bootutil: Provide support for embedded AES keys

Commit provides support for MCUBOOT_EMBEDDED_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 <dominik.ermel@nordicsemi.no>

Author: de-nordic

boot/boot_serial/src/boot_serial_encryption.c

@@ -31,7 +31,11 @@ boot_image_validate_encrypted(struct boot_loader_state *state,
     int rc;
 
     if (MUST_DECRYPT(fa_p, BOOT_CURR_IMG(state), hdr)) {
+#ifdef MCUBOOT_EMBEDDED_ENC_KEY
+        rc = boot_en_take_key(bs->enckey[BOOT_SLOT_SECONDARY], BOOT_CUR_IMG(state), BOOT_SLOT_SECONDARY);
+#else
         rc = boot_enc_load(state, BOOT_SLOT_SECONDARY, hdr, fa_p, bs);
+#endif
         if (rc < 0) {
             FIH_RET(fih_rc);
         }
@@ -232,7 +236,11 @@ decrypt_image_inplace(const struct flash_area *fa_p,
         }
 #endif
         /* Load the encryption keys into cache */
+#ifdef MCUBOOT_EMBEDDED_ENC_KEY
+        rc = boot_take_enc_key(bs->enckey[BOOT_SLOT_PRIMARY], BOOT_CURR_IMG(state), BOOT_SLOT_PRIMARY);
+#else
         rc = boot_enc_load(state, BOOT_SLOT_PRIMARY, hdr, fa_p, bs);
+#endif
         if (rc < 0) {
             goto total_out;
         }

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

boot/bootutil/src/bootutil_loader.c

@@ -179,7 +179,11 @@ boot_check_image(struct boot_loader_state *state, struct boot_status *bs, int sl
      */
 #if defined(MCUBOOT_ENC_IMAGES) && !defined(MCUBOOT_RAM_LOAD)
     if (MUST_DECRYPT(fap, BOOT_CURR_IMG(state), hdr)) {
+#ifdef MCUBOOT_EMBEDDED_ENC_KEY
+        rc = boot_take_enc_key(bs->enckey[BOOT_SLOT_SECONDARY], BOOT_CURR_IMG(state), BOOT_SLOT_SECONDARY);
+#else
         rc = boot_enc_load(state, BOOT_SLOT_SECONDARY, hdr, fap, bs);
+#endif
         if (rc < 0) {
             FIH_RET(fih_rc);
         }

boot/bootutil/src/bootutil_misc.c

@@ -239,7 +239,7 @@ 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_EMBEDDED_ENC_KEY)
 int
 boot_read_enc_key(const struct flash_area *fap, uint8_t slot, struct boot_status *bs)
 {

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_EMBEDDED_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_EMBEDDED_ENC_KEY) */
 
+#if !defined(MCUBOOT_EMBEDDED_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_EMBEDDED_ENC_KEY */
 
 int
 boot_enc_init(struct enc_key_data *enc_state)

boot/bootutil/src/loader.c

@@ -1006,9 +1006,13 @@ 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))) {
+#ifdef MCUBOOT_EMBEDDED_ENC_KEY
+        rc = boot_take_enc_key(bs->enckey[BOOT_SLOT_SECONDARY], BOOT_CURR_IMG(state), BOOT_SLOT_SECONDARY);
+#else
         rc = boot_enc_load(state, BOOT_SLOT_SECONDARY,
                 boot_img_hdr(state, BOOT_SLOT_SECONDARY),
                 fap_secondary_slot, bs);
+#endif /* MCUBOOT_EMBEDDED_ENC_KEY */
 
         if (rc < 0) {
             return BOOT_EBADIMAGE;
@@ -1130,7 +1134,11 @@ 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);
+#ifdef MCUBOOT_EMBEDDED_ENC_KEY
+            rc = boot_take_enc_key(bs->enckey[BOOT_SLOT_PRIMARY], BOOT_CURR_IMG(state), BOOT_SLOT_PRIMARY);
+#else
             rc = boot_enc_load(state, BOOT_SLOT_PRIMARY, hdr, fap, bs);
+#endif /* MCUBOOT_EMBEDDED_ENC_KEY */
             assert(rc >= 0);
 
             if (rc == 0) {
@@ -1154,7 +1162,11 @@ 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);
+#ifdef MCUBOOT_EMBEDDED_ENC_KEY
+            rc = boot_take_enc_key(bs->enckey[BOOT_SLOT_SECONDARY], BOOT_CURR_IMG(state), BOOT_SLOT_SECONDARY);
+#else
             rc = boot_enc_load(state, BOOT_SLOT_SECONDARY, hdr, fap, bs);
+#endif /* MCUBOOT_EMBEDDED_ENC_KEY */
             assert(rc >= 0);
 
             if (rc == 0) {
@@ -1191,15 +1203,19 @@ boot_swap_image(struct boot_loader_state *state, struct boot_status *bs)
 
             boot_enc_init(BOOT_CURR_ENC_SLOT(state, slot));
 
+#ifdef MCUBOOT_EMBEDDED_ENC_KEY
+            rc = boot_take_enc_key(bs->enckey[slot], image_index, slot);
+#else
             rc = boot_read_enc_key(fap, slot, bs);
+#endif /* MCUBOOT_EMBEDDED_ENC_KEY */
             if (rc) {
                 BOOT_LOG_DBG("boot_swap_image: Failed loading key (%d, %d)",
                               image_index, slot);
             } else {
                 boot_enc_set_key(BOOT_CURR_ENC_SLOT(state, slot), bs->enckey[slot]);
             }
         }
-#endif
+#endif /* MCUBOOT_ENC_IMAGES */
         flash_area_close(fap);
     }
 

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,