Bastien,
For completeness, would you be willing to demonstrate what it might look like
if it were bolt12 in the normal LNURL way? The concern is mostly what you
brought up with relying on DNS entries instead of a typical web server. At
scale, that would be much more difficult for LNURL service providers to
implement for their potentially thousands to millions of users.
Something like Oblivious HTTP could be promising to remove the knowledge of IP
for some of the larger LNURL service providers.
Tony
On 11/16/23 7:51 AM, Bastien TEINTURIER wrote:
> Good morning list,
>
> Most of you already know and love lightning addresses [1].
> I wanted to revisit that protocol, to see how we could improve it and
> fix its privacy drawbacks, while preserving the nice UX improvements
> that it brings.
>
> I have prepared a gist with three different designs that achieve those
> goals [2]. I'm attaching the contents of that gist below. I'd like to
> turn it into a bLIP once I collect enough feedback from the community.
>
> I don't think we should select and implement all three options. They
> show that we have a large enough design space, but I think we should
> aim for simplicity of implementation and deployment. My personal choice
> would be to do options 1 and 3: clients (mobile wallets) would first
> make a DNS request corresponding to option 3, and if that fails, they
> would fallback to option 1. Domain owners would implement only one of
> those two options, depending on their DNS capabilities.
>
> Curious to hear your thoughts!
>
> Many thanks to Rusty and Matt who reviewed early drafts of that gist.
>
> [1] https://lightningaddress.com/
> [2] https://gist.github.com/t-bast/78fd797a7da570d293a8663908d3339b
>
> # Lightning Address
>
> [Lightning Address](
> https://lightningaddress.com/
> ) is a very popular protocol that brings UX improvements that users love.
> We'd like to provide those UX benefits without its privacy and security
> drawbacks.
>
> ## Issues with the current lightning address protocol
>
> As described [here](
> https://github.com/andrerfneves/lightning-address/blob/master/README.md
> ), the lightning address protocol requires payment senders to make an HTTP
> request to the recipient's domain owner.
> This has some inconvenient side effects:
>
> 1. The payment sender reveals their IP address to the recipient's domain
> owner, who knows both the sender and the recipient.
> 2. The domain owner can swap invoices to steal some of the payment.
> 3. It introduces a dependency on DNS servers and the need for an HTTP stack
> on the sender side.
>
> We can do better and fix or mitigate some of these issues, without
> compromising on UX.
> We need two somewhat distinct mechanisms:
>
> 1. A way to privately obtain the `node_id` associated with a given domain.
> 2. A way to privately contact that domain to obtain the recipient's payment
> details.
>
> ## User story
>
> Alice wants to pay `
> b...@domain.com
> ` without any other prior information.
> She doesn't want to reveal:
>
> * her identity to Bob (payment sender privacy)
> * her identity to the manager of `
> domain.com
> ` (payment sender privacy)
> * the fact that she wants to pay `
> b...@domain.com
> ` to her LSP (payment recipient privacy)
>
> ## Option 1: use DNS records to link domains to nodes
>
> A first proposal would be to use a DNS record to obtain the `node_id`
> associated with a given domain.
>
> ### Obtain a blinded path to the node associated with a domain
>
> Domain owners add a DNS `TXT` record for their domain containing a blinded
> path to their node.
> They may include an empty path if they wish to directly reveal their
> `node_id`.
>
> | hostname | record type | value | TTL |
> |------------------------|-------------|---------------------|-------------|
> | _
> lnaddress.domain.com
> . | TXT | path:<blinded_path> | path expiry |
>
> Alice can then make a DNS query to obtain that blinded path.
>
> ```text
> Alice DNS
> server
> | |
> | dig TXT _
> lnaddress.domain.com
> |
> |-------------------------------------------------------------------->|
> | _
> lnaddress.domain.com
> . IN TXT "path:c3056fb73aa623..." |
> |<--------------------------------------------------------------------|
> ```
>
> :question: What encoding should we use for the blinded path option? Bech32m
> with the `lnp` prefix?
>
> :warning: Alice should query that DNS record using [DoH](
> https://datatracker.ietf.org/doc/html/rfc8484
> ) for privacy.
> She should also query multiple DoH servers to protect from malicious ones.
>
> :warning: Alice should check the AD flag is correctly set (DNSSEC).
>
> ### Obtain a Bolt 12 offer from the recipient
>
> Now that Alice has a way to reach the node that owns Bob's domain, she needs
> to contact them to obtain a Bolt 12 offer from Bob.
