psa_util: improve convert_raw_to_der_single_int()
Allow the function to support DER buffers than what it is nominally
required by the provided coordinates. In other words let's ignore
padding zeros in the raw number.
Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/include/mbedtls/psa_util.h b/include/mbedtls/psa_util.h
index 06732d8..132c73f 100644
--- a/include/mbedtls/psa_util.h
+++ b/include/mbedtls/psa_util.h
@@ -191,7 +191,12 @@
* \param raw_len Length of \p raw in bytes.
* \param[out] der Buffer that will be filled with the converted DER
* output. It can overlap with raw buffer.
- * \param der_size Size of \p der in bytes.
+ * \param der_size Size of \p der in bytes. Given \p bits parameter:
+ * * #MBEDTLS_ECDSA_MAX_SIG_LEN(\p bits) can be used
+ * to determine a large enough buffer for any
+ * \p raw input vector.
+ * * The minimum size might be smaller in case
+ * \p raw input vector contains padding zeros.
* \param[out] der_len On success it contains the amount of valid data
* (in bytes) written to \p der. It's undefined
* in case of failure.
diff --git a/library/psa_util.c b/library/psa_util.c
index 2491f2e..4e350c0 100644
--- a/library/psa_util.c
+++ b/library/psa_util.c
@@ -365,9 +365,21 @@
unsigned char *der_buf_end)
{
unsigned char *p = der_buf_end;
- int len = (int) raw_len;
+ int len;
int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+ /* ASN.1 DER encoding requires minimal length, so skip leading 0s.
+ * Provided input MPIs should not be 0, but as a failsafe measure, still
+ * detect that and return error in case. */
+ while (*raw_buf == 0x00) {
+ ++raw_buf;
+ --raw_len;
+ if (raw_len == 0) {
+ return MBEDTLS_ERR_ASN1_INVALID_DATA;
+ }
+ }
+ len = (int) raw_len;
+
/* Copy the raw coordinate to the end of der_buf. */
if ((p - der_buf_start) < len) {
return MBEDTLS_ERR_ASN1_BUF_TOO_SMALL;
@@ -375,17 +387,6 @@
p -= len;
memcpy(p, raw_buf, len);
- /* ASN.1 DER encoding requires minimal length, so skip leading 0s.
- * Provided input MPIs should not be 0, but as a failsafe measure, still
- * detect that and return error in case. */
- while (*p == 0x00) {
- ++p;
- --len;
- if (len == 0) {
- return MBEDTLS_ERR_ASN1_INVALID_DATA;
- }
- }
-
/* If MSb is 1, ASN.1 requires that we prepend a 0. */
if (*p & 0x80) {
if ((p - der_buf_start) < 1) {
diff --git a/tests/suites/test_suite_psa_crypto_util.data b/tests/suites/test_suite_psa_crypto_util.data
index c92b5fc..606e563 100644
--- a/tests/suites/test_suite_psa_crypto_util.data
+++ b/tests/suites/test_suite_psa_crypto_util.data
@@ -115,3 +115,7 @@
ECDSA Raw -> DER, 521bit, Incremental DER buffer sizes
depends_on:PSA_WANT_ECC_SECP_R1_521
ecdsa_raw_to_der_incremental:528:"911111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222":"3081890243009111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111110242222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222"
+
+ECDSA Raw -> DER, 256bit, DER buffer of minimal length (1 byte per integer)
+depends_on:PSA_WANT_ECC_SECP_K1_256
+ecdsa_raw_to_der_incremental:256:"00000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000000000000000000000000000000000002":"3006020101020102"
diff --git a/tests/suites/test_suite_psa_crypto_util.function b/tests/suites/test_suite_psa_crypto_util.function
index c102b07..51f42a7 100644
--- a/tests/suites/test_suite_psa_crypto_util.function
+++ b/tests/suites/test_suite_psa_crypto_util.function
@@ -32,6 +32,7 @@
size_t ret_len;
size_t i;
+ /* Test with an output buffer smaller than required (expexted to fail). */
for (i = 1; i < tmp_buf_len; i++) {
TEST_CALLOC(tmp_buf, i);
TEST_ASSERT(mbedtls_ecdsa_raw_to_der(key_bits, input->x, input->len,
@@ -39,10 +40,16 @@
mbedtls_free(tmp_buf);
tmp_buf = NULL;
}
+ /* Test with an output buffer larger/equal than required (expexted to
+ * succeed). */
+ for (i = tmp_buf_len; i < (2 * tmp_buf_len); i++) {
+ TEST_CALLOC(tmp_buf, i);
+ TEST_ASSERT(mbedtls_ecdsa_raw_to_der(key_bits, input->x, input->len,
+ tmp_buf, i, &ret_len) == 0);
+ mbedtls_free(tmp_buf);
+ tmp_buf = NULL;
+ }
- TEST_CALLOC(tmp_buf, i);
- TEST_EQUAL(mbedtls_ecdsa_raw_to_der(key_bits, input->x, input->len,
- tmp_buf, i, &ret_len), 0);
exit:
mbedtls_free(tmp_buf);
}