diff --git a/UC/backend/src/app.js b/UC/backend/src/app.js
index 47f9b42..0b7849a 100644
--- a/UC/backend/src/app.js
+++ b/UC/backend/src/app.js
@@ -10,6 +10,9 @@ app.use(cors({
 }));
 app.use(json());
 
+const {apiKey} = require('./config.json');
+app.locals.apiKey = apiKey;
+
 const {
     usersDB,
     departmentsDB,
diff --git a/UC/backend/src/config.json b/UC/backend/src/config.json
new file mode 100644
index 0000000..ba0ff54
--- /dev/null
+++ b/UC/backend/src/config.json
@@ -0,0 +1,3 @@
+{
+  "apiKey": "uc_api"
+}
\ No newline at end of file
diff --git a/UC/backend/src/db/jsonDatabaseManager.js b/UC/backend/src/db/jsonDatabaseManager.js
index ca524b1..f96d424 100644
--- a/UC/backend/src/db/jsonDatabaseManager.js
+++ b/UC/backend/src/db/jsonDatabaseManager.js
@@ -31,6 +31,48 @@ class JSONDatabase {
             console.error('Error writing file:', error);
         }
     }
+
+    isKeyValue(key, value) {
+        const data = this.readFile();
+        if (!data) {
+            return false;
+        }
+
+        for (const item of data) {
+            if (item[key] === value) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    findIndexByKeyValueInArray(key, value) {
+        const data = this.readFile();
+        if (!data || !Array.isArray(data)) {
+            return -1;
+        }
+
+        for (let i = 0; i < data.length; i++) {
+            if (data[i][key] === value) {
+                return i;
+            }
+        }
+        return -1;
+    }
+
+    findByKeyValue(key, value) {
+        const data = this.readFile();
+        if (!data || !Array.isArray(data)) {
+            return null; // Database read failed or data is not an array
+        }
+
+        for (const item of data) {
+            if (item[key] === value) {
+                return item; // Return the object containing the specified key-value pair
+            }
+        }
+        return null; // No matching key-value pair found
+    }
 }
 
 const usersDB = new JSONDatabase(path.join(__dirname, 'users.json'));
diff --git a/UC/backend/src/models/ceoModifyModel.js b/UC/backend/src/models/ceoModifyModel.js
new file mode 100644
index 0000000..d757447
--- /dev/null
+++ b/UC/backend/src/models/ceoModifyModel.js
@@ -0,0 +1,15 @@
+const Joi = require('joi');
+
+const ceoModifyModel = Joi.object({
+    name: Joi.string().required().messages({
+        'any.required': 'CEO name is required',
+        'string.empty': 'CEO name must not be empty'
+    }),
+    email: Joi.string().email().required().messages({
+        'any.required': 'CEO email is required',
+        'string.empty': 'CEO email must not be empty',
+        'string.email': 'CEO email must be a valid email address'
+    })
+});
+
+module.exports = ceoModifyModel;
\ No newline at end of file
diff --git a/UC/backend/src/models/ceoPasswordModel.js b/UC/backend/src/models/ceoPasswordModel.js
new file mode 100644
index 0000000..9cbd3f1
--- /dev/null
+++ b/UC/backend/src/models/ceoPasswordModel.js
@@ -0,0 +1,10 @@
+const Joi = require('joi');
+
+const ceoPasswordModel = Joi.object({
+    password: Joi.string().required().messages({
+        'any.required': 'Password is required',
+        'string.empty': 'Password must not be empty'
+    })
+});
+
+module.exports = ceoPasswordModel;
\ No newline at end of file
diff --git a/UC/backend/src/models/ceoRegisterModel.js b/UC/backend/src/models/ceoRegisterModel.js
deleted file mode 100644
index 8286e23..0000000
--- a/UC/backend/src/models/ceoRegisterModel.js
+++ /dev/null
@@ -1,8 +0,0 @@
-const Joi = require('joi');
-
-const ceoRegisterModel = Joi.object({
-    name: Joi.string().required(),
-    email: Joi.string().email().required()
-});
-
-module.exports = ceoRegisterModel;
\ No newline at end of file
diff --git a/UC/backend/src/models/departmentRegisterModel.js b/UC/backend/src/models/departmentRegisterModel.js
index 9d4d182..2d45bad 100644
--- a/UC/backend/src/models/departmentRegisterModel.js
+++ b/UC/backend/src/models/departmentRegisterModel.js
@@ -1,7 +1,10 @@
 const Joi = require('joi');
 
