securechip: make securechip_slot_t an internal type

A step towards making the securechip interface generic so other chips
can be used instead of ATECC608.

Author: NickeZ

src/keystore.c

@@ -72,7 +72,7 @@ USE_RESULT static keystore_error_t _stretch_retained_seed_encryption_key(
     if (!salt_hash_data(encryption_key, 32, purpose_in, salted_hashed)) {
         return KEYSTORE_ERR_SALT;
     }
-    if (securechip_kdf(SECURECHIP_SLOT_KDF, salted_hashed, 32, out)) {
+    if (securechip_kdf(salted_hashed, 32, out)) {
         return KEYSTORE_ERR_SECURECHIP;
     }
     if (!salt_hash_data(encryption_key, 32, purpose_out, salted_hashed)) {
@@ -187,9 +187,8 @@ static keystore_error_t _stretch_password(
     UTIL_CLEANUP_32(kdf_in);
     memcpy(kdf_in, password_salted_hashed, 32);
 
-    // First KDF on SECURECHIP_SLOT_ROLLKEY increments the monotonic
-    // counter. Call only once!
-    int securechip_result = securechip_kdf(SECURECHIP_SLOT_ROLLKEY, kdf_in, 32, kdf_out);
+    // First KDF on rollkey increments the monotonic counter. Call only once!
+    int securechip_result = securechip_kdf_rollkey(kdf_in, 32, kdf_out);
     if (securechip_result) {
         if (securechip_result_out != NULL) {
             *securechip_result_out = securechip_result;
@@ -199,7 +198,7 @@ static keystore_error_t _stretch_password(
     // Second KDF does not use the counter and we call it multiple times.
     for (int i = 0; i < KDF_NUM_ITERATIONS; i++) {
         memcpy(kdf_in, kdf_out, 32);
-        securechip_result = securechip_kdf(SECURECHIP_SLOT_KDF, kdf_in, 32, kdf_out);
+        securechip_result = securechip_kdf(kdf_in, 32, kdf_out);
         if (securechip_result) {
             if (securechip_result_out != NULL) {
                 *securechip_result_out = securechip_result;

src/securechip/securechip.c

@@ -26,6 +26,18 @@
 #include <host/atca_host.h>
 #pragma GCC diagnostic pop
 
+typedef enum {
+    SECURECHIP_SLOT_IO_PROTECTION_KEY = 0,
+    SECURECHIP_SLOT_AUTHKEY = 1,
+    SECURECHIP_SLOT_ENCRYPTION_KEY = 2,
+    SECURECHIP_SLOT_ROLLKEY = 3,
+    SECURECHIP_SLOT_KDF = 4,
+    SECURECHIP_SLOT_ATTESTATION = 5,
+    SECURECHIP_SLOT_ECC_UNSAFE_SIGN = 6,
+    SECURECHIP_SLOT_DATA0 = 9,
+    // The other slots are currently not in use.
+} securechip_slot_t;
+
 // Chip Configuration, generated with "make generate-atecc608-config"
 // The first 16 bytes, as well as the LockValue/LockConfig can't be changed and are ignored when
 // writing the configuration to the device. Locking is performed via the Lock command during setup,
@@ -515,7 +527,7 @@ bool securechip_update_keys(void)
     return _update_kdf_key() == ATCA_SUCCESS;
 }
 
-int securechip_kdf(securechip_slot_t slot, const uint8_t* msg, size_t len, uint8_t* kdf_out)
+static int _securechip_kdf(securechip_slot_t slot, const uint8_t* msg, size_t len, uint8_t* kdf_out)
 {
     if (len > 127 || (slot != SECURECHIP_SLOT_ROLLKEY && slot != SECURECHIP_SLOT_KDF)) {
         return SC_ERR_INVALID_ARGS;
@@ -572,6 +584,16 @@ int securechip_kdf(securechip_slot_t slot, const uint8_t* msg, size_t len, uint8
     return atcah_io_decrypt(&io_dec_params);
 }
 
+int securechip_kdf(const uint8_t* msg, size_t len, uint8_t* kdf_out)
+{
+    return _securechip_kdf(SECURECHIP_SLOT_KDF, msg, len, kdf_out);
+}
+
+int securechip_kdf_rollkey(const uint8_t* msg, size_t len, uint8_t* kdf_out)
+{
+    return _securechip_kdf(SECURECHIP_SLOT_ROLLKEY, msg, len, kdf_out);
+}
+
 bool securechip_gen_attestation_key(uint8_t* pubkey_out)
 {
     ATCA_STATUS result = _authorize_key();

src/securechip/securechip.h

@@ -49,18 +49,6 @@ typedef struct {
     void (*const random_32_bytes)(uint8_t* buf);
 } securechip_interface_functions_t;
 
-typedef enum {
-    SECURECHIP_SLOT_IO_PROTECTION_KEY = 0,
-    SECURECHIP_SLOT_AUTHKEY = 1,
-    SECURECHIP_SLOT_ENCRYPTION_KEY = 2,
-    SECURECHIP_SLOT_ROLLKEY = 3,
-    SECURECHIP_SLOT_KDF = 4,
-    SECURECHIP_SLOT_ATTESTATION = 5,
-    SECURECHIP_SLOT_ECC_UNSAFE_SIGN = 6,
-    SECURECHIP_SLOT_DATA0 = 9,
-    // The other slots are currently not in use.
-} securechip_slot_t;
-
 /**
  * Initializes the cryptoauthlib communication, by providing a custom i2c chip
  * communication interface/bridge to cryptoauthlib. On first call, the chip
@@ -80,22 +68,26 @@ USE_RESULT int securechip_setup(const securechip_interface_functions_t* ifs);
 USE_RESULT bool securechip_update_keys(void);
 
