[nrf toup][nrfconnect] Handle DAC key in ITS when KMU migration is selected

Detect when the DAC private key remains in PSA ITS while factory data
is configured to migrate the key to CRACEN KMU. Abort boot in that
case unless CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU_ITS_FALLBACK is enabled;
then sign attestations with the ITS key and log a warning because
ITS-to-KMU migration is not supported.

Extend KMU-related Kconfig dependencies to CRACEN_LIB_KMU.

Signed-off-by: Arkadiusz Balys <arkadiusz.balys@nordicsemi.no>

Author: ArekBalysNordic

config/nrfconnect/chip-module/Kconfig

@@ -319,6 +319,7 @@ endif # CHIP_FACTORY_DATA_NRFCONNECT_BACKEND
 
 # See config/zephyr/Kconfig for full definition
 config CHIP_FACTORY_RESET_ERASE_SETTINGS
+	depends on !CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU_ITS_FALLBACK
 	default y if !CHIP_CRYPTO_PSA_DAC_PRIV_KEY_ITS || BUILD_WITH_TFM
 
 config CHIP_CRYPTO_PSA_MIGRATE_DAC_PRIV_KEY
@@ -331,7 +332,7 @@ if CHIP_CRYPTO_PSA_MIGRATE_DAC_PRIV_KEY
 
 choice CHIP_CRYPTO_PSA_DAC_PRIV_KEY_MIGRATION_DEST
 	prompt "Destination for DAC private key migration"
-	default CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU if CRACEN_KMU
+	default CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU if (CRACEN_KMU || CRACEN_LIB_KMU)
 	default CHIP_CRYPTO_PSA_DAC_PRIV_KEY_ITS
 
 config CHIP_CRYPTO_PSA_DAC_PRIV_KEY_ITS
@@ -344,7 +345,7 @@ config CHIP_CRYPTO_PSA_DAC_PRIV_KEY_ITS
 
 config CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU
 	bool "Migrate DAC private key from factory data to CRACEN KMU"
-	depends on CRACEN_KMU
+	depends on (CRACEN_KMU || CRACEN_LIB_KMU)
 	help
 	  Move DAC private key from the factory data set to the CRACEN Key Management Unit (KMU) secure
 	  storage and remove it. After the first boot of the device the DAC private key will be
@@ -367,11 +368,22 @@ config CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU_ENCRYPTED
 	help
 	  Encrypt the DAC private key in the CRACEN KMU secure storage.
 
+config CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU_ITS_FALLBACK
+	bool "Use DAC private key from PSA ITS when KMU migration is configured"
+	depends on CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU
+	default y
+	help
+	  When CRACEN KMU is selected as the DAC private key migration destination but
+	  the key is still stored in PSA ITS (for example after switching the migration
+	  destination from ITS to KMU), allow the device to boot by signing with the
+	  ITS key and logging a warning instead of aborting. Automatic migration from
+	  ITS to KMU is not supported, re-provision the device to move the key to KMU.
+
 endif # CHIP_CRYPTO_PSA_MIGRATE_DAC_PRIV_KEY
 
 config CHIP_STORE_KEYS_IN_KMU
 	bool "Use KMU to store crypto keys"
-	depends on CRACEN_KMU
+	depends on (CRACEN_KMU || CRACEN_LIB_KMU)
 	select EXPERIMENTAL
 	help
 	  Stores cryptographic materials like keys in the KMU if available on the device.

src/platform/nrfconnect/FactoryDataProvider.cpp

@@ -85,6 +85,9 @@ CHIP_ERROR FactoryDataProvider<FlashFactoryData>::Init()
     }
 
 #ifdef CONFIG_CHIP_CRYPTO_PSA
+#ifdef CONFIG_CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU
+    FallbackToItsIfNeeded();
+#endif
     VerifyOrDie(MoveDACPrivateKeyToSecureStorage(factoryData, factoryDataSize) == CHIP_NO_ERROR);
 #endif
 
@@ -125,14 +128,25 @@ CHIP_ERROR FactoryDataProvider<FlashFactoryData>::MoveDACPrivateKeyToSecureStora
     memset(clearedDACPrivKey, 0x00, sizeof(clearedDACPrivKey));
 
 // If key should be migrated to KMU save the KMU key slot to keyId.
-#ifdef CONFIG_CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU
+#if defined(CONFIG_CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU) && !defined(CONFIG_CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU_ITS_FALLBACK)
     mDACPrivKeyId = static_cast<psa_key_id_t>(PSA_KEY_ID_FROM_CRACEN_KMU_SLOT(
 #ifdef CONFIG_CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU_ENCRYPTED
         CRACEN_KMU_KEY_USAGE_SCHEME_ENCRYPTED,
 #else
         CRACEN_KMU_KEY_USAGE_SCHEME_RAW,
 #endif // CONFIG_CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU_ENCRYPTED
         CONFIG_CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU_SLOT_ID));
+#elif defined(CONFIG_CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU) && defined(CONFIG_CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU_ITS_FALLBACK)
+    if (!mUseDacPrivKeyFromIts)
+    {
+        mDACPrivKeyId = static_cast<psa_key_id_t>(PSA_KEY_ID_FROM_CRACEN_KMU_SLOT(
+#ifdef CONFIG_CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU_ENCRYPTED
+            CRACEN_KMU_KEY_USAGE_SCHEME_ENCRYPTED,
+#else
+            CRACEN_KMU_KEY_USAGE_SCHEME_RAW,
+#endif // CONFIG_CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU_ENCRYPTED
+            CONFIG_CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU_SLOT_ID));
+    }
 #endif // CONFIG_CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU
 
