• Wed. Nov 29th, 2023

    Critical Thought

    Critical thoughts on quantum technologies

    Signal’s Quantum-Resistant Encryption Protocol: Protecting Digital Communication in the Era of Quantum Computing

    ByByron Bekker

    Nov 20, 2023
    Signal’s Quantum-Resistant Encryption Protocol: Protecting Digital Communication in the Era of Quantum Computing

    Signal, a renowned messaging platform known for its high level of security, is taking a proactive step towards preparing for the quantum computing revolution. With the advent of quantum computing, traditional encryption and security standards are at risk of becoming obsolete. However, Signal is not sitting idly by; the company has recently unveiled a brand-new protocol that is specifically designed to be resistant to the threats posed by quantum computers.

    In a recent blog post, Signal announced the development of their latest protocol upgrade, known as PQXDH, which is an enhancement to the existing X3DH specification. This upgrade provides an extra layer of protection against the hypothetical future scenario where a powerful quantum computer could potentially break the current encryption norms that we rely on.

    The innovative approach taken by Signal involves the integration of new post-quantum cryptosystems that utilize one-way functions which cannot be reversed efficiently by quantum computers. These new cryptosystems have been developed thanks to the relentless efforts of cryptographic researchers and the NIST Standardization Process for Post-Quantum Cryptography, which has garnered immense community input from domain experts.

    While adopting the new protocol, Signal is not entirely replacing its existing elliptic curve cryptography foundations. Instead, the company is adopting a hybrid approach, combining the new post-quantum cryptosystems with their current systems. This strategy ensures that an attacker would need to successfully breach both the existing elliptic curve cryptography and the post-quantum public key cryptosystem to gain access to the keys used for safeguarding users’ communications. By doing so, Signal is creating a more robust and secure system that raises the bar for potential attackers.

    The crux of Signal’s protocol upgrade lies in its ability to compute a shared secret between parties engaged in a private communication session. This shared secret, known only to the participants involved, is computed by utilizing both the X25519 elliptic curve key agreement protocol and the CRYSTALS-Kyber post-quantum key encapsulation mechanism. By combining these two shared secrets, Signal ensures that any potential attacker would need to break both the X25519 protocol and the CRYSTALS-Kyber mechanism to obtain the same shared secret, further solidifying the security of users’ data.

    Signal’s dedication to safeguarding digital communication has already been put into practice, with the new protocol being implemented in the latest version of their platform. Users can now benefit from enhanced security measures and enjoy the confidence that their private conversations are shielded from the imminent threats posed by quantum computing.


    Q: What is quantum computing?
    A: Quantum computing is an emerging field of computer science that utilizes the principles of quantum mechanics to perform computations that surpass the capabilities of traditional computers, particularly in solving complex problems.

    Q: Why does quantum computing pose a threat to encryption?
    A: Quantum computers have the potential to break traditional encryption algorithms by exploiting the computational power of quantum bits (qubits) and leveraging their ability to perform calculations much faster than classical computers.

    Q: What is post-quantum cryptography?
    A: Post-quantum cryptography refers to cryptographic algorithms and protocols specifically designed to resist attacks from quantum computers and preserve the confidentiality and integrity of data in the face of quantum threats.

    Q: What are one-way functions?
    A: One-way functions are mathematical operations or algorithms that are easy to compute in one direction but computationally difficult to reverse. They are widely used in encryption to secure data by making it challenging to retrieve the original information from its encrypted form.

    – Signal Blog: https://signal.org/blog/advanced-ratcheting/