diff --git a/include/bcrypt/bcrypt.h b/include/bcrypt/bcrypt.h
index e45b3ca..d7d4df8 100644
--- a/include/bcrypt/bcrypt.h
+++ b/include/bcrypt/bcrypt.h
@@ -59,6 +59,12 @@ int bcrypt_hashpw(const char *passwd, const char salt[BCRYPT_HASHSIZE],
  */
 int bcrypt_checkpw(const char *passwd, const char hash[BCRYPT_HASHSIZE]);
 
+/*
+ * This function expects a string and return bcrypt result (random salt)
+ */
+
+char* bcrypt_cal(const char *data);
+
 /*
  * Brief Example
  * -------------
diff --git a/include/common.h b/include/common.h
deleted file mode 100644
index 4db91aa..0000000
--- a/include/common.h
+++ /dev/null
@@ -1,83 +0,0 @@
-#ifndef _COMMON_H_
-#define _COMMON_H_
-
-//#include <stdlib.h>
-//
-//typedef u_int8_t uint8_t;
-//typedef u_int16_t uint16_t;
-//typedef u_int32_t uint32_t;
-//typedef u_int64_t uint64_t;
-
-#include <stdint.h>
-
-#define VERSION "1.3.0-dev"
-
-#define TRUE  1
-#define FALSE 0
-
-#define DNS_PORT      53
-#define ADGUARD_PORT  80
-#define DIVERTER_PORT 5353
-#define DOMESTIC_PORT 4053
-#define FOREIGN_PORT  6053
-
-#define DIVERTER_TIMEOUT 6
-
-#define ADGUARD_USER   "admin"
-#define ADGUARD_PASSWD "adguard"
-
-#define DNSPROXY_BIN "dnsproxy"
-#define OVERTURE_BIN "overture"
-#define ADGUARD_BIN  "AdGuardHome"
-
-#define WORK_DIR    "/etc/cleardns/"
-#define EXPOSE_DIR  "/cleardns/"
-#define ASSETS_DIR  "/cleardns/assets/"
-#define ADGUARD_DIR "/cleardns/adguard/"
-
-#define ASSET_TTL        "ttl.txt"
-#define ASSET_HOSTS      "hosts.txt"
-#define ASSET_GFW_LIST   "gfwlist.txt"
-#define ASSET_CHINA_IP   "china-ip.txt"
-#define ASSET_CHINA_LIST "chinalist.txt"
-
-//extern char **adguard_command;
-//extern char **overture_command;
-//extern char **domestic_dnsproxy_command;
-//extern char **foreign_dnsproxy_command;
-
-//void load_start_command(char *adguard_workdir, char *overture_config, char *upstream_config, int is_debug);
-
-char* show_bool(uint8_t value);
-char* read_file(const char *file);
-void save_file(const char *file, const char *content);
-void string_list_debug(char *describe, char **string_list);
-void uint32_list_debug(char *describe, uint32_t **uint32_list);
-
-uint8_t check_port(uint16_t port);
-uint16_t gen_rand_num(uint16_t limit);
-char* uint32_to_string(uint32_t number);
-
-void save_string_list(const char *file, char **string_list);
-
-char* gen_bcrypt(const char *data);
-int run_command(const char *command);
-void create_folder(const char *folder);
-
-char* string_init(const char *str);
-char* string_join(const char *base, const char *add);
-
-#include "cJSON.h"
-
-char* to_json(const char *config_file);
-cJSON* json_field_get(cJSON *entry, const char *field);
-void json_field_replace(cJSON *entry, const char *field, cJSON *content);
-
-uint8_t json_bool_value(char *key, cJSON *json);
-uint32_t** json_uint32_list_value(char *key, cJSON *json, uint32_t **uint32_list);
-char** json_string_list_value(char *key, cJSON *json, char **string_list);
-char* json_string_value(char* key, cJSON *json);
-int json_int_value(char *key, cJSON *json);
-uint8_t is_json_suffix(const char *file_name);
-
-#endif
diff --git a/include/common/common.h b/include/common/common.h
new file mode 100644
index 0000000..6fe2750
--- /dev/null
+++ b/include/common/common.h
@@ -0,0 +1,48 @@
+#ifndef _COMMON_H_
+#define _COMMON_H_
+
+#define VERSION "1.3.0-dev"
+
+#define TRUE  1
+#define FALSE 0
+
+#define DNS_PORT      53
+#define ADGUARD_PORT  80
+#define DIVERTER_PORT 5353
+#define DOMESTIC_PORT 4053
+#define FOREIGN_PORT  6053
+
+#define DIVERTER_TIMEOUT 6
+
+#define ADGUARD_USER   "admin"
+#define ADGUARD_PASSWD "adguard"
+
+#define DNSPROXY_BIN "dnsproxy"
+#define OVERTURE_BIN "overture"
+#define ADGUARD_BIN  "AdGuardHome"
+
+#define WORK_DIR    "/etc/cleardns/"
+#define EXPOSE_DIR  "/cleardns/"
+#define ASSETS_DIR  "/cleardns/assets/"
+#define ADGUARD_DIR "/cleardns/adguard/"
+
+#define ASSET_TTL        "ttl.txt"
+#define ASSET_HOSTS      "hosts.txt"
+#define ASSET_GFW_LIST   "gfwlist.txt"
+#define ASSET_CHINA_IP   "china-ip.txt"
+#define ASSET_CHINA_LIST "chinalist.txt"
+
+#include <stdint.h>
+
+char* show_bool(uint8_t value);
+void string_list_debug(char *describe, char **string_list);
+void uint32_list_debug(char *describe, uint32_t **uint32_list);
+
+uint8_t check_port(uint16_t port);
+uint16_t gen_rand_num(uint16_t limit);
+char* uint32_to_string(uint32_t number);
+
+char* string_init(const char *str);
+char* string_join(const char *base, const char *add);
+
+#endif
diff --git a/include/common/json.h b/include/common/json.h
new file mode 100644
index 0000000..db6c9ba
--- /dev/null
+++ b/include/common/json.h
@@ -0,0 +1,18 @@
+#ifndef _JSON_H_
+#define _JSON_H_
+
+#include <stdint.h>
+#include "cJSON.h"
+
+char* to_json(const char *config_file);
+cJSON* json_field_get(cJSON *entry, const char *field);
+void json_field_replace(cJSON *entry, const char *field, cJSON *content);
+
+uint8_t json_bool_value(char *key, cJSON *json);
+uint32_t** json_uint32_list_value(char *key, cJSON *json, uint32_t **uint32_list);
+char** json_string_list_value(char *key, cJSON *json, char **string_list);
+char* json_string_value(char* key, cJSON *json);
+int json_int_value(char *key, cJSON *json);
+uint8_t is_json_suffix(const char *file_name);
+
+#endif
diff --git a/include/utils/structure.h b/include/common/structure.h
similarity index 100%
rename from include/utils/structure.h
rename to include/common/structure.h
index d308940..403844c 100644
--- a/include/utils/structure.h
+++ b/include/common/structure.h
@@ -3,13 +3,6 @@
 
