Add GROUP destination support with symmetric key encryption

src/destination.js

@@ -1,6 +1,7 @@
 import EventEmitter from "./utils/events.js";
 import Constants from "./constants.js";
 import Cryptography from "./cryptography.js";
+import Fernet from "./fernet.js";
 import Packet from "./packet.js";
 import Transport from "./transport.js";
 import Identity from "./identity.js";
@@ -13,9 +14,9 @@ import Link from "./link.js";
  */
 class Destination extends EventEmitter {
 
-    // // constants
+    // constants
     static SINGLE = 0x00;
-    // static GROUP = 0x01;
+    static GROUP = 0x01;
     static PLAIN = 0x02;
     static LINK = 0x03;
     // static DESTINATION_TYPES = [this.SINGLE, this.GROUP, this.PLAIN, this.LINK];
@@ -87,6 +88,42 @@ class Destination extends EventEmitter {
         return Destination.hash(identity, appName, ...aspects);
     }
 
+    /**
+     * For a GROUP type destination, creates a new symmetric key.
+     * @returns {Buffer} the generated key
+     */
+    createKeys() {
+        if(this.type !== Destination.GROUP){
+            throw new Error("Only GROUP destinations can create symmetric keys");
+        }
+        this.privateKeyBytes = Fernet.generateKey();
+        this.fernet = new Fernet(this.privateKeyBytes);
+        return this.privateKeyBytes;
+    }
+
+    /**
+     * For a GROUP type destination, loads a symmetric private key.
+     * @param key a 32-byte Buffer containing the symmetric key
+     */
+    loadPrivateKey(key) {
+        if(this.type !== Destination.GROUP){
+            throw new Error("Only GROUP destinations can hold symmetric keys");
+        }
+        this.privateKeyBytes = key;
+        this.fernet = new Fernet(key);
+    }
+
+    /**
+     * For a GROUP type destination, returns the symmetric private key.
+     * @returns {Buffer}
+     */
+    getPrivateKey() {
+        if(this.type !== Destination.GROUP){
+            throw new Error("Only GROUP destinations can hold symmetric keys");
+        }
+        return this.privateKeyBytes;
+    }
+
     /**
      * Encrypts data for this Destination.
      * @param data the data to encrypt
@@ -105,6 +142,14 @@ class Destination extends EventEmitter {
             return this.identity.encrypt(data);
         }
 
+        // handle group destination type with symmetric key
+        if(this.type === Destination.GROUP){
+            if(this.fernet != null){
+                return this.fernet.encrypt(data);
+            }
+            throw new Error("No private key held by GROUP destination. Did you create or load one?");
+        }
+
         throw new Error("Not Implemented");
 
     }
@@ -127,6 +172,19 @@ class Destination extends EventEmitter {
             return this.identity.decrypt(data);
         }
 
+        // handle group destination type with symmetric key
+        if(this.type === Destination.GROUP){
+            if(this.fernet != null){
+                try {
+                    return this.fernet.decrypt(data);
+                } catch(e) {
+                    console.log("The GROUP destination could not decrypt data", e);
+                    return null;
+                }
+            }
+            throw new Error("No private key held by GROUP destination. Did you create or load one?");
+        }
+
         throw new Error("Not Implemented");
 
     }
@@ -151,6 +209,16 @@ class Destination extends EventEmitter {
 
         // handle incoming data
         if(packet.packetType === Packet.DATA){
+
+            // fire packet callback if registered
+            if(this.packetCallback != null){
+                try {
+                    this.packetCallback(plaintext, packet);
+                } catch(e) {
+                    console.log("Error while executing packet callback", e);
+                }
+            }
+
             this.emit("packet", {
                 packet: packet,
                 data: plaintext,
@@ -180,6 +248,14 @@ class Destination extends EventEmitter {
 
     }
 
+    /**
+     * Registers a function to be called when a packet has been received by this destination.
+     * @param callback a function with the signature callback(data, packet)
+     */
+    setPacketCallback(callback) {
+        this.packetCallback = callback;
+    }
+
     /**
      * Send an announce on all interfaces with the provided app data.
      * @param appDataBytes