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+# NIP-100
+
+## Android Signer Application
+
+`draft` `optional`
+
+This NIP describes a method for 2-way communication between an Android signer and any Nostr client on Android. The Android signer is an Android Application and the client can be a web client or an Android application.
+
+# Usage for Android applications
+
+The Android signer uses Intents and Content Resolvers to communicate between applications.
+
+To be able to use the Android signer in your application you should add this to your AndroidManifest.xml:
+
+```xml
+<queries>
+  <intent>
+    <action android:name="android.intent.action.VIEW" />
+    <category android:name="android.intent.category.BROWSABLE" />
+    <data android:scheme="nostrsigner" />
+  </intent>
+</queries>
+```
+
+Then you can use this function to check if there's a signer application installed:
+
+```kotlin
+fun isExternalSignerInstalled(context: Context): Boolean {
+  val intent =
+    Intent().apply {
+      action = Intent.ACTION_VIEW
+      data = Uri.parse("nostrsigner:")
+    }
+  val infos = context.packageManager.queryIntentActivities(intent, 0)
+  return infos.size > 0
+}
+```
+
+## Using Intents
+
+To get the result back from the Signer Application you should use `registerForActivityResult` or `rememberLauncherForActivityResult` in Kotlin. If you are using another framework check the documentation of your framework or a third party library to get the result.
+
+```kotlin
+val launcher = rememberLauncherForActivityResult(
+    contract = ActivityResultContracts.StartActivityForResult(),
+    onResult = { result ->
+        if (result.resultCode != Activity.RESULT_OK) {
+            Toast.makeText(
+                context,
+                "Sign request rejected",
+                Toast.LENGTH_SHORT
+            ).show()
+        } else {
+            val signature = activityResult.data?.getStringExtra("signature")
+            // Do something with signature ...
+        }
+    }
+)
+```
+
+Create the Intent using the **nostrsigner** scheme:
+
+```kotlin
+val intent = Intent(Intent.ACTION_VIEW, Uri.parse("nostrsigner:$content"))
+```
+
+Set the Signer package name:
+
+```kotlin
+intent.`package` = "com.example.signer"
+```
+
+Send the Intent:
+
+```kotlin
+launcher.launch(intent)
+```
+
+### Methods
+
+- **get_public_key**
+  - params:
+
+    ```kotlin
+    val intent = Intent(Intent.ACTION_VIEW, Uri.parse("nostrsigner:"))
+    intent.`package` = "com.example.signer"
+    intent.putExtra("type", "get_public_key")
+    // You can send some default permissions for the user to authorize for ever
+    val permissions = listOf(
+      Permission(
+          type = "sign_event",
+          kind = 22242
+      ),
+      Permission(
+          type = "nip44_decrypt"
+      )
+    )
+    intent.putExtra("permissions", permissions.toJson())
+    context.startActivity(intent)
+    ```
+  - result:
+    - If the user approved intent it will return the **npub** in the signature field
+
+      ```kotlin
+      val npub = intent.data?.getStringExtra("signature")
+      // The package name of the signer application
+      val packageName = intent.data?.getStringExtra("package")
+      ```
+
+- **sign_event**
+  - params:
+
+    ```kotlin
+    val intent = Intent(Intent.ACTION_VIEW, Uri.parse("nostrsigner:$eventJson"))
+    intent.`package` = "com.example.signer"
+    intent.putExtra("type", "sign_event")
+    // To handle results when not waiting between intents
+    intent.putExtra("id", event.id)
+    // Send the current logged in user npub
+    intent.putExtra("current_user", npub)
+    
+    context.startActivity(intent)
+    ```
+  - result:
+    - If the user approved intent it will return the **signature**, **id** and **event** fields
+
+      ```kotlin
+      val signature = intent.data?.getStringExtra("signature")
+      // The id you sent
+      val id = intent.data?.getStringExtra("id")
+      val signedEventJson = intent.data?.getStringExtra("event")
+      ```
+
+- **nip04_encrypt**
+  - params:
+
+    ```kotlin
+    val intent = Intent(Intent.ACTION_VIEW, Uri.parse("nostrsigner:$plaintext"))
+    intent.`package` = "com.example.signer"
+    intent.putExtra("type", "nip04_encrypt")
+    // to control the result in your application in case you are not waiting the result before sending another intent
+    intent.putExtra("id", "some_id")
