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which rules I should choose for ssh algo selection, provided it will be used near 100% for git operations? I'm going to use it with git on linux laptops, often used on public wifi.

currently I have:

  1. speed
  2. modern (no need to serve old SSH servers)

and that leads me to Curve25519 selection, but do I miss something important?

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  • I don't think the Git use case matters. Indeed, Curve25519 is very popular nowadays due to providing a similar security level to large RSA keys in a more efficient manner. Not that efficiency is likely to matter for your use case.
    – amon
    Commented Jan 29, 2022 at 10:10
  • @amon thanks for point provided. The git use case had been mentioned to underline that I don't have anything security-challenging (e.g. I have no large data transfers between authority domains with high security and/or privacy demands; nothing periodical, semi-permanent; nothing I should worry about accounting/auditing). That said, shorter keys make it easier to handle clusters of keys per business case or use case.
    – aytvill
    Commented Feb 1, 2022 at 7:47

2 Answers 2

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Typically, I would recommend Ed25519 keys assuming the servers you're using support it. Ed25519 is reasonably well supported among modern SSH clients and servers, and it provides a 128-bit security level, which we presently believe is secure.

Another popular type is RSA keys, but they require a 3072-bit key to provide a 128-bit security level, and unlike Ed25519, which is almost always implemented in a constant-time manner, RSA is slower and may not be constant time in all implementations. Ed25519 also always uses SHA-512, whereas in some case RSA keys can use SHA-1, which is no longer secure.

Mozilla also recommends Ed25519 keys, as does GitHub.

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Based on your use case the i would say the preference is dependent upon which algo and key creation and replacement technology you understand best and are most comfortable using

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