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Allow bypassing ASN.1 processing of public key for ED25519 #2089

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Allow bypassing ASN.1 processing of public key for ED25519 #2089

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3bd36e1
bootutil: Allow bypassing ASN.1 encoding for ED25519 key import
de-nordic Oct 8, 2024
86e26fa
zephyr: Add Kconfig option CONFIG_BOOT_KEY_IMPORT_BYPASS_ASN
de-nordic Oct 8, 2024
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19 changes: 18 additions & 1 deletion boot/bootutil/src/image_ed25519.c
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Original file line number Diff line number Diff line change
Expand Up @@ -18,16 +18,18 @@
#include "bootutil_priv.h"
#include "bootutil/crypto/common.h"

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[64],
const uint8_t public_key[32]);

#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)
{
Expand Down Expand Up @@ -63,6 +65,7 @@ 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,
Expand All @@ -81,11 +84,25 @@ 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, 32, sig, pubkey);

Expand Down
9 changes: 9 additions & 0 deletions boot/zephyr/Kconfig
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Original file line number Diff line number Diff line change
Expand Up @@ -183,6 +183,15 @@ config BOOT_ED25519_MBEDTLS
select BOOT_USE_MBEDTLS
select MBEDTLS
endchoice

config BOOT_KEY_IMPORT_BYPASS_ASN
bool "Directly access key value without ASN.1 parsing"
help
Originally, public keys compiled into MCUboot were
stored in ASN.1 encoded format. Enabling this option
bypasses the ASN.1 decoding and directly accesses the key
in ASN.1 bitstream; this reduces MCUboot code by removing
the ASN.1 processing.
endif

endchoice
Expand Down
4 changes: 4 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 @@ -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)
Expand Down
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