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Making key decryption nicer #2328

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Making key decryption nicer #2328

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70531a7
Decrypt_key: One context, common defs
de-nordic May 30, 2025
6c2bbf0
Hkdf uses size_t
de-nordic May 30, 2025
57aa87e
bootutil: Enc uses one context type for key exchange
de-nordic Jun 17, 2025
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1 change: 1 addition & 0 deletions boot/bootutil/include/bootutil/crypto/ecdh_p256.h
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Original file line number Diff line number Diff line change
Expand Up @@ -35,6 +35,7 @@ extern "C" {

#if defined(MCUBOOT_USE_TINYCRYPT)
typedef uintptr_t bootutil_ecdh_p256_context;
typedef bootutil_ecdh_p256_context bootutil_key_xchange_ctx;
static inline void bootutil_ecdh_p256_init(bootutil_ecdh_p256_context *ctx)
{
(void)ctx;
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1 change: 1 addition & 0 deletions boot/bootutil/include/bootutil/crypto/ecdh_x25519.h
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Expand Up @@ -26,6 +26,7 @@ extern int X25519(uint8_t out_shared_key[32], const uint8_t private_key[32],
const uint8_t peer_public_value[32]);

typedef uintptr_t bootutil_ecdh_x25519_context;
typedef bootutil_ecdh_x25519_context bootutil_key_xchange_ctx;
static inline void bootutil_ecdh_x25519_init(bootutil_ecdh_x25519_context *ctx)
{
(void)ctx;
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2 changes: 2 additions & 0 deletions boot/bootutil/include/bootutil/crypto/rsa.h
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Expand Up @@ -68,6 +68,7 @@ extern "C" {
typedef struct {
psa_key_id_t key_id;
} bootutil_rsa_context;
typedef bootutil_rsa_context bootutil_key_xchange_ctx;

static inline void bootutil_rsa_init(bootutil_rsa_context *ctx)
{
Expand Down Expand Up @@ -176,6 +177,7 @@ static inline int bootutil_rsassa_pss_verify(const bootutil_rsa_context *ctx,
#elif defined(MCUBOOT_USE_MBED_TLS)

typedef mbedtls_rsa_context bootutil_rsa_context;
typedef bootutil_rsa_context bootutil_key_xchange_ctx;

static inline void bootutil_rsa_init(bootutil_rsa_context *ctx)
{
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65 changes: 25 additions & 40 deletions boot/bootutil/src/encrypted.c
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Expand Up @@ -264,15 +264,15 @@ parse_x25519_enckey(uint8_t **p, uint8_t *end, uint8_t *private_key)
* @param okm_len On input the requested length; on output the generated length
*/
static int
hkdf(uint8_t *ikm, uint16_t ikm_len, uint8_t *info, uint16_t info_len,
uint8_t *okm, uint16_t *okm_len)
hkdf(const uint8_t *ikm, size_t ikm_len, const uint8_t *info, size_t info_len,
uint8_t *okm, size_t *okm_len)
{
bootutil_hmac_sha256_context hmac;
uint8_t salt[BOOTUTIL_CRYPTO_SHA256_DIGEST_SIZE];
uint8_t prk[BOOTUTIL_CRYPTO_SHA256_DIGEST_SIZE];
uint8_t T[BOOTUTIL_CRYPTO_SHA256_DIGEST_SIZE];
uint16_t off;
uint16_t len;
size_t off;
size_t len;
uint8_t counter;
bool first;
int rc;
Expand Down Expand Up @@ -405,29 +405,20 @@ static int fake_rng(void *p_rng, unsigned char *output, size_t len)
int
boot_decrypt_key(const uint8_t *buf, uint8_t *enckey)
{
#if defined(MCUBOOT_ENCRYPT_RSA)
bootutil_rsa_context rsa;
uint8_t *cp;
uint8_t *cpend;
size_t olen;
#endif
#if defined(MCUBOOT_ENCRYPT_EC256)
bootutil_ecdh_p256_context ecdh_p256;
#endif
#if defined(MCUBOOT_ENCRYPT_X25519)
bootutil_ecdh_x25519_context ecdh_x25519;
#endif
bootutil_key_xchange_ctx pk_ctx;
#if defined(MCUBOOT_ENCRYPT_EC256) || defined(MCUBOOT_ENCRYPT_X25519)
bootutil_hmac_sha256_context hmac;
bootutil_aes_ctr_context aes_ctr;
uint8_t tag[BOOTUTIL_CRYPTO_SHA256_DIGEST_SIZE];
uint8_t shared[SHARED_KEY_LEN];
uint8_t derived_key[BOOT_ENC_KEY_SIZE + BOOTUTIL_CRYPTO_SHA256_DIGEST_SIZE];
uint8_t *cp;
uint8_t *cpend;
uint8_t private_key[PRIV_KEY_LEN];
uint8_t counter[BOOT_ENC_BLOCK_SIZE];
uint16_t len;
#endif
#if !defined(MCUBOOT_ENCRYPT_KW)
uint8_t *cp;
uint8_t *cpend;
size_t len;
#endif
struct bootutil_key *bootutil_enc_key = NULL;
int rc = -1;
Expand All @@ -441,21 +432,23 @@ boot_decrypt_key(const uint8_t *buf, uint8_t *enckey)
return rc;
}

