NCSC urges immediate SSL and TLS 1.0/1.1 disablement, mandates TLS 1.3 for post-quantum readiness

The UK National Cyber Security Centre has published new guidance on configuring Transport Layer Security to protect data and transition to post-quantum cryptography. The advisory targets system administrators responsible for server and client estates, outlining secure profiles for common scenarios. It emphasises the necessity of disabling deprecated protocols and managing certificates effectively. The guidance aims to help organisations mitigate risks from both classical and future quantum computing threats.

Root cause

The primary driver for this update is the emerging threat from cryptographically relevant quantum computers. These systems threaten the key exchange and digital signature algorithms currently securing TLS communications. The NCSC notes that while TLS 1.2 offers strong protection against classical attacks, it will not receive new features beyond critical updates. Consequently, organisations must plan a transition to TLS 1.3 to adopt post-quantum cryptographic standards.

Attack path

A quantum computer could compromise the confidentiality of data protected by current TLS implementations. The risk lies in the ability to break existing key exchange mechanisms. The NCSC states that only TLS 1.3, when configured correctly, provides protection against such quantum attacks. Older versions like TLS 1.1 and 1.0 are deprecated and considered insecure, leaving systems vulnerable to eavesdropping and tampering if not disabled.

Affected versions

• All versions of the Secure Sockets Layer (SSL) protocol
• TLS 1.0 and TLS 1.1
• TLS 1.2 systems not planned for migration to TLS 1.3
• Services relying on public Web PKI without post-quantum authentication

Mitigation

• Disable all SSL versions and TLS 1.0 and 1.1 immediately.
• Configure TLS 1.3 using the NCSC’s recommended cryptographic profiles.
• Develop a plan to migrate TLS 1.2 services to TLS 1.3.
• Use hybrid post-quantum/traditional key agreement mechanisms as an interim measure.

What it means for organisations

Teams usually need to audit their server configurations to identify legacy protocol usage. Security leads should verify that TLS 1.3 is enabled and that older versions are disabled across all endpoints. Organisations must assess their supplier base to ensure third-party services meet these standards. Internal communications should inform developers of the need to plan for post-quantum migration. Risk managers should review current encryption strategies to align with these updated guidelines.

What to do and how to stay safe: NCSC

• Review server configurations to ensure TLS 1.0, 1.1, and all SSL versions are disabled.
• Verify that TLS 1.3 is enabled and configured with recommended cryptographic profiles.
• Check supplier contracts and service level agreements for compliance with modern TLS standards.
• Monitor vendor updates for mature implementations of post-quantum authentication standards.

General security guidance from the TechSec Observer newsroom. It is not confirmed advice from the organisations named in this story.

Frequently asked questions

Which TLS version provides protection against quantum attacks?

Only TLS 1.3 provides protection against quantum attacks when configured correctly according to the NCSC guidance.

Should I continue using TLS 1.2?

TLS 1.2 is still considered secure against classical attacks but will not receive new features; you should plan to migrate to TLS 1.3.

Are post-quantum authentication standards finalised?

No, the IETF is still developing standards for post-quantum authentication in TLS and the wider Web PKI.