 const departmentRegisterModel = Joi.object({
-    name: Joi.string().required()
+    name: Joi.string().required().messages({
+        'any.required': 'Department name is required',
+        'string.empty': 'Department name must not be empty'
+    })
 });
 
 module.exports = departmentRegisterModel
\ No newline at end of file
diff --git a/UC/backend/src/models/dirStructureModel.js b/UC/backend/src/models/dirStructureModel.js
index 5cefb4a..f269bee 100644
--- a/UC/backend/src/models/dirStructureModel.js
+++ b/UC/backend/src/models/dirStructureModel.js
@@ -1,9 +1,20 @@
 const Joi = require('joi');
 
 const dirStructureModel = Joi.object({
-    id: Joi.string().guid().required(),
-    dir_config: Joi.string().required(),
-    total_space: Joi.number().positive().required()
+    id: Joi.string().guid().required().messages({
+        'any.required': 'ID is required',
+        'string.empty': 'ID must not be empty',
+        'string.guid': 'ID must be a valid GUID'
+    }),
+    dir_config: Joi.string().required().messages({
+        'any.required': 'Directory configuration is required',
+        'string.empty': 'Directory configuration must not be empty'
+    }),
+    total_space: Joi.number().positive().required().messages({
+        'any.required': 'Total space is required',
+        'number.positive': 'Total space must be a positive number',
+        'number.base': 'Total space must be a number'
+    })
 });
 
 module.exports = dirStructureModel
\ No newline at end of file
diff --git a/UC/backend/src/models/emailVerificationModel.js b/UC/backend/src/models/emailVerificationModel.js
index d93342f..32ba392 100644
--- a/UC/backend/src/models/emailVerificationModel.js
+++ b/UC/backend/src/models/emailVerificationModel.js
@@ -1,7 +1,11 @@
 const Joi = require('joi');
 
 const emailVerificationModel = Joi.object({
-    email: Joi.string().email().required()
+    email: Joi.string().email().required().messages({
+        'string.empty': 'Email can\'t be empty.',
+        'string.email': 'Invalid email format.',
+        'any.required': 'Email is required'
+    })
 });
 
 module.exports = emailVerificationModel;
\ No newline at end of file
diff --git a/UC/backend/src/models/schemaMapper.js b/UC/backend/src/models/schemaMapper.js
index 06e332f..fb93d43 100644
--- a/UC/backend/src/models/schemaMapper.js
+++ b/UC/backend/src/models/schemaMapper.js
@@ -3,9 +3,10 @@ const usersLoginModelSchema = require('./usersLoginModel');
 const usersModifyModelSchema = require('./usersModifyModel');
 const dirStructureModelSchema = require('./dirStructureModel');
 const departmentRegisterModelSchema = require('./departmentRegisterModel');
-const ceoRegisterModelSchema = require('./ceoRegisterModel');
+const ceoModifyModelSchema = require('./ceoModifyModel');
 const emailVerificationSchema = require('./emailVerificationModel');
 const userDepartmentPatchSchema = require('./userDepartmentPatchModel');
+const ceoPasswordModelSchema = require('./ceoPasswordModel');
 
