Commit 1dcfbdac authored by Dominik Ermel's avatar Dominik Ermel Committed by Dávid Vincze
Browse files

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: default avatarDominik Ermel <dominik.ermel@nordicsemi.no>
parent f2b6def9

boot/bootutil/src/image_ed25519.c

+20 −2
Original line number Diff line number Diff line
@@ -13,27 +13,30 @@ 
#ifdef MCUBOOT_SIGN_ED25519

#include "bootutil/sign_key.h"



#if !defined(MCUBOOT_KEY_IMPORT_BYPASS_ASN)

/* We are not really using the MBEDTLS but need the ASN.1 parsing functions */

#define MBEDTLS_ASN1_PARSE_C

#include "mbedtls/oid.h"

#include "mbedtls/asn1.h"

#endif



#include "bootutil_priv.h"

#include "bootutil/crypto/common.h"

#include "bootutil/crypto/sha.h"



#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)

{
@@ -69,6 +72,7 @@ bootutil_import_key(uint8_t **cp, uint8_t *end) 


    return 0;

}

#endif /* !defined(MCUBOOT_KEY_IMPORT_BYPASS_ASN) */



/* Signature verification base function.

 * The function takes buffer of specified length and tries to verify
@@ -94,11 +98,25 @@ bootutil_verify(uint8_t *buf, uint32_t blen, 
    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(buf, blen, sig, pubkey);

boot/zephyr/include/mcuboot_config/mcuboot_config.h

+4 −0
Original line number Diff line number Diff line
@@ -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)

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