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OpenSSH keygen guidelines

Posted by jpluimers on 2020/05/01

Verify [WayBack] OpenSSH: Key generation before generating keys.

At the time of grabbing it was this (for the mozilla tag; use another tag if you prefer):

# RSA keys are favored over ECDSA keys when backward compatibility ''is required'',
# thus, newly generated keys are always either ED25519 or RSA (NOT ECDSA or DSA).
$ ssh-keygen -t rsa -b 4096 -f ~/.ssh/id_rsa_mozilla_$(date +%Y-%m-%d) -C "Mozilla key for xyz"

# ED25519 keys are favored over RSA keys when backward compatibility ''is not required''.
# This is only compatible with OpenSSH 6.5+ and fixed-size (256 bytes).
$ ssh-keygen -t ed25519 -f ~/.ssh/id_ed25519_mozilla_$(date +%Y-%m-%d) -C "Mozilla key for xyz"

This was not changed based on [WayBack] Key generation: pass-a and -o argument? · Issue #68 · mozilla/wikimo_content · GitHub: a discussion on the KDF rounds (-a parameter) and storage format (-o parameter).

This is slightly less strong than in [WayBack] Upgrade Your SSH Key to Ed25519 | Programming Journal, but seems to be OK when writing this in 2018.

For comparison, a similar discussion is at [WayBack] public key – How many KDF rounds for an SSH key? – Cryptography Stack Exchange.

In practice, I am not for one ssh ID per host, but I use different tags depending on where the ssh ID applies. More discussion on this is at [WayBack] privacy – Best Practice: ”separate ssh-key per host and user“ vs. ”one ssh-key for all hosts“ – Information Security Stack Exchange

Based on the above, I also learned about this password generator: [WayBack] GitHub – gdestuynder/pwgen

–jeroen

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