[crypto] Extend the OperationalKeystore API to allow migration (project-chip#31279)

ArekBalysNordic · web-flow · commit 61724ee35e24 · 2024-02-08T07:25:31.000Z
- Extended the OperationalKeystore API by mechanism for migration of
operational keys stored in one Operational Keystore implementation
to another.

- Extended the OperationalKeystore API by exporting keypair for Fabric.

- Added Unit tests to PersistentStorageOpKeyStore and PSAOpKeystore regarding
the new OperationalKeystore for migration and exporting OpKeys.

Added first unit tests, created export method
diff --git a/src/crypto/OperationalKeystore.h b/src/crypto/OperationalKeystore.h
@@ -119,6 +119,46 @@ class OperationalKeystore
      */
     virtual CHIP_ERROR CommitOpKeypairForFabric(FabricIndex fabricIndex) = 0;
 
+    /**
+     * @brief Try to read out the permanently committed operational keypair and save it to the buffer.
+     *
+     * @param fabricIndex - FabricIndex from which the keypair will be exported
+     * @param outKeypair - a reference to P256SerializedKeypair object to store the exported key.
+     * @retval CHIP_ERROR on success.
+     * @retval CHIP_ERROR_UNSUPPORTED_CHIP_FEATURE if the key cannot be exported due to security restrictions.
+     * @retval CHIP_ERROR_NOT_IMPLEMENTED if the exporting is not implemented for the cryptography backend.
+     * @retval CHIP_ERROR_INVALID_FABRIC_INDEX if provided wrong value of `fabricIndex`.
+     * @retval CHIP_ERROR_PERSISTED_STORAGE_VALUE_NOT_FOUND if there is no keypair found for `fabricIndex`.
+     * @retval CHIP_ERROR_BUFFER_TOO_SMALL if `outKeyPair` buffer is too small to store the read out keypair.
+     * @retval other CHIP_ERROR value on internal storage or cryptography backend errors.
+     */
+    virtual CHIP_ERROR ExportOpKeypairForFabric(FabricIndex fabricIndex, Crypto::P256SerializedKeypair & outKeypair)
+    {
+        return CHIP_ERROR_NOT_IMPLEMENTED;
+    };
+
+    /**
+     * @brief Migrate the operational keypair from another Operational keystore (`operationalKeystore`) implementation to this one.
+     *
+     * This method assumes that the operational key for given `fabricIndex` exists in the `operationalKeystore` storage or it has
+     * been already migrated to the new Operational Storage. If a key for the given `fabricIndex` does not exist in any of those
+     * keystores, then the method retuns CHIP_ERROR_PERSISTED_STORAGE_VALUE_NOT_FOUND.
+     *
+     * @param fabricIndex - FabricIndex for which to migrate the operational key
+     * @param operationalKeystore - a reference to the operationalKeystore implementation that may contain saved operational key
+     * for Fabric
+     * @retval CHIP_ERROR on success
+     * @retval CHIP_ERROR_UNSUPPORTED_CHIP_FEATURE if the key cannot be exported due to security restrictions.
+     * @retval CHIP_ERROR_NOT_IMPLEMENTED if the exporting is not implemented for the cryptography backend.
+     * @retval CHIP_ERROR_INVALID_FABRIC_INDEX if there is no keypair found for `fabricIndex`.
+     * @retval CHIP_ERROR_PERSISTED_STORAGE_VALUE_NOT_FOUND if there is no keypair found for `fabricIndex`.
+     * @retval other CHIP_ERROR value on internal storage or crypto engine errors.
+     */
+    virtual CHIP_ERROR MigrateOpKeypairForFabric(FabricIndex fabricIndex, OperationalKeystore & operationalKeystore) const
+    {
+        return CHIP_ERROR_NOT_IMPLEMENTED;
+    };
+
     /**
      * @brief Permanently remove the keypair associated with a fabric
      *
diff --git a/src/crypto/PSAOperationalKeystore.cpp b/src/crypto/PSAOperationalKeystore.cpp
@@ -16,6 +16,7 @@
  */
 
