add default value for CTR DRBG key size
diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index 70820be..a79dff8 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -2018,7 +2018,7 @@
/**
* \def MBEDTLS_CTR_DRBG_C
*
- * Enable the CTR_DRBG AES-256-based random generator.
+ * Enable the CTR_DRBG AES-256-based(default) or AES-128-based random generator.
*
* Module: library/ctr_drbg.c
* Caller:
@@ -2030,6 +2030,16 @@
#define MBEDTLS_CTR_DRBG_C
/**
+ * configure key size for ctr DRBG , either
+ * MBEDTLS_CTR_DRBG_KEYSIZE_256 (default)
+ * or
+ * MBEDTLS_CTR_DRBG_KEYSIZE_128
+ * must be set.
+ */
+#if !defined(MBEDTLS_CTR_DRBG_KEY_SIZE_128)
+#define MBEDTLS_CTR_DRBG_KEY_SIZE_256 1
+#endif
+/**
* \def MBEDTLS_DEBUG_C
*
* Enable the debug functions.