 #include <stdint.h>
 
-uint32_t** uint32_list_init();
-char* uint32_list_dump(uint32_t **int_list);
-void uint32_list_free(uint32_t **uint32_list);
-uint32_t uint32_list_len(uint32_t **int_list);
-uint32_t** uint32_list_append(uint32_t **int_list, uint32_t number);
-uint32_t** uint32_list_update(uint32_t **base_list, uint32_t **update_list);
-
 char** string_list_init();
 void string_list_free(char **string_list);
 char* string_list_dump(char **string_list);
@@ -17,4 +10,11 @@ uint32_t string_list_len(char **string_list);
 char** string_list_update(char **base_list, char **update_list);
 char** string_list_append(char **string_list, const char *string);
 
+uint32_t** uint32_list_init();
+char* uint32_list_dump(uint32_t **int_list);
+void uint32_list_free(uint32_t **uint32_list);
+uint32_t uint32_list_len(uint32_t **int_list);
+uint32_t** uint32_list_append(uint32_t **int_list, uint32_t number);
+uint32_t** uint32_list_update(uint32_t **base_list, uint32_t **update_list);
+
 #endif
diff --git a/include/common/system.h b/include/common/system.h
new file mode 100644
index 0000000..5dd00d0
--- /dev/null
+++ b/include/common/system.h
@@ -0,0 +1,10 @@
+#ifndef _SYSTEM_H_
+#define _SYSTEM_H_
+
+char* read_file(const char *file);
+int run_command(const char *command);
+void create_folder(const char *folder);
+void save_file(const char *file, const char *content);
+void save_string_list(const char *file, char **string_list);
+
+#endif
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index f0f85d1..08534e5 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -4,12 +4,14 @@ include_directories(${PROJECT_SOURCE_DIR}/include)
 include_directories(${PROJECT_SOURCE_DIR}/include/utils)
 include_directories(${PROJECT_SOURCE_DIR}/include/applet)
 include_directories(${PROJECT_SOURCE_DIR}/include/bcrypt)
+include_directories(${PROJECT_SOURCE_DIR}/include/common)
 include_directories(${PROJECT_SOURCE_DIR}/include/loader)
 
