Overview of Security Updates

GitHub has announced comprehensive updates to its platform's cryptographic posture via the [GitHub Changelog](https://github.blog/changelog/2026-09-22-security-improvements-for-ssh/), detailing plans to remove several legacy SSH algorithms, introduce a novel post-quantum key exchange mechanism, and enforce stricter key length mandates for RSA configurations. Further details are available from GitHub Changelog in the original source material.

These updates are designed to safeguard user connections and modernize the cryptographic standards utilized across the infrastructure. The company is actively phasing out older technologies that are known to be weak or susceptible to advanced computational threats, including upcoming developments in quantum computing.

Algorithm Removals and Key Restrictions

As part of the deprecation schedule, GitHub is removing the ability to use RSA keys that rely on SHA-1 in SSH. This encompasses the ssh-rsa signature type, along with any associated ssh-rsa-cert-v01@openssh.com certificates utilizing SHA-1. Additionally, the platform is eliminating the diffie-hellman-group-exchange-sha256 key exchange mechanism due to its slow performance and vulnerability to future quantum computing advances.

Furthermore, all newly uploaded RSA SSH keys created after October 14, 2026, must feature a minimum size of 3072 bits for both signing and authentication purposes. This adjustment is intended to align platform security configurations with modern 128-bit security requirements.

Adoption of Post-Quantum Cryptography

To address future cryptographic threats, GitHub is introducing support for the post-quantum key exchange method known as mlkem768x25519-sha256. This method will be deployed for SSH sessions across github.com and GitHub Enterprise Cloud with Data Residency, with the exception of the U.S. region.

The integration of ML-KEM provides users with a newer, high-performance key exchange alternative designed specifically to remain secure against attacks mounted by quantum computers. Users utilizing standard compliant clients should experience this transition seamlessly, as most updated SSH software will automatically adopt or negotiate the enhanced mechanisms without requiring manual intervention.

Timeline and Enterprise Server Rollout

The transition schedule begins on October 14, 2026, when the new RSA key size requirements take effect and mlkem768x25519-sha256 is enabled. To help administrators and developers identify compatibility issues, GitHub has scheduled brownouts for the removal of the ssh-rsa signature type and the diffie-hellman-group-exchange-sha256 algorithm on November 4, 2026, and again on December 9, 2026. The definitive removal is scheduled for January 13, 2026.

For GitHub Enterprise Server deployments, these modifications will be integrated into version 3.25. The sole exception is the incorporation of the mlkem768x25519-sha256 algorithm, which will arrive slightly earlier in version 3.24.

Impact on Developers and Git Clients

The modifications will specifically impact users connecting via a Git client over SSH or those utilizing the unauthenticated Git protocol on GitHub Enterprise Server. Developers whose Git remotes initiate with HTTPS will remain completely unaffected by the security updates.

Developers currently leveraging existing RSA keys are advised to verify that their systems utilize RSA with SHA-2 options, such as rsa-sha2-256 and rsa-sha2-512 signature types. Users do not need to generate entirely new keys because all RSA keys retain the capability to sign with multiple hash algorithms, provided that the underlying SSH implementation supports RSA with SHA-2.

For those unable to upgrade older software environments, alternative key types such as Ed25519 or ECDSA are recommended, as they remain strong and fully supported. For generating brand new credentials, GitHub recommends using Ed25519 keys where possible, or ensuring that any newly minted RSA keys meet the updated 3072-bit minimum threshold.

Sources

• GitHub ChangelogSecurity improvements for SSH