 #include "PSAOperationalKeystore.h"
+#include "PersistentStorageOperationalKeystore.h"
 
 #include <lib/support/CHIPMem.h>
 
@@ -135,6 +136,35 @@ CHIP_ERROR PSAOperationalKeystore::NewOpKeypairForFabric(FabricIndex fabricIndex
     return CHIP_NO_ERROR;
 }
 
+CHIP_ERROR PSAOperationalKeystore::PersistentP256Keypair::Deserialize(P256SerializedKeypair & input)
+{
+    CHIP_ERROR error                = CHIP_NO_ERROR;
+    psa_status_t status             = PSA_SUCCESS;
+    psa_key_attributes_t attributes = PSA_KEY_ATTRIBUTES_INIT;
+    psa_key_id_t keyId              = 0;
+    VerifyOrReturnError(input.Length() == mPublicKey.Length() + kP256_PrivateKey_Length, CHIP_ERROR_INVALID_ARGUMENT);
+
+    Destroy();
+
+    // Type based on ECC with the elliptic curve SECP256r1 -> PSA_ECC_FAMILY_SECP_R1
+    psa_set_key_type(&attributes, PSA_KEY_TYPE_ECC_KEY_PAIR(PSA_ECC_FAMILY_SECP_R1));
+    psa_set_key_bits(&attributes, kP256_PrivateKey_Length * 8);
+    psa_set_key_algorithm(&attributes, PSA_ALG_ECDSA(PSA_ALG_SHA_256));
+    psa_set_key_usage_flags(&attributes, PSA_KEY_USAGE_SIGN_MESSAGE);
+    psa_set_key_lifetime(&attributes, PSA_KEY_LIFETIME_PERSISTENT);
+    psa_set_key_id(&attributes, GetKeyId());
+
+    status = psa_import_key(&attributes, input.ConstBytes() + mPublicKey.Length(), kP256_PrivateKey_Length, &keyId);
+    VerifyOrExit(status == PSA_SUCCESS, error = CHIP_ERROR_INTERNAL);
+
+    memcpy(mPublicKey.Bytes(), input.ConstBytes(), mPublicKey.Length());
+
+exit:
+    psa_reset_key_attributes(&attributes);
+
+    return error;
+}
+
 CHIP_ERROR PSAOperationalKeystore::ActivateOpKeypairForFabric(FabricIndex fabricIndex, const Crypto::P256PublicKey & nocPublicKey)
 {
     VerifyOrReturnError(IsValidFabricIndex(fabricIndex) && mPendingFabricIndex == fabricIndex, CHIP_ERROR_INVALID_FABRIC_INDEX);
@@ -154,6 +184,40 @@ CHIP_ERROR PSAOperationalKeystore::CommitOpKeypairForFabric(FabricIndex fabricIn
     return CHIP_NO_ERROR;
 }
 
+CHIP_ERROR PSAOperationalKeystore::ExportOpKeypairForFabric(FabricIndex fabricIndex, Crypto::P256SerializedKeypair & outKeypair)
+{
+    // Currently exporting the key is forbidden in PSAOperationalKeystore because the PSA_KEY_USAGE_EXPORT usage flag is not set, so
+    // there is no need to compile the code for the device, but there should be an implementation for test purposes to verify if
+    // the psa_export_key returns an error.
+#if CHIP_CONFIG_TEST
+    VerifyOrReturnError(IsValidFabricIndex(fabricIndex), CHIP_ERROR_INVALID_FABRIC_INDEX);
+    VerifyOrReturnError(HasOpKeypairForFabric(fabricIndex), CHIP_ERROR_PERSISTED_STORAGE_VALUE_NOT_FOUND);
+
+    size_t outSize = 0;
+    psa_status_t status =
+        psa_export_key(PersistentP256Keypair(fabricIndex).GetKeyId(), outKeypair.Bytes(), outKeypair.Capacity(), &outSize);
+
+    if (status == PSA_ERROR_BUFFER_TOO_SMALL)
+    {
+        return CHIP_ERROR_BUFFER_TOO_SMALL;
+    }
+    else if (status == PSA_ERROR_NOT_PERMITTED)
+    {
+        return CHIP_ERROR_UNSUPPORTED_CHIP_FEATURE;
+    }
+    else if (status != PSA_SUCCESS)
+    {
+        return CHIP_ERROR_INTERNAL;
+    }
+
+    outKeypair.SetLength(outSize);
+
+    return CHIP_NO_ERROR;
+#else
+    return CHIP_ERROR_NOT_IMPLEMENTED;
+#endif
+}
+
 CHIP_ERROR PSAOperationalKeystore::RemoveOpKeypairForFabric(FabricIndex fabricIndex)
 {
     VerifyOrReturnError(IsValidFabricIndex(fabricIndex), CHIP_ERROR_INVALID_FABRIC_INDEX);
@@ -209,5 +273,31 @@ void PSAOperationalKeystore::ReleasePendingKeypair()
     mIsPendingKeypairActive = false;
 }
 
