Document AES functions and fix free() functions
diff --git a/include/mbedtls/aes.h b/include/mbedtls/aes.h
index cfb20c4..da7ab54 100644
--- a/include/mbedtls/aes.h
+++ b/include/mbedtls/aes.h
@@ -121,14 +121,14 @@
* It must be the first API called before using
* the context.
*
- * \param ctx The AES context to initialize.
+ * \param ctx The AES context to initialize. Must not be NULL.
*/
void mbedtls_aes_init( mbedtls_aes_context *ctx );
/**
* \brief This function releases and clears the specified AES context.
*
- * \param ctx The AES context to clear.
+ * \param ctx The AES context to clear. If NULL, no action is taken.
*/
void mbedtls_aes_free( mbedtls_aes_context *ctx );
@@ -139,14 +139,14 @@
* It must be the first API called before using
* the context.
*
- * \param ctx The AES XTS context to initialize.
+ * \param ctx The AES XTS context to initialize. Must not be NULL.
*/
void mbedtls_aes_xts_init( mbedtls_aes_xts_context *ctx );
/**
* \brief This function releases and clears the specified AES XTS context.
*
- * \param ctx The AES XTS context to clear.
+ * \param ctx The AES XTS context to clear. If NULL, no action is taken.
*/
void mbedtls_aes_xts_free( mbedtls_aes_xts_context *ctx );
#endif /* MBEDTLS_CIPHER_MODE_XTS */
@@ -154,8 +154,9 @@
/**
* \brief This function sets the encryption key.
*
- * \param ctx The AES context to which the key should be bound.
- * \param key The encryption key.
+ * \param ctx The AES context to which the key should be bound. Must not
+ * be NULL.
+ * \param key The encryption key. Must not be NULL.
* \param keybits The size of data passed in bits. Valid options are:
* <ul><li>128 bits</li>
* <li>192 bits</li>
@@ -170,8 +171,9 @@
/**
* \brief This function sets the decryption key.
*
- * \param ctx The AES context to which the key should be bound.
- * \param key The decryption key.
+ * \param ctx The AES context to which the key should be bound. Must not
+ * be NULL.
+ * \param key The decryption key. Must not be NULL.
* \param keybits The size of data passed. Valid options are:
* <ul><li>128 bits</li>
* <li>192 bits</li>