sys/psa_crypto: implement persistent key storage

sys/psa_crypto/Kconfig

@@ -20,5 +20,6 @@ rsource "Kconfig.keys"
 
 rsource "psa_se_mgmt/Kconfig"
 rsource "psa_key_slot_mgmt/Kconfig"
+rsource "psa_persistent_storage/Kconfig"
 
 endif # MODULE_PSA_CRYPTO

sys/psa_crypto/Makefile

@@ -8,6 +8,10 @@ ifneq (,$(filter psa_key_slot_mgmt,$(USEMODULE)))
   DIRS += psa_key_slot_mgmt
 endif
 
+ifneq (,$(filter psa_persistent_storage,$(USEMODULE)))
+  DIRS += psa_persistent_storage
+endif
+
 ifneq (,$(filter psa_se_mgmt,$(USEMODULE)))
   DIRS += psa_se_mgmt
 endif

sys/psa_crypto/Makefile.dep

@@ -3,6 +3,15 @@ ifneq (,$(filter psa_crypto,$(USEMODULE)))
   USEMODULE += prng_musl_lcg
 endif
 
+ifneq (,$(filter psa_persistent_storage, $(USEMODULE)))
+  USEPKG += nanocbor
+  USEPKG += littlefs2
+  USEMODULE += vfs
+  USEMODULE += vfs_default
+  USEMODULE += vfs_auto_format
+  USEMODULE += vfs_auto_mount
+endif
+
 # Asymmetric
 ifneq (,$(filter psa_asymmetric,$(USEMODULE)))
   USEMODULE += psa_key_slot_mgmt

sys/psa_crypto/doc.txt

@@ -112,8 +112,10 @@
  * Persistent keys will also be written into flash memory for later access. To destroy
  * them they must be explicitly deleted with the `psa_destroy_key()` function.
  *
- * @note    So far this implementation only supports volatile storage. Persistent storage
- *          will be added in the future.
+ * @note    Persistent key storage can be optionally enabled on `native` and on the `nRF52840dk`.
+ *          For this, add `USEMODULE += psa_persistent_storage` to your application makefile
+ *          or `CONFIG_MODULE_PSA_PERSISTENT_STORAGE=y` to your `app.config.test` file.
+ *          Example: `tests/sys/psa_crypto_persistent_storage`
  *
  * #### Lifetime Encoding
  * When creating a key, the user needs to specify a lifetime value, which actually consists
@@ -233,6 +235,9 @@
  * When using `app.config.test` files in your application directory, you need to write the
  * names in uppercase and add the prefix `CONFIG_MODULE_` to all of them.
  *
+ * ### Key Storage
+ * - Persistent Key Storage: psa_persistent_storage
+ *
  * ### Asymmetric Crypto
  * - Base: psa_asymmetric
  *

