Add special return code for ecdsa length mismatch
diff --git a/include/polarssl/ecdsa.h b/include/polarssl/ecdsa.h
index b5e363e..4f06328 100644
--- a/include/polarssl/ecdsa.h
+++ b/include/polarssl/ecdsa.h
@@ -175,7 +175,9 @@
* \param slen Size of sig
*
* \return 0 if successful,
- * POLARSSL_ERR_ECP_BAD_INPUT_DATA if signature is invalid
+ * POLARSSL_ERR_ECP_BAD_INPUT_DATA if signature is invalid,
+ * POLARSSL_ERR_ECP_SIG_LEN_MISTMATCH if the signature is
+ * valid but its actual length is less than siglen,
* or a POLARSSL_ERR_ECP or POLARSSL_ERR_MPI error code
*/
int ecdsa_read_signature( ecdsa_context *ctx,