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    Critical Thought

    Critical thoughts on quantum technologies

    Signal Bolsters Security with Post-Quantum Cryptography

    ByThemba Hadebe

    Nov 16, 2023
    Signal Bolsters Security with Post-Quantum Cryptography

    Signal, the renowned encrypted messaging platform, is taking bold measures to fortify the security of its platform against potential quantum computing threats. The Signal Foundation, the non-profit organization responsible for developing the Signal messaging app, has recently unveiled an upgraded version of its Extended Triple Diffie-Hellman (X3DH) specification. This upgraded protocol, known as PQXDH, leverages post-quantum cryptography to safeguard against the possibility of quantum computers rendering current cryptographic systems obsolete.

    Quantum computing, although not an immediate concern, poses a significant risk to the integrity of public-key cryptography utilized by Signal. In theory, once quantum computers attain sufficient computational power, they could potentially compute private keys from public keys, thereby compromising the security of encrypted messages.

    Signal’s implementation of post-quantum cryptography is a proactive measure aimed at addressing potential security breaches. It aims to counter a strategy known as ‘harvest now, decrypt later,’ where attackers store encrypted data, anticipating it may be cracked in the future. Although quantum computers may not surpass classical computers in all computational aspects, they possess exceptional capabilities in specific domains, leading to discussions around the concept of ‘quantum supremacy.’

    Shor’s Algorithm, an early illustration of the advantages offered by quantum computing, can efficiently find the prime factors of large numbers. This poses a significant threat to the one-way functions employed by cryptographic systems like RSA, undermining the security of public-key cryptography.

    To mitigate these concerns, Signal has upgraded its protocol from X3DH to PQXDH. This new protocol computes a shared secret for private communication sessions by combining the elliptic curve key agreement protocol X25519 with the post-quantum key encapsulation mechanism CRYSTALS-Kyber, as recommended by the US National Institute of Standards and Technology (NIST).

    By integrating these two shared secrets, Signal enhances its security measures, compelling potential attackers to bypass both X25519 and CRYSTALS-Kyber to gain access to the shared secret. This dual-system approach was adopted due to the realization that one of the quantum-resistant standards recommended by NIST was vulnerable to classical computers.

    It is crucial to note that Signal’s PQXDH protocol primarily aims to safeguard against the ‘harvest now, decrypt later’ scenario and does not offer protection against active quantum attackers. In simpler terms, it cannot impede a malicious server equipped with a quantum computer from generating new key pairings and intercepting encrypted communications.

    The new quantum-resistant protocol has already been incorporated into Signal’s latest versions, ensuring that users can continue to communicate securely in a world where quantum computing capabilities continue to evolve.

    Frequently Asked Questions (FAQ)

    1. What is post-quantum cryptography?
    Post-quantum cryptography refers to cryptographic systems that can withstand attacks from quantum computers. It aims to provide security even when quantum computers become powerful enough to break traditional cryptographic systems.

    2. What is the ‘harvest now, decrypt later’ strategy?
    The ‘harvest now, decrypt later’ strategy involves storing encrypted data with the expectation that it will become vulnerable to decryption in the future when more advanced technology or computational power is available.

    3. What is quantum supremacy?
    Quantum supremacy refers to the hypothetical point at which quantum computers surpass classical computers in performing specific tasks or computations. It sparks debates and discussions about the potential advantages of quantum computing.

    4. Why is Shor’s Algorithm a threat to public-key cryptography?
    Shor’s Algorithm, one of the notable achievements in quantum computing, has the ability to efficiently find the prime factors of large numbers. This poses a threat to the security of public-key cryptography, which relies on the difficulty of factoring large numbers.

    – [US National Institute of Standards and Technology (NIST)](https://www.nist.gov/)