diff --git a/dependencies/tlibc b/dependencies/tlibc
index 1775b27..adaf5cc 160000
--- a/dependencies/tlibc
+++ b/dependencies/tlibc
@@ -1 +1 @@
-Subproject commit 1775b27980d550dd9a50a81b11d797c51253ab22
+Subproject commit adaf5cc31199b8b70404f30b51a0e4ef822d6fab
diff --git a/src/common_constants.h b/src/common_constants.h
new file mode 100644
index 0000000..7095110
--- /dev/null
+++ b/src/common_constants.h
@@ -0,0 +1,11 @@
+#pragma once
+#include "tlibc/std.h"
+
+#define USERNAME_SIZE_MIN 2
+#define USERNAME_SIZE_MAX 63
+#define PASSWORD_SIZE_MIN 8
+#define PASSWORD_SIZE_MAX 31
+#define PASSWORD_HASH_SIZE 32
+#define CHANNEL_NAME_MIN 1
+#define CHANNEL_NAME_MAX 127
+#define CHANNEL_DESC_MAX 4095
diff --git a/src/cryptography/cryptography.h b/src/cryptography/cryptography.h
index 468febc..2623377 100755
--- a/src/cryptography/cryptography.h
+++ b/src/cryptography/cryptography.h
@@ -2,6 +2,7 @@
 #include "tlibc/collections/Array.h"
 #include "tlibc/errors.h"
 #include "bearssl_rand.h"
+#include "common_constants.h"
 
 //////////////////////////////////////////////////////////////////////////////
 //                                                                          //
@@ -14,7 +15,6 @@
 /// @param out_buffer u8[PASSWORD_HASH_SIZE]
 /// @param rounds number of rounds
 void hash_password(Array(u8) password, u8* out_buffer, i32 rounds);
-#define PASSWORD_HASH_SIZE 32
 #define PASSWORD_HASH_LVL_ROUNDS 1e5
 
 //////////////////////////////////////////////////////////////////////////////
diff --git a/src/db/idb.h b/src/db/idb.h
index 9da7b23..017a9bc 100644
--- a/src/db/idb.h
+++ b/src/db/idb.h
@@ -14,13 +14,13 @@ void idb_close(IncrementalDB* db);
 
 Result(Table*) idb_getOrCreateTable(IncrementalDB* db, str table_name, u32 row_size);
 
-Result(void) idb_getRows(Table* t, u64 id, void* dst, u64 count);
+Result(void) idb_getRows(Table* t, u64 start_from_id, void* dst, u64 count);
 #define idb_getRow(T, ID, DST) idb_getRows(T, ID, DST, 1)
 
 Result(u64) idb_pushRows(Table* t, const void* src, u64 count);
 #define idb_pushRow(T, SRC) idb_pushRows(T, SRC, 1)
 
-Result(void) idb_updateRows(Table* t, u64 id, const void* src, u64 count);
+Result(void) idb_updateRows(Table* t, u64 start_from_id, const void* src, u64 count);
 #define idb_updateRow(T, ID, SRC) idb_updateRows(T, ID, SRC, 1)
 
 Result(u64) idb_getRowCount(Table* t);
diff --git a/src/network/tcp-chat-protocol/constant.h b/src/network/tcp-chat-protocol/constant.h
index 45edcc3..a67448a 100644
--- a/src/network/tcp-chat-protocol/constant.h
+++ b/src/network/tcp-chat-protocol/constant.h
@@ -1,6 +1,7 @@
 #pragma once
 #include "tlibc/errors.h"
 #include "magic.h"
+#include "common_constants.h"
 
 #define AES_SESSION_KEY_SIZE 32
 
diff --git a/src/network/tcp-chat-protocol/v1.c b/src/network/tcp-chat-protocol/v1.c
index a956538..3776970 100644
--- a/src/network/tcp-chat-protocol/v1.c
+++ b/src/network/tcp-chat-protocol/v1.c
@@ -56,8 +56,8 @@ Result(void) RegisterRequest_tryConstruct(RegisterRequest *ptr, PacketHeader* he
     _PacketHeader_construct(RegisterRequest);
 
     try_assert(username.size >= USERNAME_SIZE_MIN && username.size <= USERNAME_SIZE_MAX);
-    ptr->username_size = username.size;
     memcpy(ptr->username, username.data, username.size);
+    ptr->username[username.size] = 0;
 
     try_assert(token.size == sizeof(ptr->token));
     memcpy(ptr->token, token.data, token.size);
diff --git a/src/network/tcp-chat-protocol/v1.h b/src/network/tcp-chat-protocol/v1.h
index 17f508b..0b223bf 100644
--- a/src/network/tcp-chat-protocol/v1.h
+++ b/src/network/tcp-chat-protocol/v1.h
@@ -2,7 +2,6 @@
 #include "tlibc/errors.h"
 #include "tlibc/string/str.h"
 #include "network/tcp-chat-protocol/constant.h"
-#include "cryptography/cryptography.h"
 
