diff --git a/js/signal_protocol_store.js b/js/signal_protocol_store.js
index 26cbd108..9ef385b9 100644
--- a/js/signal_protocol_store.js
+++ b/js/signal_protocol_store.js
@@ -250,6 +250,19 @@
             });
 
         },
+        isTrustedIdentity: function(identifier, publicKey) {
+            if (identifier === null || identifier === undefined) {
+                throw new Error("Tried to get identity key for undefined/null key");
+            }
+            var number = textsecure.utils.unencodeNumber(identifier)[0];
+            return new Promise(function(resolve) {
+                var identityKey = new IdentityKey({id: number});
+                identityKey.fetch().always(function() {
+                    var oldpublicKey = identityKey.get('publicKey');
+                    resolve(!oldpublicKey || equalArrayBuffers(oldpublicKey, publicKey));
+                });
+            });
+        },
         loadIdentityKey: function(identifier) {
             if (identifier === null || identifier === undefined) {
                 throw new Error("Tried to get identity key for undefined/null key");
diff --git a/libtextsecure/test/in_memory_signal_protocol_store.js b/libtextsecure/test/in_memory_signal_protocol_store.js
index 84039ac9..8cfe2561 100644
--- a/libtextsecure/test/in_memory_signal_protocol_store.js
+++ b/libtextsecure/test/in_memory_signal_protocol_store.js
@@ -29,6 +29,19 @@ SignalProtocolStore.prototype = {
 		delete this.store[key];
 	},
 
+	isTrustedIdentity: function(identifier, identityKey) {
+		if (identifier === null || identifier === undefined) {
+			throw new error("tried to check identity key for undefined/null key");
+		}
+		if (!(identityKey instanceof ArrayBuffer)) {
+			throw new error("Expected identityKey to be an ArrayBuffer");
+		}
+		var trusted = this.get('identityKey' + identifier);
+		if (trusted === undefined) {
+			return Promise.resolve(true);
+		}
+		return Promise.resolve(identityKey === trusted);
+	},
 	loadIdentityKey: function(identifier) {
 		if (identifier === null || identifier === undefined)
 			throw new Error("Tried to get identity key for undefined/null key");