add totp in security/ssh

Security/README.md

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+<header><h1>
+Security
+</h1></header>

Security/SSH/README.md

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+<header><h1>
+SSH
+</h1></header>
+
+# Add TOTP on ssh connection
+For a more secure ssh connection, you can add TOTP (Time-based One-Time Password) to your ssh connection.
+This will require you to enter a password and a TOTP code to connect to your server.
+This is a good way to add an extra layer of security to your server.
+
+## Installing Google Authenticator PAM
+```bash
+sudo apt install libpam-google-authenticator
+```
+## Configuring SSHD for Google PAM
+1. Edit the sshd configuration file
+    ```bash
+    sudo nano /etc/pam.d/sshd
+    ```
+2. Modified the file to look like this
+   ```bash
+   # PAM configuration for the Secure Shell service
+
+   # Standard Un*x authentication.
+   #@include common-auth
+   
+   . . .
+   
+   # Standard Un*x password updating.
+   @include common-password
+   auth required pam_google_authenticator.so nullok
+   ```
+   Comment out the `@include common-auth` for disable password authentication.
+   `nullok` allows users without a TOTP code to connect without one.
+3. Edit the sshd configuration file
+    ```bash
+    sudo nano /etc/ssh/sshd_config
+    ```
+4. Add the following line to the bottom of the file
+   ```bash
+   . . .
+   # Change to yes to enable challenge-response passwords (beware issues with
+   # some PAM modules and threads)
+   ChallengeResponseAuthentication yes
+   . . .
+   UsePAM yes
+   AuthenticationMethods publickey,password publickey,keyboard-interactive
+   . . .
+   ```
+5. Restart the sshd service
+    ```bash
+    sudo systemctl restart sshd
+    ```
+   
+## Generating the Google Authenticator QR Code
+1. Run the following command
+    ```bash
+    google-authenticator
+    ```
+2. Answer the following questions
+3. Scan the QR code with your Google Authenticator app
+4. Save the emergency scratch codes in a safe place
+5. Restart the sshd service
+    ```bash
+    sudo systemctl restart sshd
+    ```
+