bootutil: Provide support for embedded AES keys

de-nordic · de-nordic · commit 206c01aaa68c · 2025-10-23T15:24:43.000Z
Commit provides support for MCUBOOT_BUILTIN_ENC_KEY config
option, that allows to compile code with embedded key.
When this option is enabled, compilation requires
definition of boot_take_enc_key function to be provided by user;
prototype for the function is provided.

The boot_take_enc_key function is supposed to provide encryption
AES key to be used for image encryption and decryption.

Signed-off-by: Dominik Ermel &lt;dominik.ermel@nordicsemi.no&gt;
diff --git a/boot/boot_serial/src/boot_serial_encryption.c b/boot/boot_serial/src/boot_serial_encryption.c
@@ -235,7 +235,11 @@ decrypt_image_inplace(const struct flash_area *fa_p,
 #endif
         memset(&boot_data, 0, sizeof(struct boot_loader_state));
         /* Load the encryption keys into cache */
+#if !defined(MCUBOOT_BUILTIN_ENC_KEY)
         rc = boot_enc_load(state, BOOT_SLOT_PRIMARY, hdr, fa_p, bs);
+#else
+        rc = boot_take_enc_key(bs->enckey[BOOT_SLOT_PRIMARY], BOOT_CURR_IMG(state), BOOT_SLOT_PRIMARY);
+#endif
         if (rc < 0) {
             FIH_RET(fih_rc);
         }
diff --git a/boot/bootutil/include/bootutil/enc_key.h b/boot/bootutil/include/bootutil/enc_key.h
@@ -75,6 +75,9 @@ void boot_enc_decrypt(struct enc_key_data *enc_state,
 /* Note that boot_enc_zeorize takes BOOT_CURR_ENC, not BOOT_CURR_ENC_SLOT */
 void boot_enc_zeroize(struct enc_key_data *enc_state);
 
+/* Retrieve key for a slot */
+int boot_take_enc_key(uint8_t *key, int image, int slot);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/boot/bootutil/src/bootutil_misc.c b/boot/bootutil/src/bootutil_misc.c
@@ -386,7 +386,7 @@ boot_read_unprotected_tlv_sizes(const struct flash_area *fap, uint16_t *tlv_size
 }
 #endif
 
-#ifdef MCUBOOT_ENC_IMAGES
+#if defined(MCUBOOT_ENC_IMAGES) && !defined(MCUBOOT_BUILTIN_ENC_KEY)
 int
 boot_read_enc_key(const struct flash_area *fap, uint8_t slot, struct boot_status *bs)
 {
diff --git a/boot/bootutil/src/encrypted.c b/boot/bootutil/src/encrypted.c
@@ -370,6 +370,7 @@ static int fake_rng(void *p_rng, unsigned char *output, size_t len)
 #endif /* (MCUBOOT_ENCRYPT_RSA && MCUBOOT_USE_MBED_TLS && !MCUBOOT_USE_PSA_CRYPTO) ||
           (MCUBOOT_ENCRYPT_EC256 && MCUBOOT_USE_MBED_TLS) */
 
+#if !defined(MCUBOOT_BUILTIN_ENC_KEY)
 /*
  * Decrypt an encryption key TLV.
  *
@@ -564,7 +565,9 @@ boot_decrypt_key(const uint8_t *buf, uint8_t *enckey)
     return rc;
 }
 #endif /* CONFIG_BOOT_ED25519_PSA  && CONFIG_BOOT_ECDSA_PSA */
+#endif /* defined(MCUBOOT_BUILTIN_ENC_KEY) */
 
+#if !defined(MCUBOOT_BUILTIN_ENC_KEY)
 /*
  * Load encryption key.
  */
@@ -625,6 +628,7 @@ boot_enc_load(struct boot_loader_state *state, int slot,
 
     return boot_decrypt_key(buf, bs->enckey[slot]);
 }
+#endif /* defined(MCUBOOT_BUILTIN_ENC_KEY */
 
 int
 boot_enc_init(struct enc_key_data *enc_state)
diff --git a/boot/bootutil/src/loader.c b/boot/bootutil/src/loader.c
@@ -629,6 +629,7 @@ boot_image_check(struct boot_loader_state *state, struct image_header *hdr,
     int rc;
     FIH_DECLARE(fih_rc, FIH_FAILURE);
 
