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I've been running with ssh-rsa disabled for a while (with a config based on https://infosec.mozilla.org/guidelines/openssh#modern-openssh-67 https://infosec.moz

I've been running with ssh-rsa disabled for a while (with a config based on https://infosec.mozilla.org/guidelines/openssh#modern-openssh-67 https://infosec.mozilla.org/guidelines/openssh#modern-openss... ) and it's been pretty smooth. Support for better algorithms is widespread, with a few exceptions (like bazaar.launchpad.net). One gotcha: OpenWrt does not enable ECDSA by default[1] and only recently enabled support for ed25519 by default.[2][3] It's available in release candidates for 21.02, but not in current stable releases. So if you're running a stable release you'll need to either add `PubkeyAcceptedKeyTypes +ssh-rsa` to your client ssh_config or use a custom build of OpenWrt with DROPBEAR_ECC or DROPBEAR_ECC_FULL enabled. [1]: https://bugs.openwrt.org/index.php?do=details&task_id=786 https://bugs.openwrt.org/index.php?do=details&task_id=786 [2]: https://git.openwrt.org/?p=openwrt/openwrt.git;a=commit;h=d0f295837a03f7f52000ae6d395827bdde7996a4 https://git.openwrt.org/?p=openwrt/openwrt.git;a=commit;h=d0... [3]: https://bugs.openwrt.org/index.php?do=details&task_id=3216&string=dropbear https://bugs.openwrt.org/index.php?do=details&task_id=3216&s... [4]: https://bugs.openwrt.org/index.php?do=details&task_id=3452 https://bugs.openwrt.org/index.php?do=details&task_id=3452

wahern 5y ago
OpenSSH that ships with macOS doesn't support ECC keys loaded via PKCS#11, only RSA keys. This is the case even on Big Sur because though it ships OpenSSH 8.1p1 its linked against LibreSSL 2.7.3, which lacks support for delegating non-RSA signing operations. This is annoying if you're using an HSM or secure enclave via PKCS#11; for example the T2, which only supports ECDSA P-256. There's nothing wrong with RSA keys. What's being disabled is the use of SHA-1 for signature hashing. SHA-2 works just fine and the same RSA keys continue working.
- kevinoid 5y ago
  Agreed. I should have made my post clearer. OpenWrt does not suppport SHA-2 signature hashing or any of the newer key algorithms I mentioned, so you are stuck with RSA+SHA1.

wahern 5y ago

OpenSSH that ships with macOS doesn't support ECC keys loaded via PKCS#11, only RSA keys. This is the case even on Big Sur because though it ships OpenSSH 8.1p1 its linked against LibreSSL 2.7.3, which lacks support for delegating non-RSA signing operations. This is annoying if you're using an HSM or secure enclave via PKCS#11; for example the T2, which only supports ECDSA P-256. There's nothing wrong with RSA keys. What's being disabled is the use of SHA-1 for signature hashing. SHA-2 works just fine and the same RSA keys continue working.

kevinoid 5y ago
Agreed. I should have made my post clearer. OpenWrt does not suppport SHA-2 signature hashing or any of the newer key algorithms I mentioned, so you are stuck with RSA+SHA1.