> We use an `onion_message` for that, which has the following benefits:
>
> * Alice doesn't reveal her identity (IP address or `node_id`) to Bob or Bob's
> domain
> * Alice doesn't reveal Bob's identity (IP address or `node_id`) to her LSP
> * Alice doesn't even need to know the IP address for Bob's domain's lightning
> node
>
> ```text
> Alice Alice's LSP Bob's
> LSP Bob
> | | |
> |
> | onion_message | |
> |
> |-------------------------------->| onion_message |
> |
> | | get_offer_from =
> b...@domain.com
> | |
> | |---------------------------------->|
> |
> | | |
> wake_up |
> | |
> |-------------------------------->|
> | | |
> offer |
> | |
> |<--------------------------------|
> | | onion_message |
> |
> | |<----------------------------------|
> |
> | onion_message | |
> |
> | bob's bolt12 offer | |
> |
> | bob's LSP signature | |
> |
> |<--------------------------------| |
> |
> ```
>
> Note that Alice cannot verify that the offer she receives is really from Bob:
> she has to TOFU (trust on first use).
> But that's something we fundamentally cannot fix if the only information
> Alice has is `
> b...@domain.com
> `.
> However, Alice obtains a signed statement from Bob's LSP that attests that `
> b...@domain.com
> ` is associated with the Bolt12 offer she receives.
> If she later discovers that this was invalid, she can publish that proof to
> show the world that Bob's LSP is malicious.
>
> Otherwise, since there needs to be some out-of-band communication where the
> recipient advertizes their lightning address (e.g. on social media), some
> kind of verification code could be attached (hash of the `node_id`?).
> The sender's wallet could optionally add a manual verification step of that
> verification code.
> This would only need to be done once, since Alice can then reuse the same
> offer to fetch new invoices.
>
> ### Advantages and drawbacks
>
> The main advantage of this proposal is that it is simple, inexpensive and
> relies on standard mechanisms.
> Its drawback is that domain owners need to be able to publish DNS `TXT`
> records, but that is widely supported.
>
> ## Option 2: use `node_announcement` to link nodes to specific domains
>
> This proposal is only based on the lightning network, without any dependency
> on DNS or HTTP stacks (apart from certificate validation).
>
> ### Obtain the `node_id` associated with a domain
>
> We add fields to `node_announcement` to let nodes advertize which domains
> they own.
> Those fields would typically contain a signature of the `node_id` using the
> private key for the corresponding domain TLS certificate, along with its
> certificate chain.
> Alice can then simply sync `node_announcement`s that contain domain links
> with her LSP:
>
> ```text
> Alice LSP
> | |
> | node_announcement(
> foobar.com
> ) |
> |<-----------------------------------------------|
> | node_announcement(
> domain.xyz
> ) |
> |<-----------------------------------------------|
> | node_announcement(ln.stuff) |
> |<-----------------------------------------------|
> | ... |
> |<-----------------------------------------------|
> ```
>
> ### Obtain a Bolt 12 offer from the recipient
>
> This uses exactly the same onion message mechanism as the previous proposal.
>
> ### Advantages and drawbacks
>
> The main advantage of this proposal is that it relies entirely on lightning
> protocol messages.
> Its drawback is that Alice needs to sync some `node_announcement`s to obtain
> the domain owner's `node_id`.
> Alice also needs to validate the certificate chain, which is old school
> annoying crypto.
> It also doesn't allow domain owners to keep their `node_id` private (which
> may be useful for small community-based nodes).
>
> ## Option 3: use DNS records to directly store Bolt 12 offers
>
> Another option would be to make domain owners create one DNS `TXT` record for
> each of their user, directly containing their Bolt 12 offer:
>
> | hostname | record type | value | TTL
> |
> |----------------------------|-------------|---------------------|--------------|
> | bob._
> lnaddress.domain.com
> . | TXT | lno1qqx2n6mw2fh2... | offer expiry |
>
> ```text
> Alice DNS
> server
> | |
> | dig TXT bob._
> lnaddress.domain.com
> |
> |-------------------------------------------------------------------->|
> | bob._
> lnaddress.domain.com
> . IN TXT "lno1qqx2n6mw2fh2..." |
> |<--------------------------------------------------------------------|
> ```
>
> :warning: Alice should query that DNS record using [DoH](
> https://datatracker.ietf.org/doc/html/rfc8484
> ) for privacy.
> She should also query multiple DoH servers to protect from malicious ones.
>
> :warning: Alice should check the AD flag is correctly set (DNSSEC).
>
> ### Advantages and drawbacks
>
> The main advantage of this proposal is that it is straightforward for the
> sender and doesn't require any addition to the lightning protocol.
>
> There are some drawbacks though, mostly for the domain owner, because they
> will need to create a lot of DNS records (one per user).
> If they're using a cloud provider, there will be limitations in the number of
> records they are allowed to create.
> They may not have programmatic access to perform that operation automatically
> (when a user creates their lightning address).
>
> Cheers,
> Bastien
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