 module.exports = {
     schemas: {
@@ -14,8 +15,9 @@ module.exports = {
         usersLoginModelSchema,
         usersModifyModelSchema,
         departmentRegisterModelSchema,
-        ceoRegisterModelSchema,
+        ceoModifyModelSchema,
         emailVerificationSchema,
-        userDepartmentPatchSchema
+        userDepartmentPatchSchema,
+        ceoPasswordModelSchema
     },
 };
\ No newline at end of file
diff --git a/UC/backend/src/models/userDepartmentPatchModel.js b/UC/backend/src/models/userDepartmentPatchModel.js
index 75e4992..5dd2c00 100644
--- a/UC/backend/src/models/userDepartmentPatchModel.js
+++ b/UC/backend/src/models/userDepartmentPatchModel.js
@@ -1,7 +1,11 @@
 const Joi = require("joi");
 
 const UserDepartmentPatchModel = Joi.object({
-    department: Joi.string().uuid().required()
+    id: Joi.string().uuid().required().messages({
+        'any.required': 'User ID is required',
+        'string.empty': 'User ID must not be empty',
+        'string.uuid': 'User ID must be a valid UUID'
+    })
 });
 
 module.exports = UserDepartmentPatchModel;
diff --git a/UC/backend/src/models/usersLoginModel.js b/UC/backend/src/models/usersLoginModel.js
index 95f8156..880a0c0 100644
--- a/UC/backend/src/models/usersLoginModel.js
+++ b/UC/backend/src/models/usersLoginModel.js
@@ -1,8 +1,15 @@
 const Joi = require('joi');
 
 const usersLoginModel = Joi.object({
-    email: Joi.string().email().required(),
-    password: Joi.string().required()
+    email: Joi.string().email().required().messages({
+        'any.required': 'Email is required',
+        'string.empty': 'Email must not be empty',
+        'string.email': 'Email must be a valid email address'
+    }),
+    password: Joi.string().required().messages({
+        'any.required': 'Password is required',
+        'string.empty': 'Password must not be empty'
+    })
 });
 
 module.exports = usersLoginModel;
\ No newline at end of file
diff --git a/UC/backend/src/models/usersModifyModel.js b/UC/backend/src/models/usersModifyModel.js
index cbcb5d2..5820256 100644
--- a/UC/backend/src/models/usersModifyModel.js
+++ b/UC/backend/src/models/usersModifyModel.js
@@ -1,9 +1,21 @@
 const Joi = require('joi');
 
 const usersModifyModel = Joi.object({
-    name: Joi.string().required(),
-    email: Joi.string().email().required(),
-    password: Joi.string().min(8).max(20).required()
+    name: Joi.string().required().messages({
+        'any.required': 'User name is required',
+        'string.empty': 'User name must not be empty'
+    }),
+    email: Joi.string().email().required().messages({
+        'any.required': 'User email is required',
+        'string.empty': 'User email must not be empty',
+        'string.email': 'User email must be a valid email address'
+    }),
+    password: Joi.string().min(8).max(20).required().messages({
+        'any.required': 'Password is required',
+        'string.empty': 'Password must not be empty',
+        'string.min': 'Password must be at least {#limit} characters long',
+        'string.max': 'Password must be at most {#limit} characters long'
+    })
 });
 
 module.exports = usersModifyModel;
\ No newline at end of file
diff --git a/UC/backend/src/models/usersRegisterModel.js b/UC/backend/src/models/usersRegisterModel.js
index 29d13c8..cef077a 100644
--- a/UC/backend/src/models/usersRegisterModel.js
+++ b/UC/backend/src/models/usersRegisterModel.js
@@ -1,10 +1,26 @@
 const Joi = require('joi');
 
