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SSH Key Fingerprint Changes

cn flag
CRThaze

So I copied an SSH private key from my Linux machine to my M1 Mac. (I've attempted to do this both by uploading the cyphertext to a secrets manager as well as directly transfering the file) but when attempting to SSH to the same machine from each I can only succeed from the Linux machine.

Linux machine:

$ ssh -V
OpenSSH_8.2p1 Ubuntu-4ubuntu0.4, OpenSSL 1.1.1f  31 Mar 2020
$ md5sum id_rsa
7ed8b0c73e168ef48acc715d4c6bcf73  id_rsa
$ sha256sum id_rsa
969d0a35b36c50035881bdd2d8367b90dbff548131d5c72989d29e83b7a3aa19  id_rsa
$ ssh-keygen -l -f id_rsa
4096 SHA256:d19Ee+tlzVHitLzKuuZbdgYcnhla96ypXNtpBwrqfqE [email protected] (RSA)
$ ssh -i id_rsa [email protected]
[redacted MOTD; WORKS]

M1 Mac:

$ ssh -V
openSSH_8.6p1, LibreSSL 2.8.3
$ md5 id_rsa
MD5 (id_rsa) = 7ed8b0c73e168ef48acc715d4c6bcf73
$ shasum -a 256 id_rsa
969d0a35b36c50035881bdd2d8367b90dbff548131d5c72989d29e83b7a3aa19  id_rsa
$ ssh-keygen -l -f id_rsa
4096 SHA256:rWsP9jN2otlchh8icr/jlnZxDjEfEkngDJOoPh4RYZI [email protected] (RSA)
$ ssh -i id_rsa [email protected]
[email protected]: Permission denied (publickey).

AFAICT these private keys are identical. However for some reason ssh-keygen does not fingerprint them thesame. Even though they have identical checksums. Could this be an issue with the M1 SoC? Or is there something much more obvious happening here?

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user1686 avatar
fr flag
user1686
Do the corresponding `id_rsa.pub` files match? Yes, I'm specifically asking about the `.pub` files.
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CRThaze avatar
cn flag
CRThaze
@user1686 that was it! Apparently the -l flag on ssh-keygen causes it to fingerprint the public key even if the path is to the private. And there is where the mismatch was.
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cn flag
CRThaze

The issue here was a misunderstanding with how ssh-keygen reports on figerprints. Even if you provide it with the path to a private key, with the -l flag it will use the corresponding public key file. And that's where I still had a mismatch. Upon fixing the public key everything worked as expected.

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