+CHIP_ERROR PSAOperationalKeystore::MigrateOpKeypairForFabric(FabricIndex fabricIndex,
+                                                             OperationalKeystore & operationalKeystore) const
+{
+    VerifyOrReturnError(IsValidFabricIndex(fabricIndex), CHIP_ERROR_INVALID_FABRIC_INDEX);
+
+    P256SerializedKeypair serializedKeypair;
+
+    // Do not allow overwriting the existing key and just remove it from the previous Operational Keystore if needed.
+    if (!HasOpKeypairForFabric(fabricIndex))
+    {
+        ReturnErrorOnFailure(operationalKeystore.ExportOpKeypairForFabric(fabricIndex, serializedKeypair));
+
+        PersistentP256Keypair keypair(fabricIndex);
+        ReturnErrorOnFailure(keypair.Deserialize(serializedKeypair));
+
+        // Migrated key is not useful anymore, remove it from the previous keystore.
+        ReturnErrorOnFailure(operationalKeystore.RemoveOpKeypairForFabric(fabricIndex));
+    }
+    else if (operationalKeystore.HasOpKeypairForFabric(fabricIndex))
+    {
+        ReturnErrorOnFailure(operationalKeystore.RemoveOpKeypairForFabric(fabricIndex));
+    }
+
+    return CHIP_NO_ERROR;
+}
+
 } // namespace Crypto
 } // namespace chip
diff --git a/src/crypto/PSAOperationalKeystore.h b/src/crypto/PSAOperationalKeystore.h
@@ -19,6 +19,7 @@
 
 #include <crypto/CHIPCryptoPALPSA.h>
 #include <crypto/OperationalKeystore.h>
+#include <lib/core/CHIPPersistentStorageDelegate.h>
 
 namespace chip {
 namespace Crypto {
@@ -31,7 +32,9 @@ class PSAOperationalKeystore final : public OperationalKeystore
     CHIP_ERROR NewOpKeypairForFabric(FabricIndex fabricIndex, MutableByteSpan & outCertificateSigningRequest) override;
     CHIP_ERROR ActivateOpKeypairForFabric(FabricIndex fabricIndex, const Crypto::P256PublicKey & nocPublicKey) override;
     CHIP_ERROR CommitOpKeypairForFabric(FabricIndex fabricIndex) override;
+    CHIP_ERROR ExportOpKeypairForFabric(FabricIndex fabricIndex, Crypto::P256SerializedKeypair & outKeypair) override;
     CHIP_ERROR RemoveOpKeypairForFabric(FabricIndex fabricIndex) override;
+    CHIP_ERROR MigrateOpKeypairForFabric(FabricIndex fabricIndex, OperationalKeystore & operationalKeystore) const;
     void RevertPendingKeypair() override;
     CHIP_ERROR SignWithOpKeypair(FabricIndex fabricIndex, const ByteSpan & message,
                                  Crypto::P256ECDSASignature & outSignature) const override;
@@ -53,13 +56,15 @@ class PSAOperationalKeystore final : public OperationalKeystore
         bool Exists() const;
         CHIP_ERROR Generate();
         CHIP_ERROR Destroy();
+        CHIP_ERROR Deserialize(P256SerializedKeypair & input);
     };
 
     void ReleasePendingKeypair();
 
