GitHub sets stronger SSH requirements and adds post-quantum key exchange support

GitHub has published a set of SSH security changes that will affect developers, CI systems, and enterprise tooling that still rely on older SSH algorithms. The company says it is removing RSA signatures that use SHA-1, retiring the diffie-hellman-group-exchange-sha256 key exchange method, requiring stronger new RSA keys, and adding a post-quantum key exchange option for many GitHub SSH sessions.

The first operational date is October 14, 2026. From that point, new RSA SSH keys uploaded to GitHub must be at least 3072 bits for signing and authentication. GitHub also plans to enable mlkem768x25519-sha256 on github.com and GitHub Enterprise Cloud with Data Residency, except in the United States region. The company says the algorithm gives SSH sessions a newer key exchange method intended to remain secure against quantum computers.

Who needs to check systems now

GitHub says users whose remotes start with https are not affected. The practical audience is anyone using Git over SSH, plus teams with unauthenticated Git protocol usage on GitHub Enterprise Server. That includes developer laptops, build runners, release automation, deployment scripts, and older Java or SSH libraries embedded inside internal tools.

The important distinction is that existing RSA keys do not automatically need to be replaced. GitHub says RSA keys can keep working if the SSH client supports SHA-2 signatures through rsa-sha2-256 or rsa-sha2-512. The risk sits with older clients and libraries that still negotiate the SHA-1 ssh-rsa signature type or the retiring Diffie-Hellman exchange.

• OpenSSH needs version 7.2p1 or newer for robust default RSA SHA-2 support.
• TeamCity needs version 2021.2.3 or newer.
• Go SSH needs version 0.16.0 or newer.
• libssh2 needs version 1.11.0 or newer.
• PuTTY needs version 0.82 or newer.

The CyberOGZ read

This is a maintenance story with real production risk. The safest response is not a rushed key rotation across every account. Teams should first inventory SSH clients in CI, developer images, deployment hosts, and vendor integrations, then test whether those clients already negotiate SHA-2 signatures. Ed25519 is the cleaner default for new GitHub keys when compatibility allows it, while 3072-bit RSA remains the fallback for services that still require RSA.

The post-quantum addition is also notable because users should not have to change anything when their clients can prefer the new exchange. The bigger near-term value is the deadline. Organizations that treat SSH as invisible plumbing have a window to find old build agents before the brownout period turns a forgotten library into a failed release.

Sources

• github.blog

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