allow platform-specific NIP-44 decryption

README.md

@@ -14,7 +14,7 @@ async window.nostr.signEvent(event): Event // returns the full event object sign
 async window.nostr.nip04.encrypt(pubkey, plaintext): string // returns ciphertext+iv as specified in nip04
 async window.nostr.nip04.decrypt(pubkey, ciphertext): string // takes ciphertext+iv as specified in nip04
 async window.nostr.nip44.encrypt(pubkey, plaintext): string // takes pubkey, plaintext, returns ciphertext as specified in nip-44
-async window.nostr.nip44.decrypt(pubkey, ciphertext): string // takes pubkey, ciphertext, returns plaintext as specified in nip-44
+async window.nostr.nip44.decrypt(pubkey, ciphertext, options?: {platforms?: string[]}): string // takes pubkey, ciphertext, and optional platforms; returns plaintext as specified in nip-44
 ```
 
 This extension is Chromium-only. For a maintained Firefox fork, see [nos2x-fox](https://diegogurpegui.com/nos2x-fox/).

extension/background.js

@@ -125,10 +125,16 @@ async function handleContentScriptMessage({type, params, host}) {
     // do the operation before asking (because we'll show the encryption/decryption results in the popup
     const finalResult = await performOperation(type, params)
 
+    if (finalResult?.error?.code === 'nip44-decrypt-guard') {
+      releasePromptMutex()
+      return {error: {message: finalResult.error.message}}
+    }
+
     let allowed = await getPermissionStatus(
       host,
       type,
-      type === 'signEvent' ? params.event : undefined
+      type === 'signEvent' ? params.event : undefined,
+      type === 'nip44.decrypt' ? params.platforms : undefined
     )
 
     if (allowed === true) {
@@ -182,11 +188,57 @@ async function handleContentScriptMessage({type, params, host}) {
       }
     }
 
+    if (
+      type === 'nip44.decrypt' &&
+      params.platforms &&
+      typeof finalResult === 'string'
+    ) {
+      try {
+        assertDecryptedMatchesPlatforms(finalResult, params.platforms)
+      } catch (err) {
+        return {error: {message: err.message}}
+      }
+    }
+
     // the call was authorized, so we just return the result we had from before
     return finalResult
   }
 }
 
+function assertDecryptedMatchesPlatforms(plaintext, platforms) {
+  const mismatch = new Error(
+    'website is trying to decrypt a message from a different platform'
+  )
+  let parsed
+  try {
+    parsed = JSON.parse(plaintext)
+  } catch (_) {
+    throw mismatch
+  }
+  if (
+    typeof parsed !== 'object' ||
+    parsed === null ||
+    Array.isArray(parsed) ||
+    !Object.prototype.hasOwnProperty.call(parsed, 'tags') ||
+    !Array.isArray(parsed.tags)
+  ) {
+    throw mismatch
+  }
+  if (
+    !parsed.tags.every(
+      tag => Array.isArray(tag) && tag.every(item => typeof item === 'string')
+    )
+  ) {
+    throw mismatch
+  }
+  let matches = parsed.tags.some(
+    tag =>
+      tag[0] === 'platforms' &&
+      tag.slice(1).some(item => platforms.includes(item))
+  )
+  if (!matches) throw mismatch
+}
+
 async function performOperation(type, params) {
   let results = await browser.storage.local.get('private_key')
   if (!results || !results.private_key) {
@@ -220,9 +272,37 @@ async function performOperation(type, params) {
         return nip44.v2.encrypt(plaintext, key)
       }
       case 'nip44.decrypt': {
-        const {peer, ciphertext} = params
+        const {peer, ciphertext, platforms} = params
+        if (platforms !== undefined) {
+          if (
+            !Array.isArray(platforms) ||
+            !platforms.every(p => typeof p === 'string')
+          ) {
+            return {
+              error: {
+                message: 'platforms must be an array of strings',
+                code: 'nip44-decrypt-guard'
+              }
+            }
+          }
+          if (platforms.length === 0) {
+            return {
+              error: {
+                message: 'platforms must not be empty',
+                code: 'nip44-decrypt-guard'
+              }
+            }
+          }
+          if (platforms.length > 20 || platforms.reduce((acc, p) => acc + p.length, 0) > 1000) {
+            return {
+              error: {
+                message: 'platforms must be less than 20 and the total length of the platforms must be less than 1000',
+                code: 'nip44-decrypt-guard'
+              }
+            }
+          }
+        }
         const key = getSharedSecret(sk, peer)
-
         return nip44.v2.decrypt(ciphertext, key)
       }
     }

extension/common.js

@@ -23,7 +23,32 @@ function matchConditions(conditions, event) {
   return true
 }
 
-export async function getPermissionStatus(host, type, event) {
+function matchDecryptPlatforms(conditions, platforms) {
+  if (conditions?.platforms) {
+    if (!platforms || !platforms.length) return false
+    return platforms.every(platform =>
+      conditions.platforms.includes(platform)
+    )
+  }
+
+  return true
+}
+
+export function getPermissionName(type, params) {
+  if (type === 'nip44.decrypt') {
+    let platforms = params?.platforms
+    if (Array.isArray(platforms) && platforms.length > 0) {
