Author: ron (Page 24 of 40)

Configuring Postfix as a Relay

September 15, 2020 / ron / 0 Comments

Installing Postfix

Run the following commands:

sudo apt-get update
sudo apt-get install postfix

Configuring Postfix

Run the following command:
```
sudo dpkg-reconfigure postfix
```
Configuration questions:
1. Select OK to proceed.
2. Choose Satellite system.
3. System Mail Name: <EMAIL_DOMAIN>
4. SMTP relay host: <RELAY_HOST>
  
  Where RELAY_HOST must include the port number (e.g. 192.168.1.1:465).
5. Root and postmaster mail recipient: root
6. Other destinations to accept mail for: <EMAIL_DOMAIN>, localhost.localdomain, localhost
7. Force synchronous updates on mail queue? No
8. Local networks: 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
9. Mailbox size limit (bytes): 0
10. Local address extension character: +
11. Internet protocols to use: all
  
  Feel free to answer the preceding questions based on your setup. Just replace the EMAIL_DOMAIN (i.e. example.com) with a valid value.
Create the file /etc/postfix/sasl_passwd with the following content:
```
<RELAY_HOST> username:password
```
Create a postfix database based on /etc/postfix/sasl_passwd using the following command:
```
sudo postmap /etc/postfix/sasl_passwd
```

Edit the file /etc/postfix/main.cf to have the following entries added or updated:

smtp_tls_security_level = encrypt
smtp_sasl_auth_enable = yes
smtp_tls_wrappermode = yes
smtp_sasl_security_options =
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd

Restart the postfix service with the following command:
```
sudo systemctl restart postfix
```

Blocking/Unblocking IP in Ubuntu

September 14, 2020 / ron / 0 Comments

Pre-requisite

Install the iptables-persistent package to automatically load saved iptables rules.

sudo apt-get install iptables-persistent

Lists the rules in a chain or all chains

sudo iptables -L [CHAIN]

Where CHAIN sample value could be one of the following: INPUT, FORWARD or OUTPUT. If this is not provided all the chains will be listed.

Blocking an IP Address

sudo iptables -A INPUT -s <IP_ADDR> -j DROP
sudo sh -c "iptables-save > /etc/iptables/rules.v4"

Where IP_ADDR is the IP address to be blocked.

Unblocking an IP Address

sudo iptables -D INPUT -s <IP_ADDR> -j DROP
sudo sh -c "iptables-save > /etc/iptables/rules.v4"

Where IP_ADDR is the IP address to be unblocked if you use the preceding blocking procedure.

Useful HTML Entities for Communication

September 3, 2020 / ron / 0 Comments

Entity	Symbol	Description
☎	☎	Black Telephone
☎	☎	Black Telephone
☏	☏	White Telephone
☏	☏	White Telephone
✆	✆	Telephone Location Sign
✆	✆	Telephone Location Sign
✉	✉	Envelope
✉	✉	Envelope

Usefull HTML Entities for Tracking Tasks

August 20, 2020 / ron / 0 Comments

Entity	Display	Description
☐	☐	Ballot box
◻	◻	Empty Box
◻	◻	Empty Box
□	□	Square
□	□	Square
☑	☑	Ballot box with check
✓	✓	Check
✓	✓	Check
☒	☒	Ballot box with cross
⊠	⊠	Box with cross
⊠	⊠	Box with cross
✗	✗	Cross
✗	✗	Cross

Sample Show Balloon Notification for PowerShell

August 17, 2020 / ron / 0 Comments

A sample implementation of windows balloon notification for powershell is as follows:

Add-Type -AssemblyName System.Windows.Forms

function FnShowBalloon {

    [CmdLetBinding()]
    param($title, 
           $message, 
           [string] $icon = 'info', 
           [int] $delay = 20000, 
           [int] $sleep=0)

    Switch($icon.ToString().ToLower()) {
        'warn' {$iconInstance = [System.Windows.Forms.ToolTipIcon]::Warning}
        'error' {$iconInstance = [System.Windows.Forms.ToolTipIcon]::Error}
        'info' {$iconInstance = [System.Windows.Forms.ToolTipIcon]::Info}
        default {$iconInstance = [System.Windows.Forms.ToolTipIcon]::None}
    }

    $notification = New-Object System.Windows.Forms.NotifyIcon
    $path = (Get-Process -id $pid).Path
    $notification.Icon = [System.Drawing.Icon]::ExtractAssociatedIcon($path)
    $notification.BalloonTipIcon = $iconInstance
    $notification.BalloonTipTitle = $title
    $notification.BalloonTipText = $message
    $notification.Visible = $true
    $notification.ShowBalloonTip($delay)

    if ($sleep -gt 0) {
        Start-Sleep -s $sleep
        $notification.Dispose()
    }
}

The FnShowBalloon function can be used as follows:

FnShowBalloon -title "Hello World" -message "This is a sample message" -icon info

Change to the Location of the PowerShell file

August 17, 2020 / ron / 0 Comments

It is recommended to have the following command somewhere in the beginning of the powershell script file:

cd /d $PSScriptRoot

The presence of this will run all the commands after it with respect to the location of the running powershell script file.

Recommended Way to Redirect the Output to a Text File in PowerShell

August 17, 2020 / ron / 0 Comments

Instead of using > to redirect the output into a file, pipe it to out-file cmdlet.

