enhances misc security settings

The following settings are changed:

deactivates previews in Dolphin; deactivates previews in Nautilus; deactivates TCP timestamps; deactivates Netfilter's connection tracking helper;

TCP time stamps (RFC 1323) allow for tracking clock information with millisecond resolution. This may or may not allow an attacker to learn information about the system clock at such a resolution, depending on various issues such as network lag. This information is available to anyone who monitors the network somewhere between the attacked system and the destination server. It may allow an attacker to find out how long a given system has been running, and to distinguish several systems running behind NAT and using the same IP address. It might also allow one to look for clocks that match an expected value to find the public IP used by a user.

Hence, this package disables this feature by shipping the /etc/sysctl.d/tcp_timestamps.conf configuration file.

Note that TCP time stamps normally have some usefulness. They are needed for:

• the TCP protection against wrapped sequence numbers; however, to trigger a wrap, one needs to send roughly 2^32 packets in one minute: as said in RFC 1700, "The current recommended default time to live (TTL) for the Internet Protocol (IP) [45,105] is 64". So, this probably won't be a practical problem in the context of Anonymity Distributions.

• "Round-Trip Time Measurement", which is only useful when the user manages to saturate their connection. When using Anonymity Distributions, probably the limiting factor for transmission speed is rarely the capacity of the user connection.

Netfilter's connection tracking helper module increases kernel attack surface by enabling superfluous functionality such as IRC parsing in the kernel. (!)

Hence, this package disables this feature by shipping the /etc/sysctl.d/nf_conntrack_helper.conf configuration file.

How to install security-misc using apt-get

1. Add Whonix's Signing Key.

sudo apt-key --keyring /etc/apt/trusted.gpg.d/whonix.gpg adv --keyserver hkp://ipv4.pool.sks-keyservers.net:80 --recv-keys 916B8D99C38EAF5E8ADC7A2A8D66066A2EEACCDA

3. Add Whonix's APT repository.

echo "deb http://deb.whonix.org stretch main" | sudo tee /etc/apt/sources.list.d/whonix.list

4. Update your package lists.

sudo apt-get update

5. Install security-misc.

sudo apt-get install security-misc

How to Build deb Package

Replace apparmor-profile-torbrowser with the actual name of this package with security-misc and see instructions.

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