+    // Send the current logged in user npub
+    intent.putExtra("current_user", account.keyPair.pubKey.toNpub())
+    // Send the hex pubKey that will be used for encrypting the data
+    intent.putExtra("pubKey", pubKey)
+    
+    context.startActivity(intent)
+    ```
+  - result:
+    - If the user approved intent it will return the **signature** and **id** fields
+
+      ```kotlin
+      val encryptedText = intent.data?.getStringExtra("signature")
+      // the id you sent
+      val id = intent.data?.getStringExtra("id")
+      ```
+
+- **nip44_encrypt**
+  - params:
+
+    ```kotlin
+    val intent = Intent(Intent.ACTION_VIEW, Uri.parse("nostrsigner:$plaintext"))
+    intent.`package` = "com.example.signer"
+    intent.putExtra("type", "nip44_encrypt")
+    // to control the result in your application in case you are not waiting the result before sending another intent
+    intent.putExtra("id", "some_id")
+    // Send the current logged in user npub
+    intent.putExtra("current_user", account.keyPair.pubKey.toNpub())
+    // Send the hex pubKey that will be used for encrypting the data
+    intent.putExtra("pubKey", pubKey)
+    
+    context.startActivity(intent)
+    ```
+  - result:
+    - If the user approved intent it will return the **signature** and **id** fields
+
+      ```kotlin
+      val encryptedText = intent.data?.getStringExtra("signature")
+      // the id you sent
+      val id = intent.data?.getStringExtra("id")
+      ```      
+
+- **nip04_decrypt**
+  - params:
+
+    ```kotlin
+    val intent = Intent(Intent.ACTION_VIEW, Uri.parse("nostrsigner:$encryptedText"))
+    intent.`package` = "com.example.signer"
+    intent.putExtra("type", "nip04_decrypt")
+    // to control the result in your application in case you are not waiting the result before sending another intent
+    intent.putExtra("id", "some_id")
+    // Send the current logged in user npub
+    intent.putExtra("current_user", account.keyPair.pubKey.toNpub())
+    // Send the hex pubKey that will be used for decrypting the data
+    intent.putExtra("pubKey", pubKey)
+    
+    context.startActivity(intent)
+    ```
+  - result:
+    - If the user approved intent it will return the **signature** and **id** fields
+
+      ```kotlin
+      val plainText = intent.data?.getStringExtra("signature")
+      // the id you sent
+      val id = intent.data?.getStringExtra("id")
+      ```      
+
+- **nip44_decrypt**
+  - params:
+
+    ```kotlin
+    val intent = Intent(Intent.ACTION_VIEW, Uri.parse("nostrsigner:$encryptedText"))
+    intent.`package` = "com.example.signer"
+    intent.putExtra("type", "nip04_decrypt")
+    // to control the result in your application in case you are not waiting the result before sending another intent
+    intent.putExtra("id", "some_id")
+    // Send the current logged in user npub
+    intent.putExtra("current_user", account.keyPair.pubKey.toNpub())
+    // Send the hex pubKey that will be used for decrypting the data
+    intent.putExtra("pubKey", pubKey)
+    
+    context.startActivity(intent)
+    ```
+  - result:
+    - If the user approved intent it will return the **signature** and **id** fields
+
+      ```kotlin
+      val plainText = intent.data?.getStringExtra("signature")
+      // the id you sent
+      val id = intent.data?.getStringExtra("id")
+      ```        
+
+- **decrypt_zap_event**
+  - params:
+
+    ```kotlin
+    val intent = Intent(Intent.ACTION_VIEW, Uri.parse("nostrsigner:$eventJson"))
+    intent.`package` = "com.example.signer"
+    intent.putExtra("type", "decrypt_zap_event")
+    // to control the result in your application in case you are not waiting the result before sending another intent
+    intent.putExtra("id", "some_id")
+    // Send the current logged in user npub
+    intent.putExtra("current_user", account.keyPair.pubKey.toNpub())
+    context.startActivity(intent)
+    ```
+  - result:
+    - If the user approved intent it will return the **signature** and **id** fields
+
+      ```kotlin
+      val eventJson = intent.data?.getStringExtra("signature")
+      // the id you sent
+      val id = intent.data?.getStringExtra("id")
+      ```         
+
+## Using Content Resolver
+
+To get the result back from Signer Application you should use contentResolver.query in Kotlin. If you are using another framework check the documentation of your framework or a third party library to get the result.