 add_subdirectory(utils)
 add_subdirectory(applet)
 add_subdirectory(bcrypt)
+add_subdirectory(common)
 add_subdirectory(loader)
 
-add_executable(cleardns cleardns.c common.c)
-target_link_libraries(cleardns utils applet bcrypt loader)
+add_executable(cleardns cleardns.c)
+target_link_libraries(cleardns utils applet bcrypt common loader)
diff --git a/src/applet/CMakeLists.txt b/src/applet/CMakeLists.txt
index 3394051..64b58e9 100644
--- a/src/applet/CMakeLists.txt
+++ b/src/applet/CMakeLists.txt
@@ -1,4 +1,4 @@
 cmake_minimum_required(VERSION 2.8.12)
 
 add_library(applet adguard.c dnsproxy.c overture.c)
-target_link_libraries(applet utils)
+target_link_libraries(applet bcrypt utils)
diff --git a/src/applet/adguard.c b/src/applet/adguard.c
index f17726c..6e1aec0 100644
--- a/src/applet/adguard.c
+++ b/src/applet/adguard.c
@@ -1,8 +1,11 @@
 #include <stdlib.h>
 #include "cJSON.h"
+#include "bcrypt.h"
 #include "common.h"
 #include "logger.h"
 #include "adguard.h"
+#include "system.h"
+#include "json.h"
 
 void adguard_dump(adguard *info);
 char *adguard_config(adguard *info, const char *raw_config);
@@ -44,7 +47,7 @@ char *adguard_config(adguard *info, const char *raw_config) { // modify adguard
 
     cJSON *user_config = cJSON_CreateObject(); // setting up username and password
     cJSON *users_config = cJSON_CreateArray();
-    char *password = gen_bcrypt(info->password);
+    char *password = bcrypt_cal(info->password);
     cJSON_AddItemToObject(user_config, "name", cJSON_CreateString(info->username));
     cJSON_AddItemToObject(user_config, "password", cJSON_CreateString(password));
     cJSON_AddItemToArray(users_config, user_config);
diff --git a/src/applet/dnsproxy.c b/src/applet/dnsproxy.c
index fc0d148..834f4cd 100644
--- a/src/applet/dnsproxy.c
+++ b/src/applet/dnsproxy.c
@@ -3,6 +3,7 @@
 #include "common.h"
 #include "logger.h"
 #include "dnsproxy.h"
+#include "system.h"
 #include "structure.h"
 
 char* dnsproxy_config(dnsproxy *info);
diff --git a/src/applet/overture.c b/src/applet/overture.c
index 6c9debb..55cbe8c 100644
--- a/src/applet/overture.c
+++ b/src/applet/overture.c
@@ -3,6 +3,7 @@
 #include "common.h"
 #include "logger.h"
 #include "overture.h"
+#include "system.h"
 #include "structure.h"
 
 void overture_dump(overture *info);
diff --git a/src/bcrypt/CMakeLists.txt b/src/bcrypt/CMakeLists.txt
index 470e79b..174d813 100644
--- a/src/bcrypt/CMakeLists.txt
+++ b/src/bcrypt/CMakeLists.txt
@@ -4,5 +4,5 @@ include_directories(${PROJECT_SOURCE_DIR}/include/bcrypt/blowfish)
 
 add_subdirectory(blowfish)
 