     // Check if factory data contains DAC private key
@@ -220,6 +234,37 @@ CHIP_ERROR FactoryDataProvider<FlashFactoryData>::MoveDACPrivateKeyToSecureStora
 
     return CHIP_NO_ERROR;
 }
+
+#ifdef CONFIG_CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU
+template <class FlashFactoryData>
+void FactoryDataProvider<FlashFactoryData>::FallbackToItsIfNeeded()
+{
+    const psa_key_id_t itsDacKeyId = to_underlying(chip::Crypto::KeyIdBase::DACPrivKey);
+
+    psa_key_attributes_t attributes = PSA_KEY_ATTRIBUTES_INIT;
+    const psa_status_t status       = psa_get_key_attributes(itsDacKeyId, &attributes);
+
+    psa_reset_key_attributes(&attributes);
+
+    if (status == PSA_SUCCESS)
+    {
+#ifdef CONFIG_CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU_ITS_FALLBACK
+        ChipLogProgress(DeviceLayer,
+                        "Warning: DAC private key found in PSA ITS while CRACEN KMU storage is configured. "
+                        "Using the ITS key for attestation signing. Automatic migration from ITS to KMU is "
+                        "not supported; re-provision the device to move the key to KMU.");
+        mUseDacPrivKeyFromIts = true;
+        mDACPrivKeyId         = itsDacKeyId;
+#else
+        ChipLogError(DeviceLayer,
+                     "DAC private key found in PSA ITS while CRACEN KMU storage is configured. "
+                     "Automatic migration from ITS to KMU is not supported. "
+                     "Re-provision the device.");
+        VerifyOrDie(false);
+#endif // CONFIG_CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU_ITS_FALLBACK
+    }
+}
+#endif // CONFIG_CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU
 #endif // CONFIG_CHIP_CRYPTO_PSA
 
 template <class FlashFactoryData>
@@ -288,7 +333,15 @@ CHIP_ERROR FactoryDataProvider<FlashFactoryData>::SignWithDeviceAttestationKey(c
 #ifdef CONFIG_CHIP_CRYPTO_PSA
     size_t outputLen = 0;
 
-    psa_status_t err = psa_sign_message(mDACPrivKeyId, PSA_ALG_ECDSA(PSA_ALG_SHA_256), messageToSign.data(), messageToSign.size(),
+    psa_key_id_t dacPrivKeyId = mDACPrivKeyId;
+#if defined(CONFIG_CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU) && defined(CONFIG_CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU_ITS_FALLBACK)
+    if (mUseDacPrivKeyFromIts)
+    {
+        dacPrivKeyId = static_cast<psa_key_id_t>(to_underlying(chip::Crypto::KeyIdBase::DACPrivKey));
+    }
+#endif
+
+    psa_status_t err = psa_sign_message(dacPrivKeyId, PSA_ALG_ECDSA(PSA_ALG_SHA_256), messageToSign.data(), messageToSign.size(),
                                         signature.Bytes(), signature.Capacity(), &outputLen);
 
     VerifyOrReturnError(!err, CHIP_ERROR_INTERNAL);

src/platform/nrfconnect/FactoryDataProvider.h

@@ -153,6 +153,10 @@ class FactoryDataProvider : public FactoryDataProviderBase
     CHIP_ERROR MoveDACPrivateKeyToSecureStorage(uint8_t * factoryDataPartition, size_t factoryDataSize);
 #endif
 
+#ifdef CONFIG_CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU
+    void FallbackToItsIfNeeded();
+#endif // CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU
+
     // ===== Members functions that implement the DeviceAttestationCredentialsProvider
     CHIP_ERROR GetCertificationDeclaration(MutableByteSpan & outBuffer) override;
     CHIP_ERROR GetFirmwareInformation(MutableByteSpan & out_firmware_info_buffer) override;
@@ -200,6 +204,9 @@ class FactoryDataProvider : public FactoryDataProviderBase
     FlashFactoryData mFlashFactoryData;
 #ifdef CONFIG_CHIP_CRYPTO_PSA
     psa_key_id_t mDACPrivKeyId = to_underlying(chip::Crypto::KeyIdBase::DACPrivKey);
+#if defined(CONFIG_CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU) && defined(CONFIG_CHIP_CRYPTO_PSA_DAC_PRIV_KEY_KMU_ITS_FALLBACK)
+    bool mUseDacPrivKeyFromIts = false;
+#endif
 #endif
 };