diff --git a/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/App.xaml.cs b/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/App.xaml.cs
index c640ba3..08c9be0 100644
--- a/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/App.xaml.cs
+++ b/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/App.xaml.cs
@@ -1,4 +1,5 @@
 using System;
+using SafeMessageStorage.Encryption.Hash.Providers;
 using SafeMessageStorage.Pages;
 using SafeMessageStorage.Services.AuthorizationService;
 using Xamarin.Forms;
@@ -11,7 +12,7 @@ namespace SafeMessageStorage
         public App()
         {
             InitializeComponent();
-            MainPage = new NavigationPage(new AuthorizationPage(new AuthorizationServiceMOCK()));
+            MainPage = new NavigationPage(new AuthorizationPage(new AuthorizationService(new Sha256HashProvider())));
         }
 
         protected override void OnStart()
diff --git a/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/Encryption/Hash/HashProviderBase.cs b/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/Encryption/Hash/HashProviderBase.cs
new file mode 100644
index 0000000..2836dd8
--- /dev/null
+++ b/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/Encryption/Hash/HashProviderBase.cs
@@ -0,0 +1,48 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Security.Cryptography;
+using System.Text;
+
+namespace SafeMessageStorage.Encryption.Hash
+{
+    public abstract class HashProviderBase : IHashProvider
+    {
+        private readonly HashAlgorithm _hashAlgorithm;
+
+        protected HashProviderBase(HashAlgorithm hashAlgorithm)
+        {
+            _hashAlgorithm = hashAlgorithm;
+        }
+
+        public virtual string GetHashString(string input)
+        {
+            return GetHashString(Encoding.UTF8.GetBytes(input));
+        }
+
+        public virtual string GetHashString(byte[] bytes)
+        {
+            using (_hashAlgorithm)
+            {
+                return GetHashBytes(bytes)
+                    .Select(b =>
+                        b.ToString("x2"))
+                    .Aggregate((a, b) =>
+                        a + b);
+            }
+        }
+
+        public virtual byte[] GetHashBytes(string input)
+        {
+            return GetHashBytes(Encoding.UTF8.GetBytes(input));
+        }
+
+        public virtual byte[] GetHashBytes(byte[] bytes)
+        {
+            using (_hashAlgorithm)
+            {
+                return _hashAlgorithm.ComputeHash(bytes);
+            }
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/Encryption/Hash/IHashProvider.cs b/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/Encryption/Hash/IHashProvider.cs
new file mode 100644
index 0000000..0dffb71
--- /dev/null
+++ b/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/Encryption/Hash/IHashProvider.cs
@@ -0,0 +1,17 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace SafeMessageStorage.Encryption.Hash
+{
+    public interface IHashProvider
+    {
+        string GetHashString(string input);
+
+        string GetHashString(byte[] bytes);
+
+        byte[] GetHashBytes(string input);
+
+        byte[] GetHashBytes(byte[] bytes);
+    }
+}
diff --git a/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/Encryption/Hash/Providers/Sha256HashProvider.cs b/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/Encryption/Hash/Providers/Sha256HashProvider.cs
new file mode 100644
index 0000000..2b12609
--- /dev/null
+++ b/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/Encryption/Hash/Providers/Sha256HashProvider.cs
@@ -0,0 +1,14 @@
+using System;
+using System.Collections.Generic;
+using System.Security.Cryptography;
+using System.Text;
+
+namespace SafeMessageStorage.Encryption.Hash.Providers
+{
+    public class Sha256HashProvider : HashProviderBase
+    {
+        public Sha256HashProvider() : base(new SHA256CryptoServiceProvider())
+        {
+        }
+    }
+}
diff --git a/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/Encryption/Hash/Providers/Sha512HashProvider.cs b/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/Encryption/Hash/Providers/Sha512HashProvider.cs
new file mode 100644
index 0000000..5de6c00
--- /dev/null
+++ b/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/Encryption/Hash/Providers/Sha512HashProvider.cs
@@ -0,0 +1,14 @@
+using System;
+using System.Collections.Generic;
+using System.Security.Cryptography;
+using System.Text;
+
+namespace SafeMessageStorage.Encryption.Hash.Providers
+{
+    public class Sha512HashProvider : HashProviderBase
+    {
+        public Sha512HashProvider() : base(new SHA512CryptoServiceProvider())
+        {
+        }
+    }
+}
diff --git a/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/Pages/AuthorizationPage.xaml b/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/Pages/AuthorizationPage.xaml
index edeaccd..6839fc5 100644
--- a/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/Pages/AuthorizationPage.xaml
+++ b/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/Pages/AuthorizationPage.xaml
@@ -10,7 +10,7 @@
         <StackLayout VerticalOptions="CenterAndExpand" Padding="40">
             <Label Text="Enter your security code"
                    FontSize="23"/>
-            <Entry IsPassword="True" Placeholder="Your hard code"/>
+            <Entry IsPassword="True" Text="{Binding Password}" Placeholder="Your hard code"/>
             <Label x:Name="ErrorMessageLabel"
                    TextColor="#d22"
                    Margin="0,10" HorizontalOptions="Center"/>
diff --git a/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage.csproj b/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage.csproj
index 1bd2277..992183c 100644
--- a/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage.csproj
+++ b/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage.csproj
@@ -11,6 +11,7 @@
   </ItemGroup>
 
