GitHub set 14 October 2026 as the date new SSH RSA keys must be at least 3,072 bits, and starts brownouts in November for SSH clients still using SHA-1

Every RSA SSH key that reaches GitHub after 14 October 2026 has to be at least 3,072 bits, and every SSH client still relying on the SHA-1 signature type loses access on 13 January 2027. GitHub published the timeline on 22 September 2026, along with a new post-quantum key-exchange algorithm on github.com and GitHub Enterprise Cloud with Data Residency.

What is going away, and when

GitHub says the ssh-rsa signature type, which uses SHA-1, is being removed. The company writes that "any client that still uses ssh-rsa will fail to authenticate". The two other removals are diffie-hellman-group-exchange-sha256, which GitHub describes as "a slow, little-used algorithm", and RSA keys shorter than 3,072 bits for new uploads.

The dates are fixed. On 14 October 2026 the 3,072-bit minimum takes effect for new keys. On 4 November GitHub runs a first brownout: any client still using ssh-rsa or the older Diffie-Hellman algorithm is refused during the window and can reconnect after it. A second brownout runs on 9 December. Final removal is 13 January 2027. GitHub says existing RSA keys shorter than 3,072 bits keep working during this period, but they cannot be re-uploaded once removed.

The new post-quantum algorithm is already on

Alongside the removals, GitHub turned on mlkem768x25519-sha256, a key exchange based on ML-KEM 768 combined with X25519. GitHub says the algorithm is "secure against quantum computers" and is available on github.com and GitHub Enterprise Cloud with Data Residency, but not in the U.S. region on Data Residency. A recent OpenSSH client picks the new algorithm without any configuration change.

What to check on each machine

GitHub recommends rsa-sha2-256 and rsa-sha2-512 as the RSA replacements, and points readers to Ed25519 keys, which the company says "are strong, secure, and will continue to work for the indefinite future". The machines most likely to fail are old CI runner images, build agents baked in 2020, embedded devices that reach GitHub for firmware pulls, and vendored SSH libraries pinned by a repository that has not been touched in years. A modern developer laptop usually runs a current OpenSSH and is fine. The verify step on any of them is ssh -vT git@github.com, reading the signature type back from the debug output.

For a team building software, the deadline changes what a security audit reads for. The list of machines that push to GitHub has to be checked once against the signature type each of them negotiates, and any that still say ssh-rsa need a new key on a modern client before January. The 4 November brownout is the free test: any machine that loses access that day is on the list of things to fix, and every other machine is fine.

Source

GitHub Changelog, Security improvements for SSH, 22 September 2026.