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In a public key file "id_rsa.pub" generated by ssh-keygen, does the part after the == matter?

I ask because when I changed "[email protected]" to "root", it seems to still work.

More generally, I am curious about what the purpose of that half is.

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This right part of a public key (either "id_rsa.pub" or "id_dsa.pub") is just a comment and is usually filled with the < login>@< hostname> who generated the key. This in a way similar to the comment field from the SSH Public Key File Format (see RFC 4716).

So, as being purely informational and optional, you can change it to whatever you like, but keeping the < login>@< hostname> is a practical way to keep track of what is what.

For more about OpenSSH "authorized_keys" format:

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  • Is there an RFC or similar document for this format as well? I've seen other funny things in these authorized_keys files as well, such as actual commands.
    – merlin2011
    Commented Dec 9, 2012 at 9:53
  • 2
    This format seems openssh specific... but one of the most widely used. You can find some info about it in the openssh sshd manpage, in the "AUTHORIZED_KEYS FILE FORMAT" section.
    – Ouki
    Commented Dec 9, 2012 at 10:02
  • The openssh sshd manpage is now at http://www.freebsd.org/cgi/man.cgi?sshd(8)
    – Chirael
    Commented Jul 1, 2016 at 17:11
  • OpenSSH reference should be OpenBSD, not FreeBSD. Here is the right man page: openssh sshd manpage
    – Ouki
    Commented Jul 1, 2016 at 19:49
  • in Google Cloud Platform, they implemented it in a way that the right part must be the username
    – Jossef Harush Kadouri
    Commented Jul 11, 2019 at 12:52

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