sys/psa_crypto/include/psa_crypto_cbor_encoder.h

@@ -0,0 +1,124 @@
+/*
+ * Copyright (C) 2023 HAW Hamburg
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     sys_psa_crypto
+ * @defgroup    sys_psa_crypto_cbor_encoder     Module for encoding PSA keys in CBOR
+ * @{
+ *
+ * @file        psa_crypto_cbor_encoder.h
+ * @brief
+ *
+ * @author      Lena Boeckmann <lena.boeckmann@haw-hamburg.de>
+ *
+ */
+
+#ifndef PSA_CRYPTO_CBOR_ENCODER_H
+#define PSA_CRYPTO_CBOR_ENCODER_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include "psa_crypto_slot_management.h"
+
+/**
+ * @brief   Encodes a basic key slot in CBOR
+ *
+ *          Single Key Format:
+ *          - Key Slot Array:
+ *              - Attributes Array[5]:
+ *                  - ID (First bytes are always ID for quick lookup)
+ *                  - Type
+ *                  - Bits
+ *                  - Lifetime
+ *                  - Policy Array[2]:
+ *                      - Usage
+ *                      - Algorithm
+ *              - Key Array[2]
+ *                  - Key Length
+ *                  - Key Data Array[slot->key.data_len]
+ *                      - Key Data
+ *
+ *          Asymmetric Key Pair Format:
+ *          - Key Slot Array:
+ *              - Attributes Array[5]:
+ *                  - ID (First bytes are always ID for quick lookup)
+ *                  - Type
+ *                  - Bits
+ *                  - Lifetime
+ *                  - Policy Array[2]:
+ *                      - Usage
+ *                      - Algorithm
+ *              - Key Pair Array[2]:
+ *                  - Private Key Array[2]
+ *                      - Private Key Data Length
+ *                      - Private Key Data Array[slot->key.data_len]
+ *                          - Private Key Data
+ *                  - Public Key Array[2]
+ *                      - Public Key Length
+ *                      - Public Key Array[pubkey_data_len]
+ *                          - Public Key Data
+ *
+ *          Protected Key Format:
+ *          - Key Slot Array:
+ *              - ID (First bytes are always ID for quick lookup)
+ *              - Type
+ *              - Bits
+ *              - Lifetime
+ *              - Policy Array[2]:
+ *                      - Usage
+ *                      - Algorithm
+ *              - Prot Key Array[1-2]
+ *                  - Key Slot Number
+ *                  *optional:*
+ *                  - Public Key Array[2]
+ *                      - Public Key Len
+ *                      - Public Key Array[pubkey_data_len]
+ *                          - Public Key Data
+ *
+ * @param slot          Pointer to slot containing the key to encode
+ * @param output        Buffer to write the encoded key to
+ * @param output_len    Length of output buffer
+ * @param output_size   Pointer to write actual length of encoding
+ *
+ * @return psa_status_t
+ */
+psa_status_t psa_encode_key_slot(psa_key_slot_t *slot, uint8_t *output,
+                                     size_t output_len, size_t *output_size);
+
+/**
+ * @brief   Decode CBOR encoded key data and write to PSA key slot. Only decodes the key and should
+ *          be called in combination with psa_decode_key_attributes.
+ *
+ * @param slot          Pointer to key slot to write decoded key to
+ * @param cbor_buf      Buffer containing CBOR encoded data
+ * @param cbor_buf_size Size of @p cbor_buf
+ * @return psa_status_t
+ */
+psa_status_t psa_decode_key_slot_data(psa_key_slot_t *slot, uint8_t *cbor_buf,
+                                      size_t cbor_buf_size);
+
+/**
+ * @brief   Decode CBOR PSA key attributes. Only decodes key attributes and not the actual key.
+ *          Key can be decoded with psa_decode_key_slot_data.
+ *
+ * @param   attr            Key attribute struct to store decoded attributes
+ * @param   cbor_buf        Buffer containing CBOR encoded data
+ * @param   cbor_buf_size    Size of @p cbor_buf
+ * @return  psa_status_t
+ */
+psa_status_t psa_decode_key_attributes(psa_key_attributes_t *attr, uint8_t *cbor_buf,
+                                       size_t cbor_buf_size);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* PSA_CRYPTO_CBOR_ENCODER_H */
+/** @} */