#if defined(MCUBOOT_ENCRYPT_RSA)

bootutil_rsa_init(&rsa);
#if !defined(MCUBOOT_ENCRYPT_KW)
cp = (uint8_t *)bootutil_enc_key->key;
cpend = cp + *bootutil_enc_key->len;
#endif

#if defined(MCUBOOT_ENCRYPT_RSA)
bootutil_rsa_init(&pk_ctx);

/* The enckey is encrypted through RSA so for decryption we need the private key */
rc = bootutil_rsa_parse_private_key(&rsa, &cp, cpend);
rc = bootutil_rsa_parse_private_key(&pk_ctx, &cp, cpend);
if (rc) {
bootutil_rsa_drop(&rsa);
bootutil_rsa_drop(&pk_ctx);
return rc;
}

rc = bootutil_rsa_oaep_decrypt(&rsa, &olen, buf, enckey, BOOT_ENC_KEY_SIZE);
bootutil_rsa_drop(&rsa);
rc = bootutil_rsa_oaep_decrypt(&pk_ctx, &len, buf, enckey, BOOT_ENC_KEY_SIZE);
bootutil_rsa_drop(&pk_ctx);
if (rc) {
return rc;
}
Expand All @@ -470,10 +463,6 @@ boot_decrypt_key(const uint8_t *buf, uint8_t *enckey)
#endif /* defined(MCUBOOT_ENCRYPT_KW) */

#if defined(MCUBOOT_ENCRYPT_EC256)

cp = (uint8_t *)bootutil_enc_key->key;
cpend = cp + *bootutil_enc_key->len;

/*
* Load the stored EC256 decryption private key
*/
Expand All @@ -486,21 +475,17 @@ boot_decrypt_key(const uint8_t *buf, uint8_t *enckey)
/*
* First "element" in the TLV is the curve point (public key)
*/
bootutil_ecdh_p256_init(&ecdh_p256);
bootutil_ecdh_p256_init(&pk_ctx);

rc = bootutil_ecdh_p256_shared_secret(&ecdh_p256, &buf[EC_PUBK_INDEX], private_key, shared);
bootutil_ecdh_p256_drop(&ecdh_p256);
rc = bootutil_ecdh_p256_shared_secret(&pk_ctx, &buf[EC_PUBK_INDEX], private_key, shared);
bootutil_ecdh_p256_drop(&pk_ctx);
if (rc != 0) {
return -1;
}

#endif /* defined(MCUBOOT_ENCRYPT_EC256) */

#if defined(MCUBOOT_ENCRYPT_X25519)

cp = (uint8_t *)bootutil_enc_key->key;
cpend = cp + *bootutil_enc_key->len;

/*
* Load the stored X25519 decryption private key
*/
Expand All @@ -514,10 +499,10 @@ boot_decrypt_key(const uint8_t *buf, uint8_t *enckey)
* First "element" in the TLV is the curve point (public key)
*/

bootutil_ecdh_x25519_init(&ecdh_x25519);
bootutil_ecdh_x25519_init(&pk_ctx);

rc = bootutil_ecdh_x25519_shared_secret(&ecdh_x25519, &buf[EC_PUBK_INDEX], private_key, shared);
bootutil_ecdh_x25519_drop(&ecdh_x25519);
rc = bootutil_ecdh_x25519_shared_secret(&pk_ctx, &buf[EC_PUBK_INDEX], private_key, shared);
bootutil_ecdh_x25519_drop(&pk_ctx);
if (!rc) {
return -1;
}
Expand Down
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