+
+If the user did not check the "remember my choice" option, the npub is not in Signer Application or the signer type is not recognized the `contentResolver` will return null
+
+For the SIGN_EVENT type Signer Application returns two columns "signature" and "event". The column event is the signed event json
+
+For the other types Signer Application returns the column "signature"
+
+If the user chose to always reject the event, signer application will return the column "rejected" and you should not open signer application
+
+### Methods
+
+- **get_public_key**
+  - params:
+
+    ```kotlin
+    val result = context.contentResolver.query(
+        Uri.parse("content://com.example.signer.GET_PUBLIC_KEY"),
+        listOf("login"),
+        null,
+        null,
+        null
+    )
+    ```
+  - result:
+    - Will return the **npub** in the signature column
+
+      ```kotlin
+        if (result == null) return
+
+        if (result.moveToFirst()) {
+            val index = it.getColumnIndex("signature")
+            if (index < 0) return
+            val npub = it.getString(index)
+        }
+      ```
+
+- **sign_event**
+  - params:
+
+    ```kotlin
+    val result = context.contentResolver.query(
+        Uri.parse("content://com.example.signer.SIGN_EVENT"),
+        listOf("$eventJson", "", "${logged_in_user_npub}"),
+        null,
+        null,
+        null
+    )
+    ```
+  - result:
+    - Will return the **signature** and the **event** columns
+
+      ```kotlin
+        if (result == null) return
+
+        if (result.moveToFirst()) {
+            val index = it.getColumnIndex("signature")
+            val indexJson = it.getColumnIndex("event")
+            val signature = it.getString(index)
+            val eventJson = it.getString(indexJson)
+        }
+      ```
+
+- **nip04_encrypt**
+  - params:
+
+    ```kotlin
+    val result = context.contentResolver.query(
+        Uri.parse("content://com.example.signer.NIP04_ENCRYPT"),
+        listOf("$plainText", "${hex_pub_key}", "${logged_in_user_npub}"),
+        null,
+        null,
+        null
+    )
+    ```
+  - result:
+    - Will return the **signature** column
+
+      ```kotlin
+        if (result == null) return
+
+        if (result.moveToFirst()) {
+            val index = it.getColumnIndex("signature")
+            val encryptedText = it.getString(index)
+        }
+      ```
+
+- **nip44_encrypt**
+  - params:
+
+    ```kotlin
+    val result = context.contentResolver.query(
+        Uri.parse("content://com.example.signer.NIP44_ENCRYPT"),
+        listOf("$plainText", "${hex_pub_key}", "${logged_in_user_npub}"),
+        null,
+        null,
+        null
+    )
+    ```
+  - result:
+    - Will return the **signature** column
+
+      ```kotlin
+        if (result == null) return
+
+        if (result.moveToFirst()) {
+            val index = it.getColumnIndex("signature")
+            val encryptedText = it.getString(index)
+        }
+      ```    
+
+- **nip04_decrypt**
+  - params:
+
+    ```kotlin
+    val result = context.contentResolver.query(
+        Uri.parse("content://com.example.signer.NIP04_DECRYPT"),
+        listOf("$encryptedText", "${hex_pub_key}", "${logged_in_user_npub}"),
+        null,
+        null,
+        null
+    )
+    ```
+  - result:
+    - Will return the **signature** column
+
+      ```kotlin
+        if (result == null) return
+
+        if (result.moveToFirst()) {
+            val index = it.getColumnIndex("signature")
+            val encryptedText = it.getString(index)
+        }
+      ```    
+
+- **nip44_decrypt**
+  - params:
+
+    ```kotlin
+    val result = context.contentResolver.query(
+        Uri.parse("content://com.example.signer.NIP44_DECRYPT"),
+        listOf("$encryptedText", "${hex_pub_key}", "${logged_in_user_npub}"),
+        null,
+        null,
+        null
+    )
+    ```
+  - result:
+    - Will return the **signature** column
+
+      ```kotlin
+        if (result == null) return
+
+        if (result.moveToFirst()) {
+            val index = it.getColumnIndex("signature")
+            val encryptedText = it.getString(index)
+        }
+      ```      
+
+- **decrypt_zap_event**
+  - params:
+
+    ```kotlin
+    val result = context.contentResolver.query(
+        Uri.parse("content://com.example.signer.DECRYPT_ZAP_EVENT"),
+        listOf("$eventJson", "", "${logged_in_user_npub}"),
+        null,
+        null,
+        null
+    )
+    ```
+  - result:
+    - Will return the **signature** column
+
+      ```kotlin
+        if (result == null) return
+
+        if (result.moveToFirst()) {
+            val index = it.getColumnIndex("signature")
+            val eventJson = it.getString(index)
+        }
+      ```    
+
+# Usage for Web Applications
+
+Since web applications can't receive a result from the intent, you should add a modal to paste the signature or the event json or create a callback url.
