Private Zaps

This adds private zaps, which have messages and authors encrypted to
the target. Keys are deterministically generated so that both the
receiver and sender can decrypt.

Changelog-Added: Private Zaps

damus/Nostr/NostrEvent.swift

@@ -157,7 +157,7 @@ class NostrEvent: Codable, Identifiable, CustomStringConvertible, Equatable, Has
             pubkey = refkey.ref_id
         }
 
-        let dec = decrypt_dm(key, pubkey: pubkey, content: self.content)
+        let dec = decrypt_dm(key, pubkey: pubkey, content: self.content, encoding: .base64)
         self.decrypted_content = dec
 
         return dec
@@ -577,25 +577,115 @@ func zap_target_to_tags(_ target: ZapTarget) -> [[String]] {
     }
 }
 
-func make_zap_request_event(pubkey: String, privkey: String, content: String, relays: [RelayDescriptor], target: ZapTarget, is_anon: Bool) -> NostrEvent {
+func make_private_zap_request_event(identity: FullKeypair, enc_key: FullKeypair, target: ZapTarget, message: String) -> String? {
+    // target tags must be the same as zap request target tags
+    let tags = zap_target_to_tags(target)
+    
+    let note = NostrEvent(content: message, pubkey: identity.pubkey, kind: 9733, tags: tags)
+    note.id = calculate_event_id(ev: note)
+    note.sig = sign_event(privkey: identity.privkey, ev: note)
+    
+    guard let note_json = encode_json(note) else {
+        return nil
+    }
+    return encrypt_message(message: note_json, privkey: enc_key.privkey, to_pk: target.pubkey, encoding: .bech32)
+}
+
+func decrypt_private_zap(our_privkey: String, zapreq: NostrEvent, target: ZapTarget) -> NostrEvent? {
+    guard let anon_tag = zapreq.tags.first(where: { t in t.count >= 2 && t[0] == "anon" }) else {
+        return nil
+    }
+    
+    let enc_note = anon_tag[1]
+    
+    var note = decrypt_note(our_privkey: our_privkey, their_pubkey: zapreq.pubkey, enc_note: enc_note, encoding: .bech32)
+    
+    // check to see if the private note was from us
+    if note == nil {
+        guard let our_private_keypair = generate_private_keypair(our_privkey: our_privkey, id: target.id, created_at: zapreq.created_at) else{
+            return nil
+        }
+        // use our private keypair and their pubkey to get the shared secret
+        note = decrypt_note(our_privkey: our_private_keypair.privkey, their_pubkey: target.pubkey, enc_note: enc_note, encoding: .bech32)
+    }
+    
+    guard let note else {
+        return nil
+    }
+        
+    guard note.kind == 9733 else {
+        return nil
+    }
+    
+    let zr_etag = zapreq.referenced_ids.first
+    let note_etag = note.referenced_ids.first
+    
+    guard zr_etag == note_etag else {
+        return nil
+    }
+    
+    let zr_ptag = zapreq.referenced_pubkeys.first
+    let note_ptag = note.referenced_pubkeys.first
+    
+    guard let zr_ptag, let note_ptag, zr_ptag == note_ptag else {
+        return nil
+    }
+    
+    guard validate_event(ev: note) == .ok else {
+        return nil
+    }
+    
+    return note
+}
+
+func generate_private_keypair(our_privkey: String, id: String, created_at: Int64) -> FullKeypair? {
+    let to_hash = our_privkey + id + String(created_at)
+    guard let dat = to_hash.data(using: .utf8) else {
+        return nil
+    }
+    let privkey_bytes = sha256(dat)
+    let privkey = hex_encode(privkey_bytes)
+    guard let pubkey = privkey_to_pubkey(privkey: privkey) else {
+        return nil
+    }
+    
+    return FullKeypair(pubkey: pubkey, privkey: privkey)
+}
+
+func make_zap_request_event(keypair: FullKeypair, content: String, relays: [RelayDescriptor], target: ZapTarget, zap_type: ZapType) -> NostrEvent? {
     var tags = zap_target_to_tags(target)
     var relay_tag = ["relays"]
     relay_tag.append(contentsOf: relays.map { $0.url.absoluteString })
     tags.append(relay_tag)
     
