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Add support for contacts as specified in bLIP 42. Contacts are mutually authenticated using a 32-bytes random secret generated when first adding a node to our contacts. When paying contacts, we include our own payment information to allow them to pay us back and us to their contacts. The benefit of this design is that offers stay private by default (they don't include any contact information). It's only when we pay someone we trust that we reveal contact information (which they are free to ignore). The drawback of this design is that if when both nodes independently add each other to their contacts list, they generate a different contact secret: users must manually associate incoming payments to an existing contact to correctly identify incoming payments (by storing multiple secrets for such contacts). This also happens when contacts use multiple wallets, which will all use different contact secrets. I think this is an acceptable trade-off to preserve privacy by default. More details in the bLIP: lightning/blips#42
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src/commonMain/kotlin/fr/acinq/lightning/payment/Contacts.kt
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| package fr.acinq.lightning.payment | ||
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| import fr.acinq.bitcoin.ByteVector32 | ||
| import fr.acinq.bitcoin.Crypto | ||
| import fr.acinq.bitcoin.byteVector32 | ||
| import fr.acinq.lightning.wire.OfferTypes | ||
| import io.ktor.utils.io.core.* | ||
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| /** | ||
| * BIP 353 human-readable address of a contact. | ||
| */ | ||
| data class ContactAddress(val name: String, val domain: String) { | ||
| init { | ||
| require(name.length < 256) { "bip353 name must be smaller than 256 characters" } | ||
| require(domain.length < 256) { "bip353 domain must be smaller than 256 characters" } | ||
| } | ||
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| override fun toString(): String = "$name@$domain" | ||
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| companion object { | ||
| fun fromString(address: String): ContactAddress? { | ||
| val parts = address.replace("₿", "").split('@') | ||
| return when { | ||
| parts.size != 2 -> null | ||
| parts.any { it.length > 255 } -> null | ||
| else -> ContactAddress(parts.first(), parts.last()) | ||
| } | ||
| } | ||
| } | ||
| } | ||
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| /** | ||
| * Contact secrets are used to mutually authenticate payments. | ||
| * | ||
| * The first node to add the other to its contacts list will generate the [primarySecret] and send it when paying. | ||
| * If the second node adds the first node to its contacts list from the received payment, it will use the same | ||
| * [primarySecret] and both nodes are able to identify payments from each other. | ||
| * | ||
| * But if the second node independently added the first node to its contacts list, it may have generated a | ||
| * different [primarySecret]. Each node has a different [primarySecret], but they will store the other node's | ||
| * [primarySecret] in their [additionalRemoteSecrets], which lets them correctly identify payments. | ||
| * | ||
| * When sending a payment, we must always send the [primarySecret]. | ||
| * When receiving payments, we must check if the received contact_secret matches either the [primarySecret] | ||
| * or any of the [additionalRemoteSecrets]. | ||
| */ | ||
| data class ContactSecrets(val primarySecret: ByteVector32, val additionalRemoteSecrets: Set<ByteVector32>) { | ||
| /** | ||
| * This function should be used when we attribute an incoming payment to an existing contact. | ||
| * This can be necessary when: | ||
| * - our contact added us without using the contact_secret we initially sent them | ||
| * - our contact is using a different wallet from the one(s) we have already stored | ||
| */ | ||
| fun addRemoteSecret(remoteSecret: ByteVector32): ContactSecrets { | ||
| return this.copy(additionalRemoteSecrets = additionalRemoteSecrets + remoteSecret) | ||
| } | ||
| } | ||
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| /** | ||
| * Contacts are trusted people to which we may want to reveal our identity when paying them. | ||
| * We're also able to figure out when incoming payments have been made by one of our contacts. | ||
| * See [bLIP 42](https://github.com/lightning/blips/blob/master/blip-0042.md) for more details. | ||
| */ | ||
| object Contacts { | ||
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| /** | ||
| * We derive our contact secret deterministically based on our offer and our contact's offer. | ||
| * This provides a few interesting properties: | ||
| * - if we remove a contact and re-add it using the same offer, we will generate the same contact secret | ||
| * - if our contact is using the same deterministic algorithm with a single static offer, they will also generate the same contact secret | ||
| * | ||
| * Note that this function must only be used when adding a contact that hasn't paid us before. | ||
| * If we're adding a contact that paid us before, we must use the contact_secret they sent us, | ||
| * which ensures that when we pay them, they'll be able to know it was coming from us (see | ||
| * [fromRemoteSecret]). | ||
| */ | ||
| fun computeContactSecret(ourOffer: OfferTypes.OfferAndKey, theirOffer: OfferTypes.Offer): ContactSecrets { | ||
| // If their offer doesn't contain an issuerId, it must contain blinded paths. | ||
| val offerNodeId = theirOffer.issuerId ?: theirOffer.paths?.first()?.nodeId!! | ||
| val ecdh = offerNodeId.times(ourOffer.privateKey) | ||
| val primarySecret = Crypto.sha256("blip42_contact_secret".toByteArray() + ecdh.value.toByteArray()).byteVector32() | ||
| return ContactSecrets(primarySecret, setOf()) | ||
| } | ||
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| /** | ||
| * When adding a contact from which we've received a payment, we must use the contact_secret | ||
| * they sent us: this ensures that they'll be able to identify payments coming from us. | ||
| */ | ||
| fun fromRemoteSecret(remoteSecret: ByteVector32): ContactSecrets = ContactSecrets(remoteSecret, setOf()) | ||
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| } |
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