service: nfp: Allow amiibos without keys

src/core/hle/service/nfp/amiibo_crypto.cpp

@@ -9,6 +9,7 @@
 #include <mbedtls/hmac_drbg.h>
 
 #include "common/fs/file.h"
+#include "common/fs/fs.h"
 #include "common/fs/path_util.h"
 #include "common/logging/log.h"
 #include "core/hle/service/mii/mii_manager.h"
@@ -279,7 +280,7 @@ bool LoadKeys(InternalKey& locked_secret, InternalKey& unfixed_info) {
                                        Common::FS::FileType::BinaryFile};
 
     if (!keys_file.IsOpen()) {
-        LOG_ERROR(Service_NFP, "No keys detected");
+        LOG_ERROR(Service_NFP, "Failed to open key file");
         return false;
     }
 
@@ -295,6 +296,11 @@ bool LoadKeys(InternalKey& locked_secret, InternalKey& unfixed_info) {
     return true;
 }
 
+bool IsKeyAvailable() {
+    const auto yuzu_keys_dir = Common::FS::GetYuzuPath(Common::FS::YuzuPath::KeysDir);
+    return Common::FS::Exists(yuzu_keys_dir / "key_retail.bin");
+}
+
 bool DecodeAmiibo(const EncryptedNTAG215File& encrypted_tag_data, NTAG215File& tag_data) {
     InternalKey locked_secret{};
     InternalKey unfixed_info{};

src/core/hle/service/nfp/amiibo_crypto.h

@@ -91,6 +91,9 @@ void Cipher(const DerivedKeys& keys, const NTAG215File& in_data, NTAG215File& ou
 /// Loads both amiibo keys from key_retail.bin
 bool LoadKeys(InternalKey& locked_secret, InternalKey& unfixed_info);
 
+/// Returns true if key_retail.bin exist
+bool IsKeyAvailable();
+
 /// Decodes encripted amiibo data returns true if output is valid
 bool DecodeAmiibo(const EncryptedNTAG215File& encrypted_tag_data, NTAG215File& tag_data);
 

src/core/hle/service/nfp/nfp_device.cpp

@@ -234,6 +234,14 @@ Result NfpDevice::Mount(MountTarget mount_target_) {
         return NotAnAmiibo;
     }
 
+    // Mark amiibos as read only when keys are missing
+    if (!AmiiboCrypto::IsKeyAvailable()) {
+        LOG_ERROR(Service_NFP, "No keys detected");
+        device_state = DeviceState::TagMounted;
+        mount_target = MountTarget::Rom;
+        return ResultSuccess;
+    }
+
     if (!AmiiboCrypto::DecodeAmiibo(encrypted_tag_data, tag_data)) {
         LOG_ERROR(Service_NFP, "Can't decode amiibo {}", device_state);
         return CorruptedData;