Feature Request: Explore Post-Quantum Cryptography (PQC) for SimpleLogin

[anhkhoakz]

Summary

I would like to propose that SimpleLogin explore and develop a roadmap for post-quantum cryptography (PQC) to strengthen its long-term security and privacy.

As quantum computing advances, widely used public-key cryptographic algorithms may eventually become vulnerable to sufficiently capable quantum computers. Adopting quantum-resistant cryptography where appropriate would help SimpleLogin prepare for this long-term security risk.

Motivation

SimpleLogin is a privacy-focused email alias service. Since email metadata and communications can contain sensitive information, long-term confidentiality and cryptographic agility are important considerations.

One relevant threat is harvest now, decrypt later: an adversary collects encrypted traffic today and attempts to decrypt it in the future when sufficiently capable quantum computers become available.

Although the practical timeline for cryptographically relevant quantum computers remains uncertain, planning for the transition to post-quantum cryptography before it becomes urgent would be beneficial.

Proposed improvements

1. Assess current cryptographic dependencies. Identify which components rely on public-key algorithms vulnerable to known quantum attacks, including TLS connections, key exchange, and any encryption features supported by SimpleLogin.

2. Evaluate hybrid post-quantum key exchange. Where applicable, consider hybrid key establishment combining classical cryptography with standardized post-quantum algorithms, such as X25519 and ML-KEM (FIPS 203), subject to protocol compatibility and security review.

3. Review email encryption support. Evaluate the long-term implications of the current OpenPGP-based encryption functionality and whether post-quantum-capable OpenPGP implementations could be supported when mature, interoperable implementations are available.

4. Publish a cryptographic migration roadmap. Document the current cryptographic architecture, relevant limitations, planned evaluations, and criteria for adopting post-quantum algorithms.

5. Maintain backward compatibility and interoperability. Any migration should preserve reliable email delivery, avoid unnecessary disruption, and provide a clear transition path for existing users.

Scope and considerations

I am not suggesting an immediate, disruptive migration or claiming that existing encryption is currently broken.

The first step could simply be a security assessment and a public discussion of the project's long-term cryptographic strategy.

It is also important to distinguish transport security from end-to-end encryption. Post-quantum TLS can protect eligible network connections, but it does not automatically provide end-to-end email confidentiality or prevent SimpleLogin from accessing message contents during processing.

Any proposed changes should follow established standards, undergo independent security review, and account for the operational constraints of an email alias service.

Questions for the maintainers

• Has SimpleLogin evaluated the impact of quantum computing on its current cryptographic dependencies?
• Is post-quantum cryptography already on the project's security roadmap?
• Would the maintainers consider publishing a high-level cryptographic migration plan?
• Are there technical or interoperability constraints that currently prevent the adoption of hybrid post-quantum cryptography?

Thank you for maintaining SimpleLogin and for considering its long-term security.