   <ItemGroup>
+    <Folder Include="Encryption\Symmetric\" />
     <Folder Include="Views\" />
   </ItemGroup>
 
diff --git a/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/Services/AuthorizationService/AuthorizationService.cs b/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/Services/AuthorizationService/AuthorizationService.cs
new file mode 100644
index 0000000..635bb5d
--- /dev/null
+++ b/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/Services/AuthorizationService/AuthorizationService.cs
@@ -0,0 +1,47 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using System.Threading.Tasks;
+using SafeMessageStorage.Encryption.Hash;
+
+namespace SafeMessageStorage.Services.AuthorizationService
+{
+    public class AuthorizationService : IAuthorizationService
+    {
+        private readonly string _passwordKey = "passwordGUID";
+        private readonly IHashProvider _hashProvider;
+
+        public AuthorizationService(IHashProvider hashProvider)
+        {
+            _hashProvider = hashProvider;
+        }
+
+        public bool IsAuthorized { get; private set; }
+        public bool IsPasswordSet => Xamarin.Essentials.SecureStorage.GetAsync(_passwordKey).Result != null;
+        public async Task<bool> Authorize(string password)
+        {
+            var keyChainPassword = await Xamarin.Essentials.SecureStorage.GetAsync(_passwordKey);
+            var result = keyChainPassword?.Equals(_hashProvider.GetHashString(password)) ?? false;
+            IsAuthorized = result;
+            return result;
+        }
+
+        public Task<bool> Deauthorize()
+        {
+            IsAuthorized = false;
+            return Task.FromResult(true);
+        }
+
+        public async Task<bool> ChangePassword(string currentPassword, string newPassword)
+        {
+            var keyChainPassword = await Xamarin.Essentials.SecureStorage.GetAsync(_passwordKey);
+            var passwordMatch = keyChainPassword?.Equals(_hashProvider.GetHashString(currentPassword)) ?? true;
+
+            if (!passwordMatch)
+                return false;
+
+            await Xamarin.Essentials.SecureStorage.SetAsync(_passwordKey, _hashProvider.GetHashString(newPassword));
+            return true;
+        }
+    }
+}
diff --git a/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/ViewModels/AuthorizationPageViewModel.cs b/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/ViewModels/AuthorizationPageViewModel.cs
index c60d50b..ad48825 100644
--- a/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/ViewModels/AuthorizationPageViewModel.cs
+++ b/src/SafeMessageStorage/SafeMessageStorage/SafeMessageStorage/ViewModels/AuthorizationPageViewModel.cs
@@ -21,18 +21,18 @@ namespace SafeMessageStorage.ViewModels
         public event EventHandler AuthorizationSucceeded;
         public event EventHandler PasswordSetRequested; 
 
-        private string _securityCode;
-        public string SecurityCode
+        private string _password;
+        public string Password
         {
-            get=>_securityCode;
+            get=>_password;
             set
             {
-                _securityCode = value;
+                _password = value;
                 OnPropertyChanged();
             }
         }
 
-        public ICommand AuthorizeCommand => new Command(async () => await Authorize(SecurityCode));
+        public ICommand AuthorizeCommand => new Command(async () => await Authorize(Password));
 
         public void Initialize()
         {
@@ -47,7 +47,7 @@ namespace SafeMessageStorage.ViewModels
             else
             {
                 AuthorizationFailed?.Invoke(this, "Invalid code");
-                SecurityCode = string.Empty;
+                Password = string.Empty;
             }
         }
     }