From d1a3d73c5f342ea33839343485e6e2b9dd773c83 Mon Sep 17 00:00:00 2001
From: Michelle Linington <michelle@signal.org>
Date: Fri, 28 May 2021 00:33:53 -0700
Subject: [PATCH] Composable access keys

Sender key requires a derived access key that's composed of each
recipients access key xor-ed.
---
 SignalMetadataKit/src/SMKSecretSessionCipher.swift |  1 +
 SignalMetadataKit/src/SMKUDAccessKey.swift         | 13 +++++++++++++
 2 files changed, 14 insertions(+)

diff --git a/SignalMetadataKit/src/SMKSecretSessionCipher.swift b/SignalMetadataKit/src/SMKSecretSessionCipher.swift
index 8266d2c..a01682f 100644
--- a/SignalMetadataKit/src/SMKSecretSessionCipher.swift
+++ b/SignalMetadataKit/src/SMKSecretSessionCipher.swift
@@ -240,6 +240,7 @@ fileprivate extension SMKMessageType {
             udMessageContent,
             for: recipients,
             identityStore: identityStore,
+            sessionStore: sessionStore,
             context: protocolContext ?? NullContext())
 
         return Data(multiRecipientMessage)
diff --git a/SignalMetadataKit/src/SMKUDAccessKey.swift b/SignalMetadataKit/src/SMKUDAccessKey.swift
index 71aa6e9..7495e3d 100644
--- a/SignalMetadataKit/src/SMKUDAccessKey.swift
+++ b/SignalMetadataKit/src/SMKUDAccessKey.swift
@@ -42,6 +42,19 @@ public class SMKUDAccessKey: NSObject {
         self.keyData = Randomness.generateRandomBytes(Int32(SMKUDAccessKey.kUDAccessKeyLength))
     }
 
+    private init(keyData: Data) {
+        self.keyData = keyData
+    }
+
+    /// Used to compose multiple Unidentified-Access-Keys for the multiRecipient endpoint
+    public static func ^(lhs: SMKUDAccessKey, rhs: SMKUDAccessKey) -> SMKUDAccessKey {
+        owsAssert(lhs.keyData.count == SMKUDAccessKey.kUDAccessKeyLength)
+        owsAssert(rhs.keyData.count == SMKUDAccessKey.kUDAccessKeyLength)
+
+        let xoredBytes = zip(lhs.keyData, rhs.keyData).map(^)
+        return .init(keyData: Data(xoredBytes))
+    }
+
     // MARK: 
     
     override public func isEqual(_ object: Any?) -> Bool {