmentations might alter gossipsub message dissemination (e.g. adding random delays).
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If this is the case, they have to be implemented on the libp2p gossipsub layer.
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@ -197,7 +197,7 @@ WAKU2-DANDELION does not protect against targeted deanonymization attacks.
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Stem relays receiving messages can either be in stem state or in fluff state themselves.
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They might also not support WAKU2-DANDELION,
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and interpret the message as classical [19/WAKU2-LIGHTPUSH](https://rfc.vac.dev/waku/standards/core/19/lightpush),
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and interpret the message as classical [19/WAKU2-LIGHTPUSH](https://github.com/vacp2p/rfc-index/blob/main/waku/standards/core/19/lightpush.md),
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which effectively makes them act as fluff state relays.
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While such peers lower the overall anonymity properties,
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the [Dandelion++ paper](https://arxiv.org/abs/1805.11060)
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@ -234,9 +234,9 @@ We will quantify the resulting loss of anonymity in future versions of this docu
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#### Stem Relay Selection
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In its current version, WAKU2-DANDELION nodes default to fluff state
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if the random stem relay selection yields at least one peer that does not support [19/WAKU2-LIGHTPUSH](https://rfc.vac.dev/waku/standards/core/19/lightpush) (which is the stem protocol used in WAKU2-DANDELION.
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If nodes would reselect peers until they find peers supporting [19/WAKU2-LIGHTPUSH](https://rfc.vac.dev/waku/standards/core/19/lightpush),
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malicious nodes would get an advantage if a significant number of honest nodes would not support [19/WAKU2-LIGHTPUSH](https://rfc.vac.dev/waku/standards/core/19/lightpush).
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if the random stem relay selection yields at least one peer that does not support [19/WAKU2-LIGHTPUSH](https://github.com/vacp2p/rfc-index/blob/main/waku/standards/core/19/lightpush.md) (which is the stem protocol used in WAKU2-DANDELION.
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If nodes would reselect peers until they find peers supporting [19/WAKU2-LIGHTPUSH](https://github.com/vacp2p/rfc-index/blob/main/waku/standards/core/19/lightpush.md),
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malicious nodes would get an advantage if a significant number of honest nodes would not support [19/WAKU2-LIGHTPUSH](https://github.com/vacp2p/rfc-index/blob/main/waku/standards/core/19/lightpush.md).
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Even though this causes messages to enter fluff phase earlier,
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we choose the trade-off in favour of protocol stability and sacrifice a bit of anonymity.
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(We will look into improving this in future versions of this document.)
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@ -254,7 +254,7 @@ We plan to add a separate fluff augmentation specification that will introduce r
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Optimal delay times depend on the message frequency and patterns.
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This delay fluff augmentation specification will be oblivious to the actual message content,
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because Waku Dandelion specifications add anonymity on the routing layer.
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Still, it is important to note that [Waku2 messages](https://rfc.vac.dev/waku/standards/core/14/message/#payloads) (in their current version) carry an originator timestamp,
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Still, it is important to note that [Waku2 messages](https://github.com/vacp2p/rfc-index/blob/main/waku/standards/core/14/message.md/#payloads) (in their current version) carry an originator timestamp,
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which works against fluff phase random delays.
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An analysis of the benefits of this timestamp versus anonymity risks is on our roadmap.
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@ -267,14 +267,14 @@ Note: Introducing random delays can have a negative effect on
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#### Stem Flag
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While WAKU2-DANDELION without fluff augmentation does not effect Waku Relay nodes,
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messages sent by nodes that only support [19/WAKU2-LIGHTPUSH](https://rfc.vac.dev/waku/standards/core/19/lightpush) might be routed through a Dandelion stem without them knowing.
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messages sent by nodes that only support [19/WAKU2-LIGHTPUSH](https://github.com/vacp2p/rfc-index/blob/main/waku/standards/core/19/lightpush.md) might be routed through a Dandelion stem without them knowing.
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While this improves anonymity, as discussed above, it also introduces additional latency and lightpush nodes cannot opt out of this.
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In future versions of this specification we might
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- add a flag to [14/WAKU2-MESSAGE](https://rfc.vac.dev/waku/standards/core/14/message) indicating a message should be routed over a Dandelion stem (opt-in), or
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- add a flag to [14/WAKU2-MESSAGE](https://rfc.vac.dev/waku/standards/core/14/message) indicating a message should _not_ be routed over a Dandelion stem (opt-out), or
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- introducing a fork of [19/WAKU2-LIGHTPUSH](https://rfc.vac.dev/waku/standards/core/19/lightpush) exclusively used for Dandelion stem.
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- add a flag to [14/WAKU2-MESSAGE](https://github.com/vacp2p/rfc-index/blob/main/waku/standards/core/14/message.md) indicating a message should be routed over a Dandelion stem (opt-in), or
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- add a flag to [14/WAKU2-MESSAGE](https://github.com/vacp2p/rfc-index/blob/main/waku/standards/core/14/message.md) indicating a message should _not_ be routed over a Dandelion stem (opt-out), or
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- introducing a fork of [19/WAKU2-LIGHTPUSH](https://github.com/vacp2p/rfc-index/blob/main/waku/standards/core/19/lightpush.md) exclusively used for Dandelion stem.
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In the current version, we decided against these options in favour of a simpler protocol and an increased anonymity set.
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@ -287,11 +287,13 @@ Copyright and related rights waived via [CC0](https://creativecommons.org/public
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- [Dandelion](https://arxiv.org/abs/1701.04439)
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- [Dandelion++](https://arxiv.org/abs/1805.11060)
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- [multi-node (botnet) attacker model](../../informational/adversarial-models.md/#multi-node)
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- [Waku Relay](https://rfc.vac.dev/waku/standards/core/11/relay)
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- [Waku v2](https://rfc.vac.dev/waku/standards/core/10/waku2)
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- [Waku Relay](https://github.com/vacp2p/rfc-index/blob/main/waku/standards/core/11/relay.md)
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- [Waku v2](https://github.com/vacp2p/rfc-index/blob/main/waku/standards/core/10/waku2.md)
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- [d-regular graph](https://en.wikipedia.org/wiki/Regular_graph)
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- [Anonymity Trilemma](https://freedom.cs.purdue.edu/projects/trilemma.html)
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- [Waku Privacy and Anonymity Analysis](https://vac.dev/wakuv2-relay-anon).
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- [On the Anonymity of Peer-To-Peer Network Anonymity Schemes Used by Cryptocurrencies](https://arxiv.org/pdf/2201.11860.pdf)
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- [Adversarial Models](../../informational/adversarial-models.md)
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- [14/WAKU2-MESSAGE](https://rfc.vac.dev/waku/standards/core/14/message)
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- [14/WAKU2-MESSAGE](https://github.com/vacp2p/rfc-index/blob/main/waku/standards/core/14/message.md)
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- [29/WAKU-CONFIG](https://github.com/vacp2p/rfc-index/blob/main/waku/informational/29/config.md)
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- [19/WAKU2-LIGHTPUSH](https://github.com/vacp2p/rfc-index/blob/main/waku/standards/core/19/lightpush.md)
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