rsa.c: provide interface to get padding mode of RSA context

Signed-off-by: Yanray Wang <yanray.wang@arm.com>

include/mbedtls/rsa.h

@@ -181,6 +181,16 @@ void mbedtls_rsa_init(mbedtls_rsa_context *ctx);
 int mbedtls_rsa_set_padding(mbedtls_rsa_context *ctx, int padding,
                             mbedtls_md_type_t hash_id);
 
+/**
+ * \brief          This function retrieves padding mode of RSA modulus.
+ *
+ * \param ctx      The initialized RSA context.
+ *
+ * \return         RSA padding mode.
+ *
+ */
+int mbedtls_rsa_get_padding_mode(const mbedtls_rsa_context *ctx);
+
 /**
  * \brief          This function imports a set of core parameters into an
  *                 RSA context.

library/rsa.c

@@ -499,10 +499,17 @@ int mbedtls_rsa_set_padding(mbedtls_rsa_context *ctx, int padding,
     return 0;
 }
 
+/*
+ * Get padding mode of RSA modulus
+ */
+int mbedtls_rsa_get_padding_mode(const mbedtls_rsa_context *ctx)
+{
+    return ctx->MBEDTLS_PRIVATE(padding);
+}
+
 /*
  * Get length in bytes of RSA modulus
  */
-
 size_t mbedtls_rsa_get_len(const mbedtls_rsa_context *ctx)
 {
     return ctx->len;