From 3e4900606624220e6c112a5438698b03ee3c3943 Mon Sep 17 00:00:00 2001
From: Adrien Hopkins <adrien.p.hopkins@gmail.com>
Date: Thu, 13 Nov 2025 11:16:25 -0500
Subject: Add expiration timestamps to kind 13 seals

In case these leak, they will expire automatically.  Currently, they use
the same method as the gift wrap expirations: expiration + 2 days after
the creation timestamp.
---
 src/lib/nip17.ts | 36 ++++++++++++++++++++++++------------
 1 file changed, 24 insertions(+), 12 deletions(-)

diff --git a/src/lib/nip17.ts b/src/lib/nip17.ts
index 9dd59f6f..cb9a0573 100644
--- a/src/lib/nip17.ts
+++ b/src/lib/nip17.ts
@@ -10,9 +10,12 @@ const randomTimestamp = () => Math.floor(
 // If wrapPK is specified and different than receiverPK,
 // the message will be gift-wrapped to wrapPK
 // but the rumour will be sent to receiverPK.
+// If expiryDays is specified, the message will expire in that many days,
+// plus a random amount from 0 to 2 for security.
+// (expiration time = random creation time + expiryDays + 2 days)
 export const createNIP17MessageSK = (text: string, senderSK: Uint8Array, receiverPK: string, wrapPK: string = null, expiryDays: number = null) => {
     const rumour = createRumour(text, getPublicKey(senderSK), receiverPK);
-    const sealed = sealRumourSK(rumour, senderSK, wrapPK || receiverPK);
+    const sealed = sealRumourSK(rumour, senderSK, wrapPK || receiverPK, expiryDays);
     return giftWrap(sealed, wrapPK || receiverPK, expiryDays);
 }
 
@@ -25,7 +28,7 @@ export const createNIP17MessageSK = (text: string, senderSK: Uint8Array, receive
 // (expiration time = random creation time + expiryDays + 2 days)
 export const createNIP17MessageNIP07 = async (text: string, senderPK: string, receiverPK: string, wrapPK: string = null, expiryDays: number = null) => {
     const rumour = createRumour(text, senderPK, receiverPK);
-    const sealed = await sealRumourNip07(rumour, wrapPK || receiverPK);
+    const sealed = await sealRumourNip07(rumour, wrapPK || receiverPK, expiryDays);
     return giftWrap(sealed, wrapPK || receiverPK, expiryDays);
 }
 
@@ -41,32 +44,42 @@ const createRumour = (text: string, senderPK: string, receiverPK: string) => {
     return rumour;
 }
 
-const sealRumourSK = (rumour: object, senderSK: Uint8Array, receiverPK: string) => {
+const sealRumourSK = (rumour: object, senderSK: Uint8Array, receiverPK: string, expiryDays: number = null) => {
     const senderSKString = bytesToHex(senderSK);
     const conversationKey = u.getConversationKey(senderSKString, receiverPK);
     const encryptedRumour = encrypt(JSON.stringify(rumour), conversationKey);
 
+    const created = randomTimestamp();
     const sealEvent = {
         kind: 13, // seal
-        created_at: randomTimestamp(),
+        created_at: created,
         tags: [],
         pubkey: getPublicKey(senderSK),
         content: encryptedRumour
     }
+    if (expiryDays != null) {
+        const expiration = created + (expiryDays + 2) * 86400;
+        sealEvent.tags.push(["expiration", expiration.toString()]);
+    }
 
     return finalizeEvent(sealEvent, senderSK);
 }
 
-const sealRumourNip07 = async (rumour: object, receiverPK: string) => {
+const sealRumourNip07 = async (rumour: object, receiverPK: string, expiryDays: number = null) => {
     const encryptedRumour = await window.nostr.nip44.encrypt(
         receiverPK, JSON.stringify(rumour));
 
+    const created = randomTimestamp();
     const sealEvent = {
         kind: 13, // seal
-        created_at: randomTimestamp(),
+        created_at: created,
         tags: [],
         content: encryptedRumour
     }
+    if (expiryDays != null) {
+        const expiration = created + (expiryDays + 2) * 86400;
+        sealEvent.tags.push(["expiration", expiration.toString()]);
+    }
 
     return window.nostr.signEvent(sealEvent);
 }
@@ -77,19 +90,18 @@ const giftWrap = (event: object, receiverPK: string, expiryDays: number = null)
     const conversationKey = u.getConversationKey(secretKey, receiverPK);
     const encryptedEvent = encrypt(JSON.stringify(event), conversationKey);
     const created = randomTimestamp();
-    const tags = [["p", receiverPK]];
-    if (expiryDays != null) {
-        const expiration = created + (expiryDays + 2) * 86400;
-        tags.push(["expiration", expiration.toString()]);
-    }
 
     const giftWrapEvent = {
         kind: 1059, // gift wrap
         created_at: created,
-        tags: tags,
+        tags: [["p", receiverPK]],
         pubkey: getPublicKey(secretKey),
         content: encryptedEvent
     }
+    if (expiryDays != null) {
+        const expiration = created + (expiryDays + 2) * 86400;
+        giftWrapEvent.tags.push(["expiration", expiration.toString()]);
+    }
 
     return finalizeEvent(giftWrapEvent, secretKey);
 }
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