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Allow bypasing signature hash key matching #2310

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5be772e
bootutil: Support for MCUBOOT_BYPASS_KEY_MATCH
de-nordic May 15, 2025
b8d1214
zephyr: Add CONFIG_BOOT_BYPASS_KEY_MATCH
de-nordic May 15, 2025
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14 changes: 14 additions & 0 deletions boot/bootutil/src/image_validate.c
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Original file line number Diff line number Diff line change
Expand Up @@ -278,6 +278,8 @@ bootutil_img_hash(struct boot_loader_state *state,
# define KEY_BUF_SIZE (SIG_BUF_SIZE + 24)
#endif /* !MCUBOOT_HW_KEY */

#if !defined(MCUBOOT_BYPASS_KEY_MATCH)
/* Find functions are only needed when key is checked first */
#if !defined(MCUBOOT_HW_KEY)
static int
bootutil_find_key(uint8_t *keyhash, uint8_t keyhash_len)
Expand Down Expand Up @@ -347,6 +349,18 @@ bootutil_find_key(uint8_t image_index, uint8_t *key, uint16_t key_len)
#endif /* !MCUBOOT_HW_KEY */
#endif /* !MCUBOOT_BUILTIN_KEY */
#endif /* EXPECTED_SIG_TLV */
#else /* !MCUBOOT_BYPASS_KEY_MATCH */
static inline int
bootutil_find_key(uint8_t image_index, uint8_t *key, uint16_t key_len)
{
(void)image_index;
(void)key;
(void)key_len;

/* There is only one key, so it always matches */
return 0;
}
#endif /* !MCUBOOT_BYPASS_KEY_MATCH */

/**
* Reads the value of an image's security counter.
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13 changes: 13 additions & 0 deletions boot/zephyr/Kconfig
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Expand Up @@ -325,6 +325,19 @@ endif

endchoice

config BOOT_BYPASS_KEY_MATCH
bool "Do not match TLV key hash against built in key"
depends on !BOOT_SIGNATURE_TYPE_NONE
depends on !BOOT_HW_KEY
help
MCUboot reads, from TLV, hash of a key that should be used to verify
a signature and uses it to find a builtin key.
This action is pointless when there is single key compiled in,
as the signature verification process will just fail if that is not
the right key.
Enabling this option turns off key matching, slightly reducing
MCUboot code and boot time.

config BOOT_SIGNATURE_KEY_FILE
string "PEM key file"
default "root-ec-p256.pem" if BOOT_SIGNATURE_TYPE_ECDSA_P256
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9 changes: 9 additions & 0 deletions boot/zephyr/include/mcuboot_config/mcuboot_config.h
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Original file line number Diff line number Diff line change
Expand Up @@ -164,6 +164,15 @@
#define MCUBOOT_HMAC_SHA512
#endif

/* Turn off check of public key hash against compiled in key
* before attempting signature verification. When there is only
* one key, matching is pointless, the signature may just be
* verified with the only key that there is.
*/
#ifdef CONFIG_BOOT_BYPASS_KEY_MATCH
#define MCUBOOT_BYPASS_KEY_MATCH
#endif

#ifdef CONFIG_BOOT_DECOMPRESSION
#define MCUBOOT_DECOMPRESS_IMAGES
#endif
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