     PersistentP256Keypair * mPendingKeypair = nullptr;
     FabricIndex mPendingFabricIndex         = kUndefinedFabricIndex;
     bool mIsPendingKeypairActive            = false;
+    PersistentStorageDelegate * mStorage    = nullptr;
 };
 
 } // namespace Crypto
diff --git a/src/crypto/PersistentStorageOperationalKeystore.cpp b/src/crypto/PersistentStorageOperationalKeystore.cpp
@@ -86,6 +86,52 @@ CHIP_ERROR StoreOperationalKey(FabricIndex fabricIndex, PersistentStorageDelegat
     return CHIP_NO_ERROR;
 }
 
+CHIP_ERROR ExportStoredOpKey(FabricIndex fabricIndex, PersistentStorageDelegate * storage,
+                             Crypto::P256SerializedKeypair & serializedOpKey)
+{
+    VerifyOrReturnError(storage != nullptr, CHIP_ERROR_INVALID_ARGUMENT);
+    VerifyOrReturnError(IsValidFabricIndex(fabricIndex), CHIP_ERROR_INVALID_FABRIC_INDEX);
+
+    // Use a SensitiveDataBuffer to get RAII secret data clearing on scope exit.
+    Crypto::SensitiveDataBuffer<OpKeyTLVMaxSize()> buf;
+
+    // Load up the operational key structure from storage
+    uint16_t size = static_cast<uint16_t>(buf.Capacity());
+    ReturnErrorOnFailure(
+        storage->SyncGetKeyValue(DefaultStorageKeyAllocator::FabricOpKey(fabricIndex).KeyName(), buf.Bytes(), size));
+
+    buf.SetLength(static_cast<size_t>(size));
+
+    // Read-out the operational key TLV entry.
+    TLV::ContiguousBufferTLVReader reader;
+    reader.Init(buf.Bytes(), buf.Length());
+
+    ReturnErrorOnFailure(reader.Next(TLV::kTLVType_Structure, TLV::AnonymousTag()));
+    TLV::TLVType containerType;
+    ReturnErrorOnFailure(reader.EnterContainer(containerType));
+
+    ReturnErrorOnFailure(reader.Next(kOpKeyVersionTag));
+    uint16_t opKeyVersion;
+    ReturnErrorOnFailure(reader.Get(opKeyVersion));
+    VerifyOrReturnError(opKeyVersion == kOpKeyVersion, CHIP_ERROR_VERSION_MISMATCH);
+
+    ReturnErrorOnFailure(reader.Next(kOpKeyDataTag));
+    {
+        ByteSpan keyData;
+        ReturnErrorOnFailure(reader.GetByteView(keyData));
+
+        // Unfortunately, we have to copy the data into a P256SerializedKeypair.
+        VerifyOrReturnError(keyData.size() <= serializedOpKey.Capacity(), CHIP_ERROR_BUFFER_TOO_SMALL);
+
+        ReturnErrorOnFailure(reader.ExitContainer(containerType));
+
+        memcpy(serializedOpKey.Bytes(), keyData.data(), keyData.size());
+        serializedOpKey.SetLength(keyData.size());
+    }
+
+    return CHIP_NO_ERROR;
+}
+
 /** WARNING: This can leave the operational key on the stack somewhere, since many of the platform
  *           APIs use stack buffers and do not sanitize! This implementation is for example purposes
  *           only of the API and it is recommended to avoid directly accessing raw private key bits
@@ -106,56 +152,17 @@ CHIP_ERROR SignWithStoredOpKey(FabricIndex fabricIndex, PersistentStorageDelegat
     }
 