+
+If you send the callback url parameter, Signer Application will send the result to the url.
+
+If you don't send a callback url, Signer Application will copy the result to the clipboard.
+
+You can configure the `returnType` to be **signature** or **event**.
+
+Android intents and browser urls have limitations, so if you are using the `returnType` of **event** consider using the parameter **compressionType=gzip** that will return "Signer1" + Base64 gzip encoded event json
+
+## Methods
+
+- **get_public_key**
+  - params:
+
+    ```js
+    window.href = `nostrsigner:?compressionType=none&returnType=signature&type=get_public_key&callbackUrl=https://example.com/?event=`;
+    ```
+
+- **sign_event**
+  - params:
+
+    ```js
+    window.href = `nostrsigner:${eventJson}?compressionType=none&returnType=signature&type=sign_event&callbackUrl=https://example.com/?event=`;
+    ``` 
+
+- **nip04_encrypt**
+  - params:
+
+    ```js
+    window.href = `nostrsigner:${plainText}?pubKey=${hex_pub_key}&compressionType=none&returnType=signature&type=nip04_encrypt&callbackUrl=https://example.com/?event=`;
+    ``` 
+
+- **nip44_encrypt**
+  - params:
+
+    ```js
+    window.href = `nostrsigner:${plainText}?pubKey=${hex_pub_key}&compressionType=none&returnType=signature&type=nip44_encrypt&callbackUrl=https://example.com/?event=`;
+    ```   
+
+- **nip04_decrypt**
+  - params:
+
+    ```js
+    window.href = `nostrsigner:${encryptedText}?pubKey=${hex_pub_key}&compressionType=none&returnType=signature&type=nip04_decrypt&callbackUrl=https://example.com/?event=`;
+    ```     
+
+- **nip44_decrypt**
+  - params:
+
+    ```js
+    window.href = `nostrsigner:${encryptedText}?pubKey=${hex_pub_key}&compressionType=none&returnType=signature&type=nip44_decrypt&callbackUrl=https://example.com/?event=`;
+    ```     
+
+- **decrypt_zap_event**
+  - params:
+
+    ```js
+    window.href = `nostrsigner:${eventJson}?compressionType=none&returnType=signature&type=decrypt_zap_event&callbackUrl=https://example.com/?event=`;
+    ```          
+
+## Example
+
+```js
+<!DOCTYPE html>
+<html lang="en">
+<head>
+    <meta charset="UTF-8">
+    <meta name="viewport" content="width=device-width, initial-scale=1.0">
+    <title>Document</title>
+</head>
+<body>
+    <h1>Test</h1>
+       
+    <script>
+        window.onload = function() {
+            var url = new URL(window.location.href);
+            var params = url.searchParams;
+            if (params) {
+                var param1 = params.get("event");
+                if (param1) alert(param1)
+            }
+            let json = {
+                kind: 1,
+                content: "test"
+            }
+            let encodedJson = encodeURIComponent(JSON.stringify(json))
+            var newAnchor = document.createElement("a");
+            newAnchor.href = `nostrsigner:${encodedJson}?compressionType=none&returnType=signature&type=sign_event&callbackUrl=https://example.com/?event=`;
+            newAnchor.textContent = "Open External Signer";
+            document.body.appendChild(newAnchor)
+        }
+    </script>
+</body>
+</html>
+```