+    BOOT_LOG_DBG("boot_image_check");
 #if (BOOT_IMAGE_NUMBER == 1)
     (void)state;
 #endif
@@ -641,7 +642,11 @@ boot_image_check(struct boot_loader_state *state, struct image_header *hdr,
      */
 #if defined(MCUBOOT_ENC_IMAGES) && !defined(MCUBOOT_RAM_LOAD)
     if (MUST_DECRYPT(fap, BOOT_CURR_IMG(state), hdr)) {
+#if !defined(MCUBOOT_BUILTIN_ENC_KEY)
         rc = boot_enc_load(state, BOOT_SLOT_SECONDARY, hdr, fap, bs);
+#else
+        rc = boot_take_enc_key(bs->enckey[BOOT_SLOT_SECONDARY], BOOT_CURR_IMG(state), BOOT_SLOT_SECONDARY);
+#endif
         if (rc < 0) {
             FIH_RET(fih_rc);
         }
@@ -932,6 +937,7 @@ boot_validate_slot(struct boot_loader_state *state, int slot,
     }
 #endif
     if (!boot_is_header_valid(hdr, fap, state)) {
+        BOOT_LOG_DBG("boot_validate_slot: header validation failed %d", slot);
         fih_rc = FIH_FAILURE;
     } else {
         BOOT_HOOK_CALL_FIH(boot_image_check_hook, FIH_BOOT_HOOK_REGULAR,
@@ -944,16 +950,16 @@ boot_validate_slot(struct boot_loader_state *state, int slot,
 check_validity:
 #endif
     if (FIH_NOT_EQ(fih_rc, FIH_SUCCESS)) {
+#if !defined(__BOOTSIM__)
+        BOOT_LOG_ERR("Image in the %s slot is not valid!",
+                     (slot == BOOT_SLOT_PRIMARY) ? "primary" : "secondary");
+#endif
         if ((slot != BOOT_SLOT_PRIMARY) || ARE_SLOTS_EQUIVALENT()) {
             boot_scramble_slot(fap, slot);
             /* Image is invalid, erase it to prevent further unnecessary
              * attempts to validate and boot it.
              */
         }
-#if !defined(__BOOTSIM__)
-        BOOT_LOG_ERR("Image in the %s slot is not valid!",
-                     (slot == BOOT_SLOT_PRIMARY) ? "primary" : "secondary");
-#endif
         fih_rc = FIH_NO_BOOTABLE_IMAGE;
         goto out;
     }
@@ -1490,8 +1496,12 @@ boot_copy_image(struct boot_loader_state *state, struct boot_status *bs)
 #ifdef MCUBOOT_ENC_IMAGES
     if (IS_ENCRYPTED(boot_img_hdr(state, BOOT_SLOT_SECONDARY))) {
         rc = boot_enc_load(state, BOOT_SLOT_SECONDARY,
+#if !defined(MCUBOOT_BUILTIN_ENC_KEY)
                 boot_img_hdr(state, BOOT_SLOT_SECONDARY),
                 fap_secondary_slot, bs);
+#else
+        rc = boot_take_enc_key(bs->enckey[BOOT_SLOT_SECONDARY], BOOT_CURR_IMG(state), BOOT_SLOT_SECONDARY);
+#endif
 
         if (rc < 0) {
             return BOOT_EBADIMAGE;
@@ -1587,8 +1597,10 @@ boot_swap_image(struct boot_loader_state *state, struct boot_status *bs)
     struct image_header *hdr;
     const struct flash_area *fap;
 #ifdef MCUBOOT_ENC_IMAGES
+#ifndef MCUBOOT_BUILTIN_ENC_KEY
+    int i;
+#endif
     uint8_t slot;
-    uint8_t i;
 #endif
     uint32_t size;
     uint32_t copy_size;
@@ -1614,7 +1626,11 @@ boot_swap_image(struct boot_loader_state *state, struct boot_status *bs)
 #ifdef MCUBOOT_ENC_IMAGES
         if (IS_ENCRYPTED(hdr)) {
             fap = BOOT_IMG_AREA(state, BOOT_SLOT_PRIMARY);
+#if !defined(MCUBOOT_BUILTIN_ENC_KEY)
             rc = boot_enc_load(state, BOOT_SLOT_PRIMARY, hdr, fap, bs);
+#else
+            rc = boot_take_enc_key(bs->enckey[BOOT_SLOT_PRIMARY], BOOT_CURR_IMG(state), BOOT_SLOT_PRIMARY);
+#endif
             assert(rc >= 0);
 
