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Support multiple profiles for LUD-05 #216

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5 changes: 4 additions & 1 deletion 05.md
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Expand Up @@ -11,13 +11,16 @@ LUD-05: BIP32-based seed generation for auth protocol.
2. `LN SERVICE` full domain name is extracted from login `LNURL` and then hashed using `hmacSha256(hashingKey, full service domain name)`. Full domain name here means FQDN with last full-stop (aka "point") omitted (Example: for `https://x.y.z.com/...` it would be `x.y.z.com`).
3. First 16 bytes are taken from resulting hash and then turned into a sequence of 4 `Long` values which are in turn used to derive a service-specific `linkingKey` using `m/138'/<long1>/<long2>/<long3>/<long4>` path, a Scala example:

If you want to support multiple profiles, you can use a `profileIndex` in the hashing key derivation path: `m/138'/<profileIndex>`, incrementing the counter for each new profile.

```Scala
import fr.acinq.bitcoin.crypto
import fr.acinq.bitcoin.Protocol
import java.io.ByteArrayInputStream
import fr.acinq.bitcoin.DeterministicWallet._
val domainName = "site.com"
val hashingPrivKey = derivePrivateKey(walletMasterKey, hardened(138L) :: 0L :: Nil)
val profileIndex = 0L
val hashingPrivKey = derivePrivateKey(walletMasterKey, hardened(138L) :: profileIndex :: Nil)
val derivationMaterial = hmac256(key = hashingPrivKey.toBin, message = domainName)
val stream = new ByteArrayInputStream(derivationMaterial.slice(0, 16).toArray)
val pathSuffix = Vector.fill(4)(Protocol.uint32(stream, ByteOrder.BIG_ENDIAN)) // each uint32 call consumes next 4 bytes
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