bloom filter specs.

17.md

@@ -104,14 +104,61 @@ Clients SHOULD publish kind `14` events to the `10050`-listed relays. If that is
 
 A client MAY publish a kind `30010` which means saw messages with a `"d"` tag set to receivers pubkey.
 
-The `.content` field is a base64 encoded string of a bloom filter containing message ids (gift wrapped) saw by receiver. 
+The `.content` field has 4 sections separated by `:`:
+
+1. The number of bits in the bit array,
+2. The number of hash rounds applied.
+3. The Base64 encoded string of a bloom filter containing message ids (gift wrapped) saw by receiver.
+4. The salt encoded in the Base64.
 
 The sender pubkey's client MAY query that specific event to check which messaged in this chat is seen by receiver to enhance user experience.
 
+Bloom filters MUST use `SHA256` functions applied to the concatenation of the key, salt, and index, as demonstrated in the pseudocode below:
+
+```js
+class BloomFilter(size: Int, rounds: Int, buffer: ByteArray, salt: ByteArray) {
+    val bits = BitArray(buffer)
+
+    fun bitIndex(value: ByteArray, index: Byte) {
+        return BigInt(sha256(value || salt || index)) % size
+    }
+
+    fun add(id: HexID) {
+        val value = id.hexToByteArray()
+
+        for (index in 0 until rounds) {
+            bits[bitIndex(value, index)] = true 
+        }
+    }
+
+    fun mightContains(id: HexID): Boolean {
+        val value = id.hexToByteArray()
+
+        for (index in 0 until rounds) {
+            if (!bits[bitIndex(value, index)]) {
+                return false
+            }
+        }
+
+        return true
+    }
+
+    fun encode() {
+        return size + ":" + rounds + ":" + base64Encode(bits.toByteArray()) + ":" + base64Encode(salt) 
+    }
+
+    fun decode(str: String): BloomFilter {
+        val [sizeStr, roundsStr, bufferB64, saltB64] = str.split(":")
+        return BloomFilter(sizeStr.toInt(), roundsStr.toInt(), base64Decode(bufferB64), base64Decode(saltB64))
+    }
+}
+```
+
 Example event:
 
 ```json
 {
+    "pubkey" : "badbdda507572b397852048ea74f2ef3ad92b1aac07c3d4e1dec174e8cdc962a",
     "kind": 30010,
     "created_at": 1738964056,
     "tags": [
@@ -120,10 +167,12 @@ Example event:
             "bd4ae3e67e29964d494172261dc45395c89f6bd2e774642e366127171dfb81f5"
         ]
     ],
-    "content": "AAAAAAAACJEAAAAAAAAAAQAAAAAAAAiRAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAQAAAAAAAAAAAABAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA",
+    "content": "100:10:AAAkAQANcYQFCQoB:hZkZYqqdxcE",
 }
 ```
 
+In this example the pubkey `badbdda507572b397852048ea74f2ef3ad92b1aac07c3d4e1dec174e8cdc962a`, has confirmed that they saw the messages with ids of `ca29c211f1c72d5b6622268ff43d2288ea2b2cb5b9aa196ff9f1704fc914b71b` and `460c25e682fda7832b52d1f22d3d22b3176d972f60dcdc3212ed8c92ef85065c` from pubkey `bd4ae3e67e29964d494172261dc45395c89f6bd2e774642e366127171dfb81f5`.
+
 A client MAY encrypt the `.content` based on [NIP-44](44.md) for more privacy.
 
 ## Relays