-    var priv = privkey
-    var pub = pubkey
+    var kp = keypair
     
-    if is_anon {
+    let now = Int64(Date().timeIntervalSince1970)
+    
+    var message = content
+    switch zap_type {
+    case .pub:
+        break
+    case .non_zap:
+        break
+    case .anon:
         tags.append(["anon"])
-        let kp = generate_new_keypair()
-        pub = kp.pubkey
-        priv = kp.privkey!
+        kp = generate_new_keypair().to_full()!
+    case .priv:
+        guard let priv_kp = generate_private_keypair(our_privkey: keypair.privkey, id: target.id, created_at: now) else {
+            return nil
+        }
+        kp = priv_kp
+        guard let privreq = make_private_zap_request_event(identity: keypair, enc_key: kp, target: target, message: message) else {
+            return nil
+        }
+        tags.append(["anon", privreq])
+        message = ""
     }
     
-    let ev = NostrEvent(content: content, pubkey: pub, kind: 9734, tags: tags)
+    let ev = NostrEvent(content: message, pubkey: kp.pubkey, kind: 9734, tags: tags, createdAt: now)
     ev.id = calculate_event_id(ev: ev)
-    ev.sig = sign_event(privkey: priv, ev: ev)
+    ev.sig = sign_event(privkey: kp.privkey, ev: ev)
     return ev
 }
 
@@ -625,14 +715,14 @@ func event_to_json(ev: NostrEvent) -> String {
     return str
 }
 
-func decrypt_dm(_ privkey: String?, pubkey: String, content: String) -> String? {
+func decrypt_dm(_ privkey: String?, pubkey: String, content: String, encoding: EncEncoding) -> String? {
     guard let privkey = privkey else {
         return nil
     }
     guard let shared_sec = get_shared_secret(privkey: privkey, pubkey: pubkey) else {
         return nil
     }
-    guard let dat = decode_dm_base64(content) else {
+    guard let dat = (encoding == .base64 ? decode_dm_base64(content) : decode_dm_bech32(content)) else {
         return nil
     }
     guard let dat = aes_decrypt(data: dat.content, iv: dat.iv, shared_sec: shared_sec) else {
@@ -641,6 +731,13 @@ func decrypt_dm(_ privkey: String?, pubkey: String, content: String) -> String?
     return String(data: dat, encoding: .utf8)
 }
 
+func decrypt_note(our_privkey: String, their_pubkey: String, enc_note: String, encoding: EncEncoding) -> NostrEvent? {
+    guard let dec = decrypt_dm(our_privkey, pubkey: their_pubkey, content: enc_note, encoding: encoding) else {
+        return nil
+    }
+    
+    return decode_nostr_event_json(json: dec)
+}
 
 func get_shared_secret(privkey: String, pubkey: String) -> [UInt8]? {
     guard let privkey_bytes = try? privkey.bytes else {
@@ -686,6 +783,39 @@ struct DirectMessageBase64 {
     let iv: [UInt8]
 }
 
+
+
+func encode_dm_bech32(content: [UInt8], iv: [UInt8]) -> String {
+    let content_bech32 = bech32_encode(hrp: "pzap", content)
+    let iv_bech32 = bech32_encode(hrp: "iv", iv)
+    return content_bech32 + "_" + iv_bech32
+}
+
+func decode_dm_bech32(_ all: String) -> DirectMessageBase64? {
+    let parts = all.split(separator: "_")
+    guard parts.count == 2 else {
+        return nil
+    }
+    
+    let content_bech32 = String(parts[0])
+    let iv_bech32 = String(parts[1])
+    
+    guard let content_tup = try? bech32_decode(content_bech32) else {
+        return nil
+    }
+    guard let iv_tup = try? bech32_decode(iv_bech32) else {
+        return nil
+    }
+    guard content_tup.hrp == "pzap" else {
+        return nil
+    }
+    guard iv_tup.hrp == "iv" else {
+        return nil
+    }
+    
+    return DirectMessageBase64(content: content_tup.data.bytes, iv: iv_tup.data.bytes)
+}
+
 func encode_dm_base64(content: [UInt8], iv: [UInt8]) -> String {
     let content_b64 = base64_encode(content)
     let iv_b64 = base64_encode(iv)