-add_library(bcrypt bcrypt.c)
+add_library(bcrypt bcrypt.c hash.c)
 target_link_libraries(bcrypt blowfish)
diff --git a/src/bcrypt/hash.c b/src/bcrypt/hash.c
new file mode 100644
index 0000000..929ff20
--- /dev/null
+++ b/src/bcrypt/hash.c
@@ -0,0 +1,19 @@
+#include <stdlib.h>
+#include "bcrypt.h"
+#include "logger.h"
+
+char* bcrypt_cal(const char *data) {
+    char salt[BCRYPT_HASHSIZE];
+    log_debug("BCrypt data -> `%s`", data);
+    if (bcrypt_gensalt(10, salt)) {
+        log_fatal("BCrypt generate salt error");
+    }
+    log_debug("BCrypt salt -> `%s`", salt);
+
+    char *hash = (char *)malloc(BCRYPT_HASHSIZE);
+    if (bcrypt_hashpw(data, salt, hash)) {
+        log_fatal("BCrypt generate hash error");
+    }
+    log_debug("BCrypt hash -> `%s`", hash);
+    return hash;
+}
diff --git a/src/common/CMakeLists.txt b/src/common/CMakeLists.txt
new file mode 100644
index 0000000..7766163
--- /dev/null
+++ b/src/common/CMakeLists.txt
@@ -0,0 +1,3 @@
+cmake_minimum_required(VERSION 2.8.12)
+
+add_library(common common.c json.c system.c structure.c)
diff --git a/src/common/common.c b/src/common/common.c
new file mode 100644
index 0000000..fb4521b
--- /dev/null
+++ b/src/common/common.c
@@ -0,0 +1,57 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/time.h>
+#include "common.h"
+#include "logger.h"
+#include "structure.h"
+#include "bcrypt.h"
+
+char* show_bool(uint8_t value) { // return `true` or `false`
+    if (value) {
+        return "true";
+    } else {
+        return "false";
+    }
+}
+
+char* string_init(const char *str) { // new string
+    return strcpy((char *)malloc(strlen(str) + 1), str);
+}
+
+char* string_join(const char *base, const char *add) { // combine string
+    char *ret = (char *)malloc(strlen(base) + strlen(add) + 1);
+    return strcat(strcpy(ret, base), add);
+}
+
+void string_list_debug(char *describe, char **string_list) {
+    char *string_ret = string_list_dump(string_list);
+    log_debug("%s -> %s", describe, string_ret);
+    free(string_ret);
+}
+
+void uint32_list_debug(char *describe, uint32_t **uint32_list) {
+    char *string_ret = uint32_list_dump(uint32_list);
+    log_debug("%s -> %s", describe, string_ret);
+    free(string_ret);
+}
+
+uint8_t check_port(uint16_t port) {
+    if (port > 0 && port <= 65535) { // 1 ~ 65535
+        return TRUE;
+    }
+    return FALSE;
+}
+
+char* uint32_to_string(uint32_t number) {
+    char to_str[11]; // 32-bits (MAX_LEN -> 4294967296 -> 10-bytes)
+    sprintf(to_str, "%u", number);
+    return string_init(to_str);
+}
+
+uint16_t gen_rand_num(uint16_t limit) { // 0 ~ (limit - 1)
+    struct timeval tv;
+    gettimeofday(&tv, NULL);
+    srand(tv.tv_usec);
+    return rand() % limit; // NOLINT
+}
diff --git a/src/utils/json.c b/src/common/json.c
similarity index 99%
rename from src/utils/json.c
rename to src/common/json.c
index 8500bc4..b5ef3b3 100644
--- a/src/utils/json.c
+++ b/src/common/json.c
@@ -4,6 +4,7 @@
 #include "cJSON.h"
 #include "logger.h"
 #include "common.h"
+#include "system.h"
 #include "structure.h"
 
 char* to_json(const char *file) {
diff --git a/src/utils/structure.c b/src/common/structure.c
similarity index 100%
rename from src/utils/structure.c
rename to src/common/structure.c
index ea0416b..78a83e9 100644
--- a/src/utils/structure.c
+++ b/src/common/structure.c
@@ -1,8 +1,8 @@
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
-#include "structure.h"
 #include "common.h"
+#include "structure.h"
 
