Fixed a legacy group message decryption issue

Fixed a bug where we were incorrectly generating and requiring 64 byte secrets for legacy groups (we only need 32 bytes), since we do length checks before calling the libSession C API (to prevent crashes) we would fail before attempting to decrypt because the key was too short

LibSession-Util

@@ -1 +1 @@
-Subproject commit af0ab996da46bcbeeea5e70831cda7e23c955243
+Subproject commit 2bf8c81443494f227a9509ddd95889f196b668d6

Session.xcodeproj/project.pbxproj

@@ -7673,7 +7673,7 @@
 				CLANG_WARN__ARC_BRIDGE_CAST_NONARC = YES;
 				CLANG_WARN__DUPLICATE_METHOD_MATCH = YES;
 				CODE_SIGN_IDENTITY = "iPhone Developer";
-				CURRENT_PROJECT_VERSION = 476;
+				CURRENT_PROJECT_VERSION = 478;
 				ENABLE_BITCODE = NO;
 				ENABLE_STRICT_OBJC_MSGSEND = YES;
 				ENABLE_TESTABILITY = YES;
@@ -7751,7 +7751,7 @@
 				CLANG_WARN__ARC_BRIDGE_CAST_NONARC = YES;
 				CLANG_WARN__DUPLICATE_METHOD_MATCH = YES;
 				CODE_SIGN_IDENTITY = "iPhone Distribution";
-				CURRENT_PROJECT_VERSION = 476;
+				CURRENT_PROJECT_VERSION = 478;
 				ENABLE_BITCODE = NO;
 				ENABLE_STRICT_OBJC_MSGSEND = YES;
 				GCC_NO_COMMON_BLOCKS = YES;

SessionMessagingKit/Crypto/Crypto+SessionMessagingKit.swift

@@ -168,9 +168,13 @@ public extension Crypto.Generator {
             var maybePlaintext: UnsafeMutablePointer<UInt8>? = nil
             var plaintextLen: Int = 0
 
+            // Note: We should only need a 32 byte key but there was a bug in 2.7.1 where we
+            // started generating 64 byte keys so, in order to support those, we accept allow
+            // both and the C code just takes the first 32 bytes (which is all that is needed
+            // from the 64 byte key anyway)
             guard
                 cX25519Pubkey.count == 32,
-                cX25519Seckey.count == 64,
+                (cX25519Seckey.count == 32 || cX25519Seckey.count == 64),
                 session_decrypt_incoming_legacy_group(
                     &cCiphertext,
                     cCiphertext.count,

SessionUtilitiesKit/Crypto/Crypto+SessionUtilitiesKit.swift

@@ -55,7 +55,7 @@ public extension Crypto.Generator {
     static func x25519KeyPair() -> Crypto.Generator<KeyPair> {
         return Crypto.Generator<KeyPair>(id: "x25519KeyPair") { () -> KeyPair in
             var pubkey: [UInt8] = [UInt8](repeating: 0, count: 32)
-            var seckey: [UInt8] = [UInt8](repeating: 0, count: 64)
+            var seckey: [UInt8] = [UInt8](repeating: 0, count: 32)
             
             guard session_curve25519_key_pair(&pubkey, &seckey) else { throw CryptoError.keyGenerationFailed }