     // Scope 1: Load up the keypair data from storage
+    P256SerializedKeypair serializedOpKey;
+    CHIP_ERROR err = ExportStoredOpKey(fabricIndex, storage, serializedOpKey);
+    if (CHIP_ERROR_PERSISTED_STORAGE_VALUE_NOT_FOUND == err)
     {
-        // Use a SensitiveDataBuffer to get RAII secret data clearing on scope exit.
-        Crypto::SensitiveDataBuffer<OpKeyTLVMaxSize()> buf;
-
-        // Load up the operational key structure from storage
-        uint16_t size = static_cast<uint16_t>(buf.Capacity());
-        CHIP_ERROR err =
-            storage->SyncGetKeyValue(DefaultStorageKeyAllocator::FabricOpKey(fabricIndex).KeyName(), buf.Bytes(), size);
-        if (err == CHIP_ERROR_PERSISTED_STORAGE_VALUE_NOT_FOUND)
-        {
-            err = CHIP_ERROR_INVALID_FABRIC_INDEX;
-        }
-        ReturnErrorOnFailure(err);
-        buf.SetLength(static_cast<size_t>(size));
-
-        // Read-out the operational key TLV entry.
-        TLV::ContiguousBufferTLVReader reader;
-        reader.Init(buf.Bytes(), buf.Length());
-
-        ReturnErrorOnFailure(reader.Next(TLV::kTLVType_Structure, TLV::AnonymousTag()));
-        TLV::TLVType containerType;
-        ReturnErrorOnFailure(reader.EnterContainer(containerType));
-
-        ReturnErrorOnFailure(reader.Next(kOpKeyVersionTag));
-        uint16_t opKeyVersion;
-        ReturnErrorOnFailure(reader.Get(opKeyVersion));
-        VerifyOrReturnError(opKeyVersion == kOpKeyVersion, CHIP_ERROR_VERSION_MISMATCH);
-
-        ReturnErrorOnFailure(reader.Next(kOpKeyDataTag));
-        {
-            ByteSpan keyData;
-            Crypto::P256SerializedKeypair serializedOpKey;
-            ReturnErrorOnFailure(reader.GetByteView(keyData));
-
-            // Unfortunately, we have to copy the data into a P256SerializedKeypair.
-            VerifyOrReturnError(keyData.size() <= serializedOpKey.Capacity(), CHIP_ERROR_BUFFER_TOO_SMALL);
-
-            // Before doing anything with the key, validate format further.
-            ReturnErrorOnFailure(reader.ExitContainer(containerType));
-            ReturnErrorOnFailure(reader.VerifyEndOfContainer());
-
-            memcpy(serializedOpKey.Bytes(), keyData.data(), keyData.size());
-            serializedOpKey.SetLength(keyData.size());
-
-            // Load-up key material
-            // WARNING: This makes use of the raw key bits
-            ReturnErrorOnFailure(transientOperationalKeypair->Deserialize(serializedOpKey));
-        }
+        return CHIP_ERROR_INVALID_FABRIC_INDEX;
     }
 
+    // Load-up key material
+    // WARNING: This makes use of the raw key bits
+    ReturnErrorOnFailure(transientOperationalKeypair->Deserialize(serializedOpKey));
+
     // Scope 2: Sign message with the keypair
     return transientOperationalKeypair->ECDSA_sign_msg(message.data(), message.size(), outSignature);
 }
@@ -251,6 +258,13 @@ CHIP_ERROR PersistentStorageOperationalKeystore::CommitOpKeypairForFabric(Fabric
     return CHIP_NO_ERROR;
 }
 
