psa_util: improve leading zeros check in convert_der_to_raw_single_int()
Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/library/psa_util.c b/library/psa_util.c
index 970274e..fd119bf 100644
--- a/library/psa_util.c
+++ b/library/psa_util.c
@@ -488,18 +488,21 @@
return ret;
}
- /* It's invalid to have MSb set without a leading 0x00 (leading 0x00 is
- * checked below). */
- if ((*p & 0x80) != 0) {
+ /* It's invalid to have:
+ * - unpadded_len == 0.
+ * - MSb set without a leading 0x00 (leading 0x00 is checked below). */
+ if (((unpadded_len == 0) || (*p & 0x80) != 0)) {
return MBEDTLS_ERR_ASN1_INVALID_DATA;
}
/* Skip possible leading zero */
- if ((unpadded_len > 0) && (*p == 0x00)) {
+ if (*p == 0x00) {
p++;
unpadded_len--;
- /* Only 1 leading zero is allowed, otherwise that's an error. */
- if (*p == 0x00) {
+ /* It is not allowed to have more than 1 leading zero.
+ * Ignore the case in which unpadded_len = 0 because that's a 0 encoded
+ * in ASN.1 format (i.e. 020100). */
+ if ((unpadded_len > 0) && (*p == 0x00)) {
return MBEDTLS_ERR_ASN1_INVALID_DATA;
}
}