From e94cd203e159f97edc641f0d2245ff7be002464d Mon Sep 17 00:00:00 2001 From: Dominik Ermel Date: Tue, 8 Oct 2024 16:31:48 +0000 Subject: [PATCH] bootutil: Allow bypassing ASN.1 encoding for ED25519 key import The commit adds MCUBOOT_KEY_IMPORT_BYPASS_ASN configuration option that allows bypassing ASN.1 decoding of ED25519 public key, compiled into MCUboot. When the option is enabled the key will be accessed directly and ASN.1 processing is not compiled in, resulting in smaller footprint of MCUboot, at a cost of reduced detection of invalid key, i.e. public key designated for different method than compiled in. Signed-off-by: Dominik Ermel --- boot/bootutil/src/image_ed25519.c | 19 ++++++++++++++++++- .../include/mcuboot_config/mcuboot_config.h | 4 ++++ 2 files changed, 22 insertions(+), 1 deletion(-) diff --git a/boot/bootutil/src/image_ed25519.c b/boot/bootutil/src/image_ed25519.c index 40d494bcf..93fd5de88 100644 --- a/boot/bootutil/src/image_ed25519.c +++ b/boot/bootutil/src/image_ed25519.c @@ -26,16 +26,18 @@ #define EDDSA_SIGNATURE_LENGTH 64 -static const uint8_t ed25519_pubkey_oid[] = MBEDTLS_OID_ISO_IDENTIFIED_ORG "\x65\x70"; #define NUM_ED25519_BYTES 32 extern int ED25519_verify(const uint8_t *message, size_t message_len, const uint8_t signature[EDDSA_SIGNATURE_LENGTH], const uint8_t public_key[NUM_ED25519_BYTES]); +#if !defined(MCUBOOT_KEY_IMPORT_BYPASS_ASN) /* * Parse the public key used for signing. */ +static const uint8_t ed25519_pubkey_oid[] = MBEDTLS_OID_ISO_IDENTIFIED_ORG "\x65\x70"; + static int bootutil_import_key(uint8_t **cp, uint8_t *end) { @@ -71,6 +73,7 @@ bootutil_import_key(uint8_t **cp, uint8_t *end) return 0; } +#endif /* !defined(MCUBOOT_KEY_IMPORT_BYPASS_ASN) */ fih_ret bootutil_verify_sig(uint8_t *hash, uint32_t hlen, uint8_t *sig, size_t slen, @@ -89,11 +92,25 @@ bootutil_verify_sig(uint8_t *hash, uint32_t hlen, uint8_t *sig, size_t slen, pubkey = (uint8_t *)bootutil_keys[key_id].key; end = pubkey + *bootutil_keys[key_id].len; +#if !defined(MCUBOOT_KEY_IMPORT_BYPASS_ASN) rc = bootutil_import_key(&pubkey, end); if (rc) { FIH_SET(fih_rc, FIH_FAILURE); goto out; } +#else + /* Directly use the key contents from the ASN stream, + * these are the last NUM_ED25519_BYTES. + * There is no check whether this is the correct key, + * here, by the algorithm selected. + */ + if (*bootutil_keys[key_id].len < NUM_ED25519_BYTES) { + FIH_SET(fih_rc, FIH_FAILURE); + goto out; + } + + pubkey = end - NUM_ED25519_BYTES; +#endif rc = ED25519_verify(hash, IMAGE_HASH_SIZE, sig, pubkey); diff --git a/boot/zephyr/include/mcuboot_config/mcuboot_config.h b/boot/zephyr/include/mcuboot_config/mcuboot_config.h index 7896e0939..bc5188138 100644 --- a/boot/zephyr/include/mcuboot_config/mcuboot_config.h +++ b/boot/zephyr/include/mcuboot_config/mcuboot_config.h @@ -34,6 +34,10 @@ # error "One crypto library implementation allowed at a time." #endif +#if defined(CONFIG_BOOT_KEY_IMPORT_BYPASS_ASN) +#define MCUBOOT_KEY_IMPORT_BYPASS_ASN +#endif + #ifdef CONFIG_BOOT_USE_MBEDTLS #define MCUBOOT_USE_MBED_TLS #elif defined(CONFIG_BOOT_USE_TINYCRYPT)