             if (rc == 0) {
@@ -1638,7 +1654,11 @@ boot_swap_image(struct boot_loader_state *state, struct boot_status *bs)
         hdr = boot_img_hdr(state, BOOT_SLOT_SECONDARY);
         if (IS_ENCRYPTED(hdr)) {
             fap = BOOT_IMG_AREA(state, BOOT_SLOT_SECONDARY);
+#if !defined(MCUBOOT_BUILTIN_ENC_KEY)
             rc = boot_enc_load(state, BOOT_SLOT_SECONDARY, hdr, fap, bs);
+#else
+            rc = boot_take_enc_key(bs->enckey[BOOT_SLOT_SECONDARY], BOOT_CURR_IMG(state), BOOT_SLOT_SECONDARY);
+#endif
             assert(rc >= 0);
 
             if (rc == 0) {
@@ -1675,6 +1695,7 @@ boot_swap_image(struct boot_loader_state *state, struct boot_status *bs)
 
             boot_enc_init(BOOT_CURR_ENC_SLOT(state, slot));
 
+#ifndef MCUBOOT_BUILTIN_ENC_KEY
             rc = boot_read_enc_key(fap, slot, bs);
             assert(rc == 0);
 
@@ -1684,9 +1705,15 @@ boot_swap_image(struct boot_loader_state *state, struct boot_status *bs)
                 }
             }
 
-            if (i != BOOT_ENC_KEY_SIZE) {
-                boot_enc_set_key(BOOT_CURR_ENC_SLOT(state, slot), bs->enckey[slot]);
+            if (i == BOOT_ENC_KEY_SIZE) {
+                /* Invalid key */
+                continue;
             }
+#else
+            rc = boot_take_enc_key(bs->enckey[slot], image_index, slot);
+            assert(rc == 0);
+#endif
+            boot_enc_set_key(BOOT_CURR_ENC_SLOT(state, slot), bs->enckey[slot]);
         }
 #endif
         flash_area_close(fap);
diff --git a/boot/mynewt/src/single_loader.c b/boot/mynewt/src/single_loader.c
@@ -49,6 +49,7 @@ boot_image_validate(const struct flash_area *fa_p,
          * was performed. We will try to validate the image, and if still
          * encrypted the validation will fail, and go in panic mode
          */
+        BOOT_LOG_DBG("boot_image_validate: clearing encryption flags");
         hdr->ih_flags &= ~(ENCRYPTIONFLAGS);
     }
     FIH_CALL(bootutil_img_validate, fih_rc, NULL, hdr, fa_p, tmpbuf,

Original file line number	Diff line number	Diff line change
`@@ -75,6 +75,9 @@ void boot_enc_decrypt(struct enc_key_data *enc_state,`
`75`	`75`	`/* Note that boot_enc_zeorize takes BOOT_CURR_ENC, not BOOT_CURR_ENC_SLOT */`
`76`	`76`	`void boot_enc_zeroize(struct enc_key_data *enc_state);`
`77`	`77`
	`78`	`+/* Retrieve key for a slot */`
	`79`	`+int boot_take_enc_key(uint8_t *key, int image, int slot);`
	`80`	`+`
`78`	`81`	`#ifdef __cplusplus`
`79`	`82`	`}`
`80`	`83`	`#endif`
Original file line number	Diff line number	Diff line change
`@@ -386,7 +386,7 @@ boot_read_unprotected_tlv_sizes(const struct flash_area fap, uint16_t tlv_size`
`386`	`386`	`}`
`387`	`387`	`#endif`
`388`	`388`
`389`		`-#ifdef MCUBOOT_ENC_IMAGES`
	`389`	`+#if defined(MCUBOOT_ENC_IMAGES) && !defined(MCUBOOT_BUILTIN_ENC_KEY)`
`390`	`390`	`int`
`391`	`391`	`boot_read_enc_key(const struct flash_area fap, uint8_t slot, struct boot_status bs)`
`392`	`392`	`{`
Original file line number	Diff line number	Diff line change
`@@ -49,6 +49,7 @@ boot_image_validate(const struct flash_area *fa_p,`
`49`	`49`	`* was performed. We will try to validate the image, and if still`
`50`	`50`	`* encrypted the validation will fail, and go in panic mode`
`51`	`51`	`*/`
	`52`	`+ BOOT_LOG_DBG("boot_image_validate: clearing encryption flags");`
`52`	`53`	`hdr->ih_flags &= ~(ENCRYPTIONFLAGS);`
`53`	`54`	`}`
`54`	`55`	`FIH_CALL(bootutil_img_validate, fih_rc, NULL, hdr, fa_p, tmpbuf,`