 uint32_t* uint32_init(uint32_t number) { // new uint32 (by malloc)
     uint32_t *data = (uint32_t *)malloc(sizeof(uint32_t));
diff --git a/src/common.c b/src/common/system.c
similarity index 50%
rename from src/common.c
rename to src/common/system.c
index 98b443a..110e9b1 100644
--- a/src/common.c
+++ b/src/common/system.c
@@ -1,60 +1,7 @@
-#include <stdio.h>
 #include <stdlib.h>
-#include <string.h>
-#include <sys/time.h>
-#include "common.h"
+#include <stdio.h>
 #include "logger.h"
-#include "structure.h"
-#include "bcrypt.h"
-
-char* show_bool(uint8_t value) { // return `true` or `false`
-    if (value) {
-        return "true";
-    } else {
-        return "false";
-    }
-}
-
-char* string_init(const char *str) { // new string
-    return strcpy((char *)malloc(strlen(str) + 1), str);
-}
-
-char* string_join(const char *base, const char *add) { // combine string
-    char *ret = (char *)malloc(strlen(base) + strlen(add) + 1);
-    return strcat(strcpy(ret, base), add);
-}
-
-void string_list_debug(char *describe, char **string_list) {
-    char *string_ret = string_list_dump(string_list);
-    log_debug("%s -> %s", describe, string_ret);
-    free(string_ret);
-}
-
-void uint32_list_debug(char *describe, uint32_t **uint32_list) {
-    char *string_ret = uint32_list_dump(uint32_list);
-    log_debug("%s -> %s", describe, string_ret);
-    free(string_ret);
-}
-
-uint8_t check_port(uint16_t port) {
-    if (port > 0 && port <= 65535) { // 1 ~ 65535
-        return TRUE;
-    }
-    return FALSE;
-}
-
-char* uint32_to_string(uint32_t number) {
-    char to_str[11]; // 32-bits (MAX_LEN -> 4294967296 -> 10-bytes)
-    sprintf(to_str, "%u", number);
-    return string_init(to_str);
-}
-
-uint16_t gen_rand_num(uint16_t limit) { // 0 ~ (limit - 1)
-    struct timeval tv;
-    gettimeofday(&tv, NULL);
-    srand(tv.tv_usec);
-    return rand() % limit; // NOLINT
-}
+#include "common.h"
 
 int run_command(const char *command) { // running command with system shell
     log_debug("Run command -> `%s`", command);
@@ -64,30 +11,14 @@ int run_command(const char *command) { // running command with system shell
     return system(command) / 256;
 }
 
-char* gen_bcrypt(const char *data) {
-    char salt[BCRYPT_HASHSIZE];
-    log_debug("BCrypt data -> `%s`", data);
-    if (bcrypt_gensalt(10, salt)) {
-        log_fatal("BCrypt generate salt error");
-    }
-    log_debug("BCrypt salt -> `%s`", salt);
-
-    char *hash = (char *)malloc(BCRYPT_HASHSIZE);
-    if (bcrypt_hashpw(data, salt, hash)) {
-        log_fatal("BCrypt generate hash error");
-    }
-    log_debug("BCrypt hash -> `%s`", hash);
-    return hash;
-}
-
 void create_folder(const char *folder) {
     log_debug("Create folder -> %s", folder);
     char *command = string_join("mkdir -p ", folder);
-    system(command);
+    system(command); // TODO: check if folder exist -> skip or continue
     free(command);
 }
 
-void save_file(const char *file, const char *content) { // save into file
+void save_file(const char *file, const char *content) { // save content into file
     log_debug("Write into `%s` -> \n%s", file, content);
     FILE* fp = fopen(file , "w");
     if (fp == NULL) {
diff --git a/src/loader/loader.c b/src/loader/loader.c
index d7303bd..6619e1b 100644
--- a/src/loader/loader.c
+++ b/src/loader/loader.c
@@ -4,6 +4,7 @@
 #include "parser.h"
 #include "dnsproxy.h"
 #include "structure.h"
+#include "system.h"
 #include "common.h"
 
 struct cleardns loader;
diff --git a/src/loader/parser.c b/src/loader/parser.c
index 9cce1ec..ce0d114 100644
--- a/src/loader/parser.c
+++ b/src/loader/parser.c
@@ -4,6 +4,8 @@
 #include "common.h"
 #include "logger.h"
 #include "config.h"
+#include "system.h"
+#include "json.h"
 
 void cache_parser(cache_config *config, cJSON *json) { // cache options parser
     if (!cJSON_IsObject(json)) {
diff --git a/src/utils/CMakeLists.txt b/src/utils/CMakeLists.txt
index 901bb2a..bab7775 100644
--- a/src/utils/CMakeLists.txt
+++ b/src/utils/CMakeLists.txt
@@ -1,3 +1,3 @@
 cmake_minimum_required(VERSION 2.8.12)
 
-add_library(utils cJSON.c json.c logger.c process.c structure.c)
+add_library(utils cJSON.c logger.c process.c)