Create only one event when sending DM to self

Normally, the system creates two identical events: one encrypted to the
sender and one to the recipient.  If those are the same (i.e. you send a
message to yourself), this creates two identical messages.

The gift-wraps already give the two different events different pubkeys,
created_at times, IDs and tags, so there should be no way to associate
them with each other.  Therefore, this change should not allow attackers
to see that a message is sent to oneself by looking for a matching one.

1 files changed, 21 insertions, 14 deletions

diff --git a/src/lib/nip17.ts b/src/lib/nip17.ts
index 9a6d01f6..b8352d1e 100644
--- a/src/lib/nip17.ts
+++ b/src/lib/nip17.ts
@@ -313,6 +313,19 @@ const publishToPreferred = async (event: object, pubkey: string, expiryEnabled:
     }
 }
 
+const createAndPublishMessageEvent = async (sk: Uint8Array, message: string, userPK: string, recipientPK: string, eventFor: string, expiryDays?: number) => {
+    let event;
+    if (sk === null) { // Use NIP-07 extension
+        event = await createNIP17MessageNIP07(
+            message, userPK, recipientPK, eventFor, expiryDays);
+    } else {
+        event1 = createNIP17MessageSK(
+            message, sk, recipientPK, eventFor, expiryDays);
+    }
+
+    return publishToPreferred(event, eventFor, expiryDays != null);
+}
+
 // Sends a NIP-17 message from `user` to `recipient`.
 // If expiryDays is set, messages will expire after that many days.
 export const send = async (message: string, user: object, recipient: object, expiryDays?: number) => {
@@ -322,20 +335,14 @@ export const send = async (message: string, user: object, recipient: object, exp
     // Store sk for auth handler
     currentSk = sk;
 
-    if (sk === null) {
-        // Use NIP-07 extension
-        event1 = await createNIP17MessageNIP07(
-            message, user.pubkey, recipient.pubkey, recipient.pubkey, expiryDays);
-        event2 = await createNIP17MessageNIP07(
-            message, user.pubkey, recipient.pubkey, user.pubkey, expiryDays);
+    if (user.pubkey === recipient.pubkey) {
+        return createAndPublishMessageEvent(
+            sk, message, user.pubkey, recipient.pubkey, user.pubkey, expiryDays);
     } else {
-        event1 = createNIP17MessageSK(
-            message, sk, recipient.pubkey, recipient.pubkey, expiryDays);
-        event2 = createNIP17MessageSK(
-            message, sk, recipient.pubkey, user.pubkey, expiryDays);
+        const p1 = createAndPublishMessageEvent(
+            sk, message, user.pubkey, recipient.pubkey, recipient.pubkey, expiryDays);
+        const p2 = createAndPublishMessageEvent(
+            sk, message, user.pubkey, recipient.pubkey, user.pubkey, expiryDays);
+        return Promise.all([p1, p2]);
     }
-
-    const p1 = publishToPreferred(event1, recipient.pubkey, expiryDays != null);
-    const p2 = publishToPreferred(event2, user.pubkey, expiryDays != null);
-    return Promise.all([p1, p2]);
 }