The out-file cmdlet allows some useful parameters as follows:

Parameter	Argument	Description
-Append		Adds the output to the end of an existing file.
-Encoding	Encoding	Specifies the type of encoding for the target file. The default value is utf8NoBOM. The acceptable values for this parameter are as follows: ascii: Uses the encoding for the ASCII (7-bit) character set. bigendianunicode: Encodes in UTF-16 format using the big-endian byte order. oem: Uses the default encoding for MS-DOS and console programs. unicode: Encodes in UTF-16 format using the little-endian byte order. utf7: Encodes in UTF-7 format. utf8: Encodes in UTF-8 format. utf8BOM: Encodes in UTF-8 format with Byte Order Mark (BOM) utf8NoBOM: Encodes in UTF-8 format without Byte Order Mark (BOM) utf32: Encodes in UTF-32 format.
-FilePath	Path	Specifies the path to the output file.

To redirecting the output of the dir command to dir.txt file, use the following command:

dir | out-file -encoding ascii -filepath "dir.txt"

Java 6 to use TLS 1.2 by using BouncyCastle

July 28, 2020 / ron / 0 Comments

Download the Java Cryptography Extension (JCE) Unlimited Strength Jurisdiction Policy Files 6. (i.e. if the link is already dead then download this instead jce_policy-6.)
Extract the downloaded archive and follow the installation procedure found in the README.txt.
Download the following Bouncy Castle libraries:
- bcprov-jdk15to18-166.jar
- bctls-jdk15to18-166.jar
  
  If the preceding links doesn't work try to find them from the archive.
Place the downloaded libraries into ${JAVA_HOME}/jre/lib/ext directory.

Update the java.security (i.e. found in ${JAVA_HOME}/jre/lib/security directory.) file to have the following as the priority:

security.provider.1=org.bouncycastle.jce.provider.BouncyCastleProvider
security.provider.2=org.bouncycastle.jsse.provider.BouncyCastleJsseProvider

Adjust the other security.provider to start from 3 like the following:

security.provider.3=sun.security.provider.Sun
security.provider.4=sun.security.rsa.SunRsaSign
security.provider.5=com.sun.net.ssl.internal.ssl.Provider
security.provider.6=com.sun.crypto.provider.SunJCE
security.provider.7=sun.security.jgss.SunProvider
security.provider.8=com.sun.security.sasl.Provider
security.provider.9=org.jcp.xml.dsig.internal.dom.XMLDSigRI
security.provider.10=sun.security.smartcardio.SunPCSC
security.provider.11=sun.security.mscapi.SunMSCAPI

Try the following Java code:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.ProtocolException;
import java.net.URL;

public class Main {

    public static void main(String[] args) {
        try {
            URL url = new URL("https://www.nist.gov/");
            System.out.println(url);
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setRequestMethod("GET");
            connection.setDoOutput(true);
            System.out.println(connection.getResponseCode());
            StringBuilder response = new StringBuilder();
            BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));

            try {
                String line = reader.readLine();
                while (line != null) {
                    response.append(line);
                    line = reader.readLine();
                }
            } finally {
                reader.close();
            }

            System.out.println(response.toString());
        }
        catch(ProtocolException exception) {
            exception.printStackTrace();
        }
        catch(IOException exception) {
            exception.printStackTrace();
        }
    }
}

You should be able to access it without any SSL handshake error.

Alternatively, you can opt to use the official JDK 6u121 via the Java SE 6 Advanced and Java SE 6 Support if you have availed of it.

Registered Jack 45 (RJ45) Pin Connector Wiring

July 23, 2020 / ron / 0 Comments

T-568A Straight-Through Wiring

T-568B Straight-Through Wiring (Recommended to Use)

T-568A and T-568B Crossover Wiring

Extension Methods

June 23, 2020 / ron / 0 Comments

The method that allows to add methods to existing type without creating a new derived type, recompiling, or otherwise modifying the original type.

A method signature template with a return value and an argument

public static <T_RETURN> <METHOD_NAME>(this <T_TYPE> <VAR_NAME>, <T_ARG1_TYPE> <ARG1_NAME>)

Token	Description
T_RETURN	The type of the return value.
METHOD_NAME	The desired name of the method.
T_TYPE	The existing type to extend.
VAR_NAME	The holder of an instance of the T_TYPE
T_ARG1_TYPE	Type of the first argument.
ARG1_NAME	The name of the first argument.

This method is actually a static method but the first argument has the keyword this and the target type to extend. Also it holds the instance of the target type.

The T_RETURN and the argument part of the template are optional. Also the argument is not limited to just one, you can have as many as required by your extension.

Author: ron (Page 24 of 40)

Configuring Postfix as a Relay

Installing Postfix

Configuring Postfix

Blocking/Unblocking IP in Ubuntu

Pre-requisite

Lists the rules in a chain or all chains

Blocking an IP Address

Unblocking an IP Address

Useful HTML Entities for Communication

Usefull HTML Entities for Tracking Tasks

Sample Show Balloon Notification for PowerShell

Change to the Location of the PowerShell file

Recommended Way to Redirect the Output to a Text File in PowerShell

Java 6 to use TLS 1.2 by using BouncyCastle

Registered Jack 45 (RJ45) Pin Connector Wiring

T-568A Straight-Through Wiring

T-568B Straight-Through Wiring (Recommended to Use)

T-568A and T-568B Crossover Wiring

Extension Methods

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