sys/psa_crypto/include/psa_crypto_persistent_storage.h

@@ -0,0 +1,69 @@
+/*
+ * Copyright (C) 2023 HAW Hamburg
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup         sys_psa_crypto
+ * @defgroup        sys_psa_crypto_pers_stor PSA Crypto Persistent Storage API
+ * @{
+ *
+ * @file        psa_crypto_persistent_storage.h
+ * @brief
+ *
+ * @author      Lena Boeckmann <lena.boeckmann@haw-hamburg.de>
+ *
+ */
+
+#ifndef PSA_CRYPTO_PERSISTENT_STORAGE_H
+#define PSA_CRYPTO_PERSISTENT_STORAGE_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include "psa/crypto.h"
+
+/**
+ * @brief   Writes a CBOR encoded key slot to a file
+ *
+ * @param   id              ID of slot, used as filename
+ * @param   cbor_buf        Pointer to CBOR encoded data
+ * @param   cbor_buf_len    Length of CBOR encoded data
+ * @return  psa_status_t
+ */
+psa_status_t psa_write_cbor_encoded_key_slot_to_file(psa_key_id_t id,
+                                                     uint8_t* cbor_buf,
+                                                     size_t cbor_buf_len);
+
+/**
+ * @brief   Reads a CBOR encoded key slot from a file
+ *
+ * @param   id              ID of the desired key
+ * @param   cbor_buf        Output buffer to write CBOR data to
+ * @param   cbor_buf_size   Size of output buffer
+ * @param   cbor_data_len   Actual length of CBOR encoded data
+ * @return  psa_status_t
+ */
+psa_status_t psa_get_cbor_encoded_key_slot_from_file(psa_key_id_t id,
+                                                     uint8_t *cbor_buf,
+                                                     size_t cbor_buf_size,
+                                                     size_t *cbor_data_len);
+
+/**
+ * @brief   Destroy a key in persistent storage
+ *
+ * @param   key_id  ID of the key to be destroyed
+ * @return  psa_status_t
+ */
+psa_status_t psa_destroy_persistent_key(psa_key_id_t key_id);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* PSA_CRYPTO_PERSISTENT_STORAGE_H */
+/** @} */

sys/psa_crypto/include/psa_crypto_slot_management.h

@@ -84,6 +84,51 @@ typedef struct {
     } key;                                      /**< Key data structure */
 } psa_key_slot_t;
 
+#if IS_USED(MODULE_PSA_SECURE_ELEMENT) || IS_USED(MODULE_EMBUNIT)
+/**
+ * @brief   Structure for a protected key slot.
+ *
+ *          These slots hold Slot Numbers for keys in protected storage and, if the key type is an
+ *          asymmetric key pair, the public key.
+ */
+typedef struct {
+    clist_node_t node;
+    size_t lock_count;
+    psa_key_attributes_t attr;
+    struct prot_key_data {
+        psa_key_slot_number_t slot_number;
+#if IS_USED(MODULE_PSA_SECURE_ELEMENT_ASYMMETRIC) || IS_USED(MODULE_EMBUNIT)
+        uint8_t pubkey_data[PSA_EXPORT_PUBLIC_KEY_MAX_SIZE];
+        size_t pubkey_data_len;
+#endif
+    } key;
+} psa_prot_key_slot_t;
+#endif /* MODULE_PSA_SECURE_ELEMENT_ASYMMETRIC */
+
+#if IS_USED(MODULE_PSA_ASYMMETRIC)
+/**
+ * @brief   Structure for asymmetric key pairs.
+ *
+ *          Contains asymmetric private and public key pairs.
+ *
+ */
+typedef struct {
+    clist_node_t node;
+    size_t lock_count;
+    psa_key_attributes_t attr;
+    struct key_pair_data {
+        /**  Contains asymmetric private key*/
+        uint8_t privkey_data[PSA_BITS_TO_BYTES(PSA_MAX_PRIV_KEY_SIZE)];
+        /** Contains actual size of asymmetric private key */
+        size_t privkey_data_len;
+        /** Contains asymmetric public key */
+        uint8_t pubkey_data[PSA_EXPORT_PUBLIC_KEY_MAX_SIZE];
+        /*!< Contains actual size of asymmetric private key */
+        size_t pubkey_data_len;
+    } key;
+} psa_key_pair_slot_t;
+#endif /* MODULE_PSA_ASYMMETRIC */
+
 /**
  * @brief   Initializes the allocated key slots and prepares the internal key slot lists.
  */
@@ -163,6 +208,14 @@ void psa_wipe_all_key_slots(void);
  */
 psa_status_t psa_get_and_lock_key_slot(psa_key_id_t id, psa_key_slot_t **slot);
 
+/**
+ * @brief   Store a key slot in persistent storage
+ *
+ * @param   slot    Pointer to slot to store in persistent storage
+ * @return  psa_status_t
+ */
+psa_status_t psa_persist_key_slot_in_storage(psa_key_slot_t *slot);
+
 /**
  * @brief   Find a currently empty key slot that is appropriate for the key.
  *