+CHIP_ERROR PersistentStorageOperationalKeystore::ExportOpKeypairForFabric(FabricIndex fabricIndex,
+                                                                          Crypto::P256SerializedKeypair & outKeypair)
+{
+    VerifyOrReturnError(mStorage != nullptr, CHIP_ERROR_INCORRECT_STATE);
+    return ExportStoredOpKey(fabricIndex, mStorage, outKeypair);
+}
+
 CHIP_ERROR PersistentStorageOperationalKeystore::RemoveOpKeypairForFabric(FabricIndex fabricIndex)
 {
     VerifyOrReturnError(mStorage != nullptr, CHIP_ERROR_INCORRECT_STATE);
@@ -310,4 +324,36 @@ void PersistentStorageOperationalKeystore::ReleaseEphemeralKeypair(Crypto::P256K
     Platform::Delete<Crypto::P256Keypair>(keypair);
 }
 
+CHIP_ERROR PersistentStorageOperationalKeystore::MigrateOpKeypairForFabric(FabricIndex fabricIndex,
+                                                                           OperationalKeystore & operationalKeystore) const
+{
+    VerifyOrReturnError(mStorage != nullptr, CHIP_ERROR_INCORRECT_STATE);
+    VerifyOrReturnError(IsValidFabricIndex(fabricIndex), CHIP_ERROR_INVALID_FABRIC_INDEX);
+
+    P256SerializedKeypair serializedKeypair;
+
+    // Do not allow overwriting the existing key and just remove it from the previous Operational Keystore if needed.
+    if (!HasOpKeypairForFabric(fabricIndex))
+    {
+        ReturnErrorOnFailure(operationalKeystore.ExportOpKeypairForFabric(fabricIndex, serializedKeypair));
+
+        auto operationalKeypair = Platform::MakeUnique<P256Keypair>();
+        if (!operationalKeypair)
+        {
+            return CHIP_ERROR_NO_MEMORY;
+        }
+
+        ReturnErrorOnFailure(operationalKeypair->Deserialize(serializedKeypair));
+        ReturnErrorOnFailure(StoreOperationalKey(fabricIndex, mStorage, operationalKeypair.get()));
+
+        ReturnErrorOnFailure(operationalKeystore.RemoveOpKeypairForFabric(fabricIndex));
+    }
+    else if (operationalKeystore.HasOpKeypairForFabric(fabricIndex))
+    {
+        ReturnErrorOnFailure(operationalKeystore.RemoveOpKeypairForFabric(fabricIndex));
+    }
+
+    return CHIP_NO_ERROR;
+}
+
 } // namespace chip
diff --git a/src/crypto/PersistentStorageOperationalKeystore.h b/src/crypto/PersistentStorageOperationalKeystore.h
@@ -81,12 +81,14 @@ class PersistentStorageOperationalKeystore : public Crypto::OperationalKeystore
     CHIP_ERROR NewOpKeypairForFabric(FabricIndex fabricIndex, MutableByteSpan & outCertificateSigningRequest) override;
     CHIP_ERROR ActivateOpKeypairForFabric(FabricIndex fabricIndex, const Crypto::P256PublicKey & nocPublicKey) override;
     CHIP_ERROR CommitOpKeypairForFabric(FabricIndex fabricIndex) override;
+    CHIP_ERROR ExportOpKeypairForFabric(FabricIndex fabricIndex, Crypto::P256SerializedKeypair & outKeypair) override;
     CHIP_ERROR RemoveOpKeypairForFabric(FabricIndex fabricIndex) override;
     void RevertPendingKeypair() override;
     CHIP_ERROR SignWithOpKeypair(FabricIndex fabricIndex, const ByteSpan & message,
                                  Crypto::P256ECDSASignature & outSignature) const override;
     Crypto::P256Keypair * AllocateEphemeralKeypairForCASE() override;
     void ReleaseEphemeralKeypair(Crypto::P256Keypair * keypair) override;
+    CHIP_ERROR MigrateOpKeypairForFabric(FabricIndex fabricIndex, OperationalKeystore & operationalKeystore) const override;
 
 protected:
     void ResetPendingKey()
diff --git a/src/crypto/tests/TestPSAOpKeyStore.cpp b/src/crypto/tests/TestPSAOpKeyStore.cpp
diff --git a/src/crypto/tests/TestPersistentStorageOpKeyStore.cpp b/src/crypto/tests/TestPersistentStorageOpKeyStore.cpp
