Ensure legacy closed groups still work

SessionMessagingKit/Sending & Receiving/MessageReceiver.swift

@@ -71,6 +71,7 @@ public enum MessageReceiver {
                 (plaintext, sender) = try decryptWithSessionProtocol(ciphertext: ciphertext, using: userX25519KeyPair)
             case .closedGroupCiphertext:
                 guard let hexEncodedGroupPublicKey = envelope.source, SNMessagingKitConfiguration.shared.storage.isClosedGroup(hexEncodedGroupPublicKey) else { throw Error.invalidGroupPublicKey }
+                do {
                     var keyPairs = Storage.shared.getClosedGroupEncryptionKeyPairs(for: hexEncodedGroupPublicKey)
                     guard !keyPairs.isEmpty else { throw Error.noGroupKeyPair }
                     // Loop through all known group key pairs in reverse order (i.e. try the latest key pair first (which'll more than
@@ -89,6 +90,12 @@ public enum MessageReceiver {
                         }
                     }
                     try decrypt()
+                } catch {
+                    // Fall back on the V1 method
+                    guard let privateKey = SNMessagingKitConfiguration.shared.storage.getClosedGroupPrivateKey(for: hexEncodedGroupPublicKey) else { throw Error.noGroupKeyPair }
+                    let keyPair = try ECKeyPair(publicKeyData: Data(hex: hexEncodedGroupPublicKey.removing05PrefixIfNeeded()), privateKeyData: Data(hex: privateKey))
+                    (plaintext, sender) = try decryptWithSessionProtocol(ciphertext: ciphertext, using: keyPair)
+                }
                 groupPublicKey = envelope.source
             default: throw Error.unknownEnvelopeType
             }

SignalUtilitiesKit/Configuration.swift

@@ -10,6 +10,7 @@ public final class Configuration : NSObject {
     @objc public static func performMainSetup() {
         SNMessagingKit.configure(storage: Storage.shared)
         SNSnodeKit.configure(storage: Storage.shared)
+        SNProtocolKit.configure(storage: Storage.shared, sharedSenderKeysDelegate: MessageSender.shared)
         SNUtilitiesKit.configure(owsPrimaryStorage: OWSPrimaryStorage.shared(), maxFileSize: UInt(Double(FileServerAPI.maxFileSize) / FileServerAPI.fileSizeORMultiplier))
     }
 }