# Signal Protocol Gets Quantum-Resistant Upgrade

SPQR enhances security against future quantum threats.

- **Source:** [Signal Blog](https://signal.org/blog)
- **Published:** 2025-10-02
- **Topic:** [Software & Engineering](https://brifing.si/c/engineering)
- **Original article:** <https://signal.org/blog/spqr/>
- **On Brifing:** https://brifing.si/s/77bfce5f-c20d-439a-bf49-0b49ba9d16c7

## A New Step for the Signal Protocol

The Signal Protocol has introduced a new mechanism called Sparse Post Quantum Ratchet (SPQR) to enhance security against future quantum computing threats. This update maintains existing security guarantees while adding quantum resistance.

## What is SPQR?

SPQR is a quantum-resistant ratchet mechanism added to the Signal Protocol. It ensures both Forward Secrecy (FS) and Post-Compromise Security (PCS) in a quantum-safe manner.

## What Changes for Users?

Signal users will experience no changes in the app. However, all conversations will automatically transition to the new protocol without requiring any user action.

## Forward Secrecy and Post-Compromise Security

Forward Secrecy (FS) protects past messages against future compromises, while Post-Compromise Security (PCS) protects future messages from past compromises.

## ECDH and Quantum Threats

The current Signal Protocol uses hash functions for Forward Secrecy and elliptic-curve Diffie Hellman (ECDH) for Post-Compromise Security. However, ECDH is not resistant to quantum computers.

## SPQR and the Triple Ratchet

SPQR is combined with the existing Double Ratchet mechanism to create a new combination called the Triple Ratchet. This combination enhances quantum resistance while maintaining existing security guarantees.

## The Impact of Quantum Computers

If an attacker gains access to a quantum computer, the secret keys generated using elliptic-curve cryptography could be decrypted. In such a case, the current security mechanisms of the Signal Protocol would be insufficient.

## The Importance of SPQR

SPQR enhances the security of the Signal Protocol against future quantum threats. This ensures that users' communications are protected both now and in the future.

## The Future of the Signal Protocol

The Signal Protocol continues to take pioneering steps in quantum resistance. Updates like SPQR prepare it for future technological advancements.

## Security for Users

Signal users will be protected against both current and future quantum threats thanks to SPQR. This update will automatically take effect without requiring any user action.

## Technical Details

SPQR is integrated into the technical specifications of the Signal Protocol. This update is explained in detail on Signal's documentation site.

## Preparing for the Future

The Signal Protocol is proactively preparing for the threats posed by quantum computers. Updates like SPQR are crucial steps in meeting future security needs.

## Sources covering this story

- https://signal.org/blog/spqr/ — 

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_Summary written by Brifing from the original reporting. Copyright in the original article belongs to its publisher; read the full piece at the link above._