TITUS -- Totally Isolated TLS Unwrapping Server
===============================================
titus is a highly secure network proxy that terminates TLS (SSL)
connections and forwards the unencrypted traffic to some backend.
It is similar in purpose to stud and stunnel.
titus provides heightened security by running in extreme isolation.
The private key is stored in a dedicated process that doesn't talk to
the network, and all private key operations take place in this process.
Furthermore, every connection is handled by a new process that runs
as an unprivileged user in an unwritable and empty root directory.
These security features ensure that if there is a vulnerability in the
TLS processing code, it is very, very unlikely that an attacker could
steal your private key, access the memory of your application, sniff
data from other TLS connections, or otherwise attack your system.
titus aims to be as transparent as possible to the backend application.
Changes to the connection state between the client and titus are reflected
in the connection between titus and the backend, and vice-versa. This
allows the backend to dictate throttling behavior, maximum connection
behavior, and so on.
On Linux, titus can operate in transparent proxy mode so that the client
IP address is preserved when contacting the backend. This requires
special configuration with iptables and advanced routing (see TRANSPARENT
PROXY MODE in the titus(8) man page).
titus supports the Elliptic Curve Diffie-Hellman handshake, and also
provides advanced control over TLS settings, such as the Diffie-Hellman
modulus, and the curve used for Elliptic Curve Diffie-Hellman. This is
handy if your backend's built-in TLS support is lacking.
For technical details about titus' design, see
https://www.agwa.name/blog/post/protecting_the_openssl_private_key_in_a_separate_process
and https://www.agwa.name/blog/post/titus_isolation_techniques_continued
CURRENT STATUS
titus is no longer developed. Since titus was first released, memory-safe
TLS stacks like Go's crypto/tls and Rust's rustls have matured enough that
the author no longer needs titus.
The last version of titus was 0.4, released on 2020-10-27.
NON-LINUX WARNING
On non-Linux systems, due to the lack of the prctl() syscall, titus cannot
prevent tracing/debugging of one titus process by another titus process.
This substantially reduces the isolation between TLS connections, although
private key operations remain isolated since they run as a separate user.
On FreeBSD 10.2-RELEASE and higher, titus uses procctl with PROC_TRACE_CTL
to disable tracing, which should provide isolation. However, this has
not undergone security analysis yet and should be considered experimental.
INSTALLING TITUS
To build from source, see the BUILDING file.
CONFIGURING TITUS
Start with titus.conf.example and modify it to fit your needs. Also see
the titus(8) man page.
If you're using the Debian package, start with the example config
in /usr/share/doc/titus/examples and place it in /etc/titus.
See /etc/titus/README for details.
RUNNING TITUS
Run `titus --config /path/to/titus.conf`.
FURTHER DOCUMENTATION
* For copyright/license, see COPYING.
* For build instructions, see BUILDING.
* For general documentation, see the titus(8) man page.