+      return `decrypt events for ${
+        platforms.length === 1 ? 'platform' : 'platforms'
+      }: ${platforms.map(platform => JSON.stringify(platform)).join(', ')}`
+    }
+    return 'decrypt all of your messages'
+  }
+
+  return PERMISSION_NAMES[type]
+}
+
+export async function getPermissionStatus(host, type, event, platforms) {
   let {policies} = await browser.storage.local.get('policies')
 
   let answers = [true, false]
@@ -40,6 +65,12 @@ export async function getPermissionStatus(host, type, event) {
           // or it will end up returning undefined at the end
           continue
         }
+      } else if (type === 'nip44.decrypt') {
+        if (matchDecryptPlatforms(conditions, platforms)) {
+          return accept
+        } else {
+          continue
+        }
       } else {
         return accept // may be true or false
       }
@@ -64,6 +95,18 @@ export async function updatePermission(host, type, accept, conditions) {
           conditions.kinds[kind] = true
         })
       }
+      if (existingConditions.platforms && conditions.platforms) {
+        existingConditions.platforms.forEach(platform => {
+          if (!conditions.platforms.includes(platform)) {
+            conditions.platforms.push(platform)
+          }
+        })
+        if (conditions.platforms.length > 50) {
+          // storing up to 50 platforms is more than enough
+          console.warn('platforms list is too long, truncating to 50')
+          conditions.platforms = conditions.platforms.slice(-50)
+        }
+      }
     }
   }
 

extension/nostr-provider.js

@@ -35,8 +35,8 @@ window.nostr = {
       return window.nostr._call('nip44.encrypt', {peer, plaintext})
     },
 
-    async decrypt(peer, ciphertext) {
-      return window.nostr._call('nip44.decrypt', {peer, ciphertext})
+    async decrypt(peer, ciphertext, options) {
+      return window.nostr._call('nip44.decrypt', {peer, ciphertext, platforms: options?.platforms})
     }
   },
 

extension/options.jsx

@@ -329,7 +329,9 @@ function Options() {
                       <td>
                         {conditions.kinds
                           ? `kinds: ${Object.keys(conditions.kinds).join(', ')}`
-                          : 'always'}
+                          : conditions.platforms
+                            ? `platforms: ${conditions.platforms.map(platform => JSON.stringify(platform)).join(', ')}`
+                            : 'always'}
                       </td>
                       <td>
                         {new Date(created_at * 1000)

extension/prompt.jsx

@@ -2,7 +2,7 @@ import browser from 'webextension-polyfill'
 import {createRoot} from 'react-dom/client'
 import React from 'react'
 
-import {PERMISSION_NAMES} from './common'
+import {getPermissionName} from './common'
 
 function Prompt() {
   let qs = new URLSearchParams(location.search)
@@ -19,13 +19,22 @@ function Prompt() {
     params = null
   }
 
+  let platforms =
+    type === 'nip44.decrypt' && Array.isArray(params?.platforms)
+      ? params.platforms
+      : null
+  let platformConditions = platforms?.length
+    ? {platforms}
+    : null
+
   return (
     <>
       <b style={{display: 'block', textAlign: 'center', fontSize: '200%'}}>
         {host}
       </b>{' '}
       <p style={{margin: 0}}>
-        is requesting your permission to <b>{PERMISSION_NAMES[type]}:</b>
+        is requesting your permission to{' '}
+        <b>{getPermissionName(type, params)}:</b>
       </p>
       {params && (
         <div style={{width: '100%', maxHeight: '200px', overflowY: 'scroll'}}>
@@ -63,7 +72,7 @@ function Prompt() {
             gap: '0.5rem'
           }}
         >
-          {event?.kind === undefined && (
+          {event?.kind === undefined && !platformConditions && (
             <button
               style={{marginTop: '5px'}}
               onClick={authorizeHandler(
@@ -85,6 +94,15 @@ function Prompt() {
               authorize kind {event.kind} forever
             </button>
           )}
+          {platformConditions && (
+            <button
+              style={{marginTop: '5px'}}
+              onClick={authorizeHandler(true, platformConditions)}
+            >
+              authorize {platforms.length === 1 ? 'platform' : 'platforms'}{' '}
+              {platforms.map(platform => JSON.stringify(platform)).join(', ')} forever
+            </button>
+          )}
           <button style={{marginTop: '5px'}} onClick={authorizeHandler(true)}>
             authorize just this
           </button>
@@ -107,6 +125,14 @@ function Prompt() {
             >
               reject kind {event.kind} forever
             </button>
+          ) : platformConditions ? (
+            <button
+              style={{marginTop: '5px'}}
+              onClick={authorizeHandler(false, platformConditions)}
+            >
+              reject {platforms.length === 1 ? 'platform' : 'platforms'}{' '}
+              {platforms.map(platform => JSON.stringify(platform)).join(', ')} forever
+            </button>
           ) : (
             <button
               style={{marginTop: '5px'}}