 #define PROTOCOL_VERSION 1 /* 1.0.0 */
 #define NETWORK_BUFFER_SIZE 65536
@@ -80,14 +79,8 @@ void LoginResponse_construct(LoginResponse* ptr, PacketHeader* header,
     u64 user_id, u64 landing_channel_id);
 
 
-#define USERNAME_SIZE_MIN 4
-#define USERNAME_SIZE_MAX 64
-#define PASSWORD_SIZE_MIN 8
-#define PASSWORD_SIZE_MAX 32
-
 typedef struct RegisterRequest {
-    u32 username_size;
-    char username[USERNAME_SIZE_MAX];
+    char username[USERNAME_SIZE_MAX + 1]; // null-terminated
     u8 token[PASSWORD_HASH_SIZE];
 } ALIGN_PACKET_STRUCT RegisterRequest;
 
diff --git a/src/server/db_tables.h b/src/server/db_tables.h
new file mode 100644
index 0000000..6833893
--- /dev/null
+++ b/src/server/db_tables.h
@@ -0,0 +1,17 @@
+#pragma once
+#include "common_constants.h"
+#include "tlibc/time.h"
+
+typedef struct User {
+    u16 name_len;
+    char name[USERNAME_SIZE_MAX + 1];  // null-terminated
+    u8 token_hash[PASSWORD_HASH_SIZE]; // token is hashed again on server side
+    DateTime registration_time;
+} ATTRIBUTE_ALIGNED(256) User;
+
+typedef struct Channel {
+    u16 name_len;
+    u16 desc_len;
+    char name[CHANNEL_NAME_MAX + 1];
+    char desc[CHANNEL_DESC_MAX + 1];
+} ATTRIBUTE_ALIGNED(16*1024) Channel;
diff --git a/src/server/request_handlers/Register.c b/src/server/request_handlers/Register.c
index a18c9eb..bc955c5 100644
--- a/src/server/request_handlers/Register.c
+++ b/src/server/request_handlers/Register.c
@@ -9,8 +9,62 @@ declare_RequestHandler(Register)
     try_void(PacketHeader_validateContentSize(req_head, sizeof(req)));
     try_void(EncryptedSocketTCP_recvStruct(&conn->sock, &req));
 
-    //TODO: try register client
-    u64 user_id;
+    //TODO: reject usernames with restricted characters
+    // must end with 0
+    if(req.username[sizeof(req.username - 1)] != 0){
+        try(char* err_msg, p, sendErrorMessage(conn, res_head, 
+            "Username is incorrect\n"));
+        logWarn(log_ctx, "%s", err_msg);
+        free(err_msg);
+        Return RESULT_VOID;
+    }
+    // check username size
+    str username_str = str_from_cstr(req.username);
+    if(username_str.size < USERNAME_SIZE_MIN){
+        try(char* err_msg, p, sendErrorMessage(conn, res_head, 
+            "Username length (in bytes) must be >= %i and <= %i\n", 
+            USERNAME_SIZE_MIN, USERNAME_SIZE_MAX));
+        logWarn(log_ctx, "%s", err_msg);
+        free(err_msg);
+        Return RESULT_VOID;
+    }
+
+    // lock users cache
+    try_stderrcode(pthread_mutex_lock(&server->users_cache_mutex));
+    bool unlocked_users_cache_mutex = false;
+    Defer(if(!unlocked_users_cache_mutex) pthread_mutex_unlock(&server->users_cache_mutex));
+
+    // check if name is taken
+    if(HashMap_tryGetPtr(&server->users_name_id_map, username_str) != NULL){
+        try(char* err_msg, p, sendErrorMessage(conn, res_head, 
+            "User with name '%s' already exists\n", 
+            username_str.data));
+        logWarn(log_ctx, "%s", err_msg);
+        free(err_msg);
+        Return RESULT_VOID;
+    }
+
+    // initialize new user
+    User user;
+    memset(&user, 0, sizeof(User));
+    memcpy(user.name, username_str.data, username_str.size + 1);
+    user.name_len = username_str.size;
+    hash_password(
+        Array_construct_size(req.token, sizeof(req.token)), 
+        user.token_hash,
+        PASSWORD_HASH_LVL_ROUNDS
+    );
+    DateTime_getUTC(&user.registration_time);
+    
+    // save new user to db and cache
+    try(u64 user_id, u, idb_pushRow(server->db_users_table, &user));
+    try_assert(List_len(server->users_cache_list, User) == user_id);
+    List_push(&server->users_cache_list, User, user);
+    try_assert(HashMap_tryPush(&server->users_name_id_map, username_str, &user_id));
+    
+    // manually unlock mutex
+    pthread_mutex_unlock(&server->users_cache_mutex);
+    unlocked_users_cache_mutex = true;
 
