tripwire

Installation

Tripwire’s installation process varies slightly depending on your Linux distribution. However, the general approach involves using your distribution’s package manager. Here are examples for some common distributions:

Debian/Ubuntu:

sudo apt update
sudo apt install tripwire

Fedora/CentOS/RHEL:

sudo dnf install tripwire

Arch Linux:

sudo pacman -S tripwire

Initial Configuration and Database Creation

After installation, you need to initialize Tripwire. This involves creating a policy file and a database of your current file system’s integrity. Any errors here will prevent Tripwire from functioning correctly.

The first step is to install the configuration files. Typically, this involves running a command like this:

sudo tripwire --init

This command will create the necessary configuration files, usually under /etc/tripwire. You’ll likely be prompted to set a root password. Choose a strong and memorable password; this is the password needed to access and manage Tripwire. This password is essential for security; failure to remember it will lock you out.

Next, you need to create the initial Tripwire database. This is done using the tripwire --check command.

sudo tripwire --check

This command will scan your system and create a database containing checksums for the files specified in the policy file. The output shows the status of the scan. You should see a confirmation message if the database creation was successful.

Customizing the Tripwire Policy

Tripwire’s functionality is defined by its policy file, usually located at /etc/tripwire/twpol.txt. This file specifies which files and directories should be monitored. Modifying this file allows for fine-grained control over what Tripwire watches.

By default, /etc/tripwire/twpol.txt includes many essential system files and directories. However, you might want to add or remove entries. For example, to monitor a specific configuration file, you would add a line similar to this:

/etc/apache2/apache2.conf  md5  root  0644

This line specifies:

• /etc/apache2/apache2.conf: The file to monitor.
• md5: The checksum algorithm to use (MD5, SHA-1, SHA-256 are common options).
• root: The expected owner of the file.
• 0644: The expected file permissions.

Important Considerations: Incorrectly modifying the twpol.txt file can lead to false positives. Understand the effects of adding or removing entries from this file.

Running Tripwire and Analyzing Reports

To run a security scan with Tripwire after you’ve made changes, you run:

sudo tripwire --check

Tripwire will compare the current state of your system with the database created earlier. If any changes are detected (e.g., a file has been modified, deleted, or created), Tripwire will generate a report highlighting the discrepancies. This report will usually be located in /var/log/tripwire.

Examining the report is important for determining whether the changes are legitimate or indicate malicious activity.

Working with the Tripwire Report

Tripwire’s reports are crucial, detailing file changes (names, checksums, timestamps). Understanding what constitutes an actual security risk requires careful report examination and correlation with known system changes or updates. False positives—legitimate updates misinterpreted as security breaches—are common and require elimination. A good understanding of your system’s typical operational changes is essential for accurate interpretation.

Utilizing Different Checksum Algorithms

Tripwire supports various checksum algorithms such as MD5, SHA-1, and SHA-256. The choice of algorithm influences the security and performance of the scan. While MD5 is faster, SHA-256 offers better collision resistance and is generally preferred for stronger security. The policy file controls the algorithm used for each file, allowing tailored security based on criticality.