 const usersRegisterModel = Joi.object({
-    name: Joi.string().required(),
-    email: Joi.string().email().required(),
-    password: Joi.string().min(8).max(20).required(),
-    department: Joi.string().uuid().required()
+    name: Joi.string().required().messages({
+        'any.required': 'User name is required',
+        'string.empty': 'User name must not be empty'
+    }),
+    email: Joi.string().email().required().messages({
+        'any.required': 'Email is required',
+        'string.empty': 'Email must not be empty',
+        'string.email': 'Email must be a valid email address'
+    }),
+    password: Joi.string().min(8).max(20).required().messages({
+        'any.required': 'Password is required',
+        'string.empty': 'Password must not be empty',
+        'string.min': 'Password must be at least {#limit} characters long',
+        'string.max': 'Password must be at most {#limit} characters long'
+    }),
+    department: Joi.string().uuid().required().messages({
+        'any.required': 'Department ID is required',
+        'string.empty': 'Department ID must not be empty',
+        'string.uuid': 'Department ID must be a valid UUID'
+    })
 });
 
 module.exports = usersRegisterModel;
\ No newline at end of file
diff --git a/UC/backend/src/routes/users.js b/UC/backend/src/routes/users.js
index b871e98..b7f4b5c 100644
--- a/UC/backend/src/routes/users.js
+++ b/UC/backend/src/routes/users.js
@@ -1,34 +1,171 @@
 const express = require('express');
+const { v4: uuidv4 } = require('uuid');
+
+const {schemas} = require('../models/schemaMapper');
+const {httpStatus} = require("../helpers/httpResponses");
+
 const router = express.Router();
 
 function validateBody(req, res, next) {
+    let validationSchema = undefined;
+
+    switch(req.path){
+        case '/register':
+            validationSchema = schemas.usersRegisterModelSchema;
+            break;
+        case '/login':
+            validationSchema = schemas.usersLoginModelSchema;
+            break;
+        case '/validate_email':
+            validationSchema = schemas.emailVerificationSchema;
+            break;
+        case '/':
+            if(req.method === 'PUT'){
+                validationSchema = schemas.usersModifyModelSchema;
+            }
+            break;
+        case 'change_department':
+            validationSchema = schemas.userDepartmentPatchSchema;
+            break;
+        default:
+            validationSchema = undefined;
+    }
+
+    console.log(validationSchema);
+
+    if(validationSchema !== undefined){
+        const {error} = validationSchema.validate(req.body);
+        if(error){
+            const errorMessage = error.details.map(detail => detail.message).join(', ');
+            return res.status(httpStatus.BAD_REQUEST).json({ message: errorMessage });
+        }
+    }
     next();
 }
 
 router.post('/register', validateBody, (req, res) => {
+    const usersDB = req.app.get('usersDB');
+    const usersJson = usersDB.readFile();
+
     const { name, email, password, department } = req.body;
+    const hashedPassword = crypto.createHash('sha256').update(password).digest('hex');
+
+    const newUser = {
+        id: uuidv4(),
+        name: name,
+        email: email,
+        password: hashedPassword,
+        department: department
+    }
+
+    usersJson.push(newUser);
+    usersDB.writeFile(usersJson);
+
+    return res.status(httpStatus.CREATED).json({message: "User successfully created.", data: newUser});
 });
 
 router.post('/login', validateBody, (req, res) => {
+    const usersDB = req.app.get('usersDB');
     const { email, password } = req.body;
+    const hashedPassword = crypto.createHash('sha256').update(password).digest('hex');
+
+    if(usersDB.findIndexByKeyValueInArray('email', email) !==
+    usersDB.findIndexByKeyValueInArray('password', hashedPassword)){
+        return res.status(httpStatus.NOT_FOUND).json({message: 'Invalid credentials.'});
+    }
+
+    return res.status(httpStatus.Ok).json({message: 'Logged in.'});
 });
 