 /**
- * Perform KDF using the key in predefined slot with the input msg.
- * Calling this function for SECURECHIP_SLOT_ROLLKEY also increments the
+ * Perform HMAC using the key in KDF slot with the input msg.
+ * @param[in] msg Use this msg as input
+ * @param[in] len Must be <= 127.
+ * @param[out] kdf_out Must have size 32. Result of the kdf will be stored here.
+ * Cannot be the same as `msg`.
+ * @return values of `securechip_error_t` if negative, values of `ATCA_STATUS` if positive, 0 on
+ */
+USE_RESULT int securechip_kdf(const uint8_t* msg, size_t len, uint8_t* kdf_out);
+
+/**
+ * Perform KDF using the key in rollkey slot with the input msg.
+ * Calling this function increments the
  * monotonic counter Counter0.
- * @param[in] slot should be one of SECURECHIP_SLOT_ROLLKEY and
- *            SECURECHIP_SLOT_KDF.
  * @param[in] msg Use this msg as input
  * @param[in] len Must be <= 127.
  * @param[out] kdf_out Must have size 32. Result of the kdf will be stored here.
  * Cannot be the same as `msg`.
  * @return values of `securechip_error_t` if negative, values of `ATCA_STATUS` if positive, 0 on
  */
-USE_RESULT int securechip_kdf(
-    securechip_slot_t slot,
-    const uint8_t* msg,
-    size_t len,
-    uint8_t* kdf_out);
+USE_RESULT int securechip_kdf_rollkey(const uint8_t* msg, size_t len, uint8_t* kdf_out);
 
 /**
  * Generates a new attestation device key and outputs the public key.

test/simulator/framework/mock_securechip.c

@@ -22,6 +22,11 @@
 #include <string.h>
 #include <wally_crypto.h>
 
+typedef enum {
+    SECURECHIP_SLOT_ROLLKEY = 3,
+    SECURECHIP_SLOT_KDF = 4,
+} securechip_slot_t;
+
 static uint32_t _u2f_counter;
 
 bool securechip_update_keys(void)
@@ -39,7 +44,7 @@ static const uint8_t _kdfkey[32] =
     "\xd2\xe1\xe6\xb1\x8b\x6c\x6b\x08\x43\x3e\xdb\xc1\xd1\x68\xc1\xa0\x04\x37\x74\xa4\x22\x18\x77"
     "\xe7\x9e\xd5\x66\x84\xbe\x5a\xc0\x1b";
 
-int securechip_kdf(securechip_slot_t slot, const uint8_t* msg, size_t len, uint8_t* kdf_out)
+static int _securechip_kdf(securechip_slot_t slot, const uint8_t* msg, size_t len, uint8_t* kdf_out)
 {
     const uint8_t* key;
     switch (slot) {
@@ -55,6 +60,14 @@ int securechip_kdf(securechip_slot_t slot, const uint8_t* msg, size_t len, uint8
     wally_hmac_sha256(key, 32, msg, len, kdf_out, 32);
     return 0;
 }
+int securechip_kdf(const uint8_t* msg, size_t len, uint8_t* kdf_out)
+{
+    return _securechip_kdf(SECURECHIP_SLOT_KDF, msg, len, kdf_out);
+}
+int securechip_kdf_rollkey(const uint8_t* msg, size_t len, uint8_t* kdf_out)
+{
+    return _securechip_kdf(SECURECHIP_SLOT_ROLLKEY, msg, len, kdf_out);
+}
 
 bool securechip_u2f_counter_set(uint32_t counter)
 {

test/unit-test/framework/mock_securechip.c

@@ -23,6 +23,11 @@
 #include <string.h>
 #include <wally_crypto.h>
 
+typedef enum {
+    SECURECHIP_SLOT_ROLLKEY = 3,
+    SECURECHIP_SLOT_KDF = 4,
+} securechip_slot_t;
+
 static uint32_t _u2f_counter;
 
 bool securechip_update_keys(void)
@@ -40,7 +45,7 @@ static const uint8_t _kdfkey[32] =
     "\xd2\xe1\xe6\xb1\x8b\x6c\x6b\x08\x43\x3e\xdb\xc1\xd1\x68\xc1\xa0\x04\x37\x74\xa4\x22\x18\x77"
     "\xe7\x9e\xd5\x66\x84\xbe\x5a\xc0\x1b";
 
-int securechip_kdf(securechip_slot_t slot, const uint8_t* msg, size_t len, uint8_t* kdf_out)
+static int _securechip_kdf(securechip_slot_t slot, const uint8_t* msg, size_t len, uint8_t* kdf_out)
 {
     const uint8_t* key;
     switch (slot) {
@@ -56,6 +61,14 @@ int securechip_kdf(securechip_slot_t slot, const uint8_t* msg, size_t len, uint8
     wally_hmac_sha256(key, 32, msg, len, kdf_out, 32);
     return 0;
 }
+int securechip_kdf(const uint8_t* msg, size_t len, uint8_t* kdf_out)
+{
+    return _securechip_kdf(SECURECHIP_SLOT_KDF, msg, len, kdf_out);
+}
+int securechip_kdf_rollkey(const uint8_t* msg, size_t len, uint8_t* kdf_out)
+{
+    return _securechip_kdf(SECURECHIP_SLOT_ROLLKEY, msg, len, kdf_out);
+}
 
 bool securechip_u2f_counter_set(uint32_t counter)
 {