PQConnect: Security

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PQConnect: Security

## Cooperative security

PQConnect is not in competition with existing application-specific cryptographic layers, such as TLS and SSH. PQConnect adds an extra cryptographic layer as an application-independent "bump in the wire" in the network stack. Deploying PQConnect means that the attacker has to break PQConnect and has to break whatever cryptographic mechanisms the application provides. This layering has an important effect on security decisions, as explained below.

## Primum non nocere

Modifying cryptography often damages security. This damage can easily outweigh whatever advantages the modification was intended to have. For example, upgrading from ECC to SIKE was claimed to solidly protect against quantum computers, but SIKE was shown 11 years after its introduction to be efficiently breakable. There are many other examples of broken post-quantum proposals; out of 69 round-1 submissions to the NIST Post-Quantum Cryptography Standardization Project, 48% are now known to not reach their security goals, including 25% of the submissions that were not broken at the end of round 1 and 36% of the submissions that were selected by NIST for round 2. As another example, OCB2, which was claimed to be an improvement over OCB1, was shown 15 years after its introduction to be efficiently breakable.

However, for an extra layer of security, the risk analysis is different. A collapse of the extra layer of security simply reverts to the previous situation, the situation without that layer.

We are not saying that it doesn't matter whether PQConnect is secure. We have tried hard to make sure that PQConnect is secure by itself, protecting applications that make unencrypted connections or that use broken encryption. We are continuing efforts to to improve the level of assurance of PQConnect, and we encourage further analysis.

What we are saying is that, beyond being designed for security benefits, PQConnect is designed to minimize security risks.

Beyond the basic structure of PQConnect as a new security mechanism, the rest of this page describes some PQConnect software features aimed at making sure that PQConnect will not damage existing security even if something goes horribly wrong. There is a separate page regarding PQConnect's cryptographic goals.

## Virtualization

System administrators often run hypervisors such as Xen to isolate applications inside virtual machines. The PQConnect software supports client-in-a-bottle and server-in-a-bottle modes. In these modes, the PQConnect software runs inside a virtual machine while protecting connections to and from the entire system. The overall data flow of network traffic is similar to what would happen if PQConnect handling were delegated to an external router, but the router is within the same machine, limiting opportunities for attackers to intercept unencrypted traffic.

Beware that virtual machines are not perfect isolation. For example, various Xen security holes have been discovered, and timing attacks have sometimes been demonstrated reading data from other virtual machines.

## Memory safety

The PQConnect software is written in Python with careful use of libraries. Using high-level languages such as Python limits the level of assurance of constant-time data handling and key erasure, but these are not memory-safety risks.

Cryptographic operations are carried out via libraries that follow the SUPERCOP/NaCl API, rather than libraries whose APIs inherently require dynamic memory allocation. The relevant library code has been systematically tested under memory checkers such as valgrind. Memory checkers do not necessarily exercise all code paths, but all data flow from attacker-controlled inputs to branches or memory addresses is avoided in the specific public-key cryptosystems used in PQConnect.

## File safety

The PQConnect software is primarily memory-based. The filesystem is used in a few limited ways (e.g., storing the server's long-term keys), with no data flow from attacker-controlled inputs.

## Port security

Malicious users on a multi-user machine, or attackers compromising applications, can bind to specific TCP ports or UDP ports, preventing PQConnect from using those ports. However, the operating system prevents non-root users from binding to ports below 1024, so you can simply choose ports below 1024 for running PQConnect. For example, you are probably not using port 584 ("keyserver") or port 624 ("cryptoadmin") for anything else; you can use those for a PQConnect server.

## Privilege separation

Privileges are used at run time by the PQConnect software components that hook into the networking stack and that create and read/write packets on the TUN network interface. The PQConnect software employs privilege separation to isolate code that requires these privileges from the rest of the software. Most of the code is run in a process as a non-root `pqconnect` user. Untrusted data arriving on the network is piped from the root process to the non-root process for handling.

## Privilege limitation

When the PQConnect software is run under systemd (as currently recommended), various external constraints are applied to the system calls used by the software, although this is generally less limiting than running in a virtual machine.

Version: This is version 2024.12.26 of the "Security" web page.