     RegisterResponse res = {0};
     RegisterResponse_construct(&res, res_head, user_id);
diff --git a/src/server/request_handlers/ServerPublicInfo.c b/src/server/request_handlers/ServerPublicInfo.c
index d36061f..e1485d2 100644
--- a/src/server/request_handlers/ServerPublicInfo.c
+++ b/src/server/request_handlers/ServerPublicInfo.c
@@ -12,12 +12,14 @@ declare_RequestHandler(ServerPublicInfo)
     //TODO: try find requested info
     Array(u8) content;
     switch(req.property){
-        default:
+        default:{
             try(char* err_msg, p, sendErrorMessage(conn, res_head, 
-                "unknown ServerPublicInfo property %u", req.property));
+                "Unknown ServerPublicInfo property %u",
+                req.property));
             logWarn(log_ctx, "%s", err_msg);
+            free(err_msg);
             Return RESULT_VOID;
-            break;
+        }
         case ServerPublicInfo_Name:
             content = str_castTo_Array(server->name);
             break;
diff --git a/src/server/server.c b/src/server/server.c
index 55973f1..e78c358 100644
--- a/src/server/server.c
+++ b/src/server/server.c
@@ -18,6 +18,9 @@ void Server_free(Server* server){
     free(server->description.data);
     ServerCredentials_destroy(&server->cred);
     idb_close(server->db);
+    pthread_mutex_destroy(&server->users_cache_mutex);
+    free(server->users_cache_list.data);
+    HashMap_destroy(&server->users_name_id_map);
 }
 
 Result(Server*) Server_createFromConfig(cstr config_path){
@@ -76,6 +79,23 @@ Result(Server*) Server_createFromConfig(cstr config_path){
     try_void(config_findValue(config_str, STR("db_dir"), &tmp_str, true));
     try(server->db, p, idb_open(tmp_str, db_aes_key));
 
+    // build users cache
+    pthread_mutex_init(&server->users_cache_mutex, NULL);
+    try(server->db_users_table, p, idb_getOrCreateTable(server->db, STR("users"), sizeof(User)));
+    try(u64 users_count, u, idb_getRowCount(server->db_users_table));
+    server->users_cache_list = List_alloc(User, users_count);
+    HashMap_construct(&server->users_name_id_map, u64, NULL);
+    // load whole table to list
+    try_void(idb_getRows(server->db_users_table, 0, server->users_cache_list.data, users_count));
+    // build name-id map
+    for(u64 id; id < users_count; id++){
+        User* u = &List_index(server->users_cache_list, User, id);
+        str key = str_construct(u->name, u->name_len, true);
+        if(!HashMap_tryPush(&server->users_name_id_map, key, &id)){
+            Return RESULT_ERROR_FMT("duplicate user name '%s'", u->name);
+        }
+    }
+
     success = true;
     Return RESULT_VALUE(p, server);
 }
@@ -154,10 +174,9 @@ static Result(void) try_handleConnection(ConnectionHandlerArgs* args, cstr log_c
                 try(char* err_msg, p,
                     sendErrorMessage(conn, &res_head,
                         "Received unexpected packet of type %u",
-                        req_head.type
-                    )
-                );
+                        req_head.type));
                 logWarn(log_ctx, "%s", err_msg);
+                free(err_msg);
                 Return RESULT_VOID;
             
             // unauthorized requests
diff --git a/src/server/server.h b/src/server/server.h
index 2de6a9c..a03d54c 100644
--- a/src/server/server.h
+++ b/src/server/server.h
@@ -3,6 +3,10 @@
 #include "cryptography/RSA.h"
 #include "network/encrypted_sockets.h"
 #include "db/idb.h"
+#include "tlibc/collections/HashMap.h"
+#include "tlibc/collections/List.h"
+#include "db_tables.h"
+#include <pthread.h>
 
 typedef struct Server Server;
 
@@ -44,6 +48,10 @@ typedef struct Server {
     EndpointIPv4 local_end;
     ServerCredentials cred;
     IncrementalDB* db;
+    Table* db_users_table;
+    pthread_mutex_t users_cache_mutex;
+    List(User) users_cache_list; // index is id
+    HashMap(u64) users_name_id_map; //key is user name
 } Server;
 
 Result(Server*) Server_createFromConfig(cstr config_path);