Store proper name with version in fork file (#95)

* Store proper name with version in fork file

Currently the fork file stores just the string "master-key", which is incorrect,
as it does not contain the version information. To counteract this, at read time
it loads the latest master key, but that can be different than the version which
was used to encrypt it.

These getLatestKey calls also lead to postgres making many unneccessary calls to
vault, making this bug partially responsible for #90.

The fix is simple, from now on we correctly write the entire string including the
version number, and read the specified version at read time.

Fixes #94.

* fixing review comment

src/access/pg_tde_tdemap.c

@@ -124,7 +124,7 @@ pg_tde_write_key_fork(const RelFileLocator *rlocator, InternalKey *key, const ch
 	 * the cache as well */
 	data = (RelKeysData *) MemoryContextAlloc(TopMemoryContext, SizeOfRelKeysData(1));
 
-	strcpy(data->master_key_name, MasterKeyName);
+	strncpy(data->master_key_name, master_key_info->name.name, MASTER_KEY_NAME_LEN);
 	data->internal_key[0] = *key;
 	data->internal_keys_len = 1;
 
@@ -217,11 +217,9 @@ pg_tde_get_keys_from_fork(const RelFileLocator *rlocator)
 		// TODO: use proper iv stored in the file!
 		unsigned char iv[INTERNAL_KEY_LEN] = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };
 
-		master_key_info = keyringGetLatestKey(keys->master_key_name);
-		if(master_key_info == NULL)
-		{
-			master_key_info = keyringGenerateKey(keys->master_key_name, INTERNAL_KEY_LEN);
-		}
+		keyName master_key_name;
+		strncpy(master_key_name.name, keys->master_key_name, MASTER_KEY_NAME_LEN);
+		master_key_info = keyringGetKey(master_key_name);
 		if(master_key_info == NULL)
 		{
 			ereport(ERROR,
@@ -414,4 +412,4 @@ pg_tde_xlog_create_fork(XLogReaderState *record)
 #endif
 
 	pg_tde_write_key_fork(&rlocator, &int_key, MasterKeyName);	
-}
+}