-router.post('/email-validation', validateBody, (req, res) => {
+router.post('/validate_email', validateBody, (req, res) => {
+    const usersDB = req.app.get('usersDB');
     const { email } = req.body;
+
+    if(usersDB.isKeyValue("email", email)){
+        return res.status(httpStatus.CONFLICT).json({"message": "Email already in system."});
+    }
+
+    return res.status(httpStatus.OK).json({"message": "Email is valid."});
 });
 
 router.get('/', (req, res) => {
+    const usersDB = req.app.get('usersDB');
+    return res.status(httpStatus.OK).json({
+        message: "Fetched users",
+        data: usersDB.readFile()
+    })
 });
 
 router.put('/', validateBody, (req, res) => {
+    const usersDB = req.app.get('usersDB');
+    let usersJson = usersDB.readFile();
+
     const { name, email, password } = req.body;
+    const userIndex = usersDB.findIndexByKeyValueInArray('email', email);
+    if(userIndex === -1){
+        return res.status(httpStatus.NOT_FOUND).json({message: 'User not found.'});
+    }
+
+    const hashedPassword = crypto.createHash('sha256').update(password).digest('hex');
+    let userInfo = usersJson[userIndex];
+    userInfo = {
+        id: userInfo.id,
+        name: name,
+        email: email,
+        password: hashedPassword,
+        department: userInfo.department
+    }
+
+    usersJson[userIndex] = userInfo;
+    usersDB.writeFile(usersJson);
+
+    return res.status(httpStatus.OK).json({message: 'Information modified'});
 });
 
-router.patch('/change-department', validateBody, (req, res) => {
+router.patch('/change_department', validateBody, (req, res) => {
+    const usersDB = req.app.get('usersDB');
     const { id, department } = req.body;
+
+    const userIndex = usersDB.findIndexByKeyValueInArray('id', id);
+    if(userIndex === -1){
+        return res.status(httpStatus.NOT_FOUND).json({message: "User not found."});
+    }
+
+    let usersJson = usersDB.readFile();
+    let userInfo = usersJson[userIndex];
+
+    userInfo = {
+        id: userInfo.id,
+        name: userInfo.name,
+        email: userInfo.email,
+        password: userInfo.password,
+        department: department
+    }
+
+    usersJson[userIndex] = userInfo
+    usersDB.writeFile(usersJson);
+
+    return res.status(httpStatus.Ok).json({message: "Department modified."});
 });
 
 router.get('/get_decrypt_keys', (req, res) => {
+    const ceoDB = req.app.get('ceoDB');
+    const departmentsDB = req.app.get('departmentsDB');
+    const ceoPassword = req.headers['ceo_password'];
+    const {password} = ceoDB.readFile()
+
+    if(ceoPassword !== password){
+        return res.status(httpStatus.UNAUTHORIZED).json({message: 'Invalid CEO password.'});
+    }
+
+    return res.status(httpStatus.OK).json({
+        message: 'Departments fetched.',
+        data: departmentsDB.readFile()
+    })
 });
 
+router.use((req, res) => {
+    return res.status(httpStatus.NOT_FOUND).json({message: "Endpoint not found"});
+})
+
 module.exports = router;
diff --git a/UC/frontend/public/js/main_menu.js b/UC/frontend/public/js/main_menu.js
index 02f25ca..70dff71 100644
--- a/UC/frontend/public/js/main_menu.js
+++ b/UC/frontend/public/js/main_menu.js
@@ -70,7 +70,8 @@ document.addEventListener('DOMContentLoaded', function() {
         fetch(endpoint, {
             method: 'GET',
             headers: {
-                'Authorization': id
+                'Authorization': id,
+                'x-api-key': "uc_api"
             },
         })
             .then(async response => {
@@ -116,7 +117,8 @@ document.addEventListener('DOMContentLoaded', function() {
         fetch(endpoint, {
             method: 'GET',
             headers: {
-                'Authorization': id
+                'Authorization': id,
+                'x-api-key': "uc_api"
             },
         })
             .then(async response => {
@@ -162,7 +164,8 @@ document.addEventListener('DOMContentLoaded', function() {
         fetch(endpoint, {
             method: 'GET',
             headers: {
-                'Authorization': id
+                'Authorization': id,
+                'x-api-key': "uc_api"
             },
         })
             .then(async response => {