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Don't use pk_write in ecdsa_sign_wrap with USE_PSA_CRYPTO

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Under MBEDTLS_USE_PSA_CRYPTO, ecdsa_sign_wrap() was calling
mbedtls_pk_write_key_der() to write a private key in SEC1 format, only to
then extract the part that represents the private value which is what
psa_import_key() actually wants. Instead, call an mpi function to directly
get the private key in the desired format.

This slightly reduces the code size and stack usage, and removes a
dependency on pk_write.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2022-10-04 22:59:26 +02:00 committed by Valerio Setti
parent b4a87b07f8
commit 13caa94746
1 changed files with 11 additions and 71 deletions
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82
library/pk_wrap.c
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@ -869,54 +869,6 @@ static int pk_ecdsa_sig_asn1_from_psa(unsigned char *sig, size_t *sig_len,
return 0;
}
/* Locate an ECDSA privateKey in a RFC 5915, or SEC1 Appendix C.4 ASN.1 buffer
*
* [in/out] buf: ASN.1 buffer start as input - ECDSA privateKey start as output
* [in] end: ASN.1 buffer end
* [out] key_len: the ECDSA privateKey length in bytes
*/
static int find_ecdsa_private_key(unsigned char **buf, unsigned char *end,
size_t *key_len)
{
size_t len;
int ret;
/*
* RFC 5915, or SEC1 Appendix C.4
*
* ECPrivateKey ::= SEQUENCE {
* version INTEGER { ecPrivkeyVer1(1) } (ecPrivkeyVer1),
* privateKey OCTET STRING,
* parameters [0] ECParameters {{ NamedCurve }} OPTIONAL,
* publicKey [1] BIT STRING OPTIONAL
* }
*/
if ((ret = mbedtls_asn1_get_tag(buf, end, &len,
MBEDTLS_ASN1_CONSTRUCTED |
MBEDTLS_ASN1_SEQUENCE)) != 0) {
return ret;
}
/* version */
if ((ret = mbedtls_asn1_get_tag(buf, end, &len,
MBEDTLS_ASN1_INTEGER)) != 0) {
return ret;
}
*buf += len;
/* privateKey */
if ((ret = mbedtls_asn1_get_tag(buf, end, &len,
MBEDTLS_ASN1_OCTET_STRING)) != 0) {
return ret;
}
*key_len = len;
return 0;
}
static int ecdsa_sign_wrap(void *ctx_arg, mbedtls_md_type_t md_alg,
const unsigned char *hash, size_t hash_len,
unsigned char *sig, size_t sig_size, size_t *sig_len,
@ -927,19 +879,14 @@ static int ecdsa_sign_wrap(void *ctx_arg, mbedtls_md_type_t md_alg,
psa_key_attributes_t attributes = PSA_KEY_ATTRIBUTES_INIT;
mbedtls_svc_key_id_t key_id = MBEDTLS_SVC_KEY_ID_INIT;
psa_status_t status;
mbedtls_pk_context key;
size_t key_len;
unsigned char buf[MBEDTLS_PK_ECP_PRV_DER_MAX_BYTES];
unsigned char *p;
psa_algorithm_t psa_hash = mbedtls_hash_info_psa_from_md(md_alg);
#if defined(MBEDTLS_ECDSA_DETERMINISTIC)
psa_algorithm_t psa_sig_md = PSA_ALG_DETERMINISTIC_ECDSA(psa_hash);
#else
psa_algorithm_t psa_sig_md = PSA_ALG_ECDSA(psa_hash);
#endif
unsigned char buf[PSA_KEY_EXPORT_ECC_KEY_PAIR_MAX_SIZE(
PSA_VENDOR_ECC_MAX_CURVE_BITS )];
psa_algorithm_t psa_sig_md =
PSA_ALG_ECDSA( mbedtls_hash_info_psa_from_md( md_alg ) );
size_t curve_bits;
psa_ecc_family_t curve =
mbedtls_ecc_group_to_psa(ctx->grp.id, &curve_bits);
mbedtls_ecc_group_to_psa( ctx->grp.id, &curve_bits );
size_t key_len = PSA_BITS_TO_BYTES(curve_bits);
/* PSA has its own RNG */
((void) f_rng);
@ -949,18 +896,11 @@ static int ecdsa_sign_wrap(void *ctx_arg, mbedtls_md_type_t md_alg,
return MBEDTLS_ERR_PK_BAD_INPUT_DATA;
}
/* mbedtls_pk_write_key_der() expects a full PK context;
* re-construct one to make it happy */
key.pk_info = &mbedtls_eckey_info;
key.pk_ctx = ctx;
key_len = mbedtls_pk_write_key_der(&key, buf, sizeof(buf));
if (key_len <= 0) {
return MBEDTLS_ERR_PK_BAD_INPUT_DATA;
if (key_len > sizeof(buf)) {
return( MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED );
}
p = buf + sizeof(buf) - key_len;
ret = find_ecdsa_private_key(&p, buf + sizeof(buf), &key_len);
if (ret != 0) {
ret = mbedtls_mpi_write_binary(&ctx->d, buf, key_len);
if( ret != 0 ) {
goto cleanup;
}
@ -969,7 +909,7 @@ static int ecdsa_sign_wrap(void *ctx_arg, mbedtls_md_type_t md_alg,
psa_set_key_algorithm(&attributes, psa_sig_md);
status = psa_import_key(&attributes,
p, key_len,
buf, key_len,
&key_id);
if (status != PSA_SUCCESS) {
ret = mbedtls_pk_error_from_psa(status);