Bash - print fingerprints for SSHD keys (md5, sha-1, sha-A256 fingerprints)

In this short article, we would like to show how using Bash, get a fingerprints for certificates used by SSH server under Debian.

Simple steps:

1. login to your server,
    
2. list keys in /etc/ssh directory with the following command:
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   xxxxxxxxxx

    

   1

   ls -al /etc/ssh

   Example output:

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   1

   total 600

   2

   drwxr-xr-x  2 root root   4096 Jun 19 17:22 .

   3

   drwxr-xr-x 79 root root   4096 Sep 15 08:44 ..

   4

   -rw-r--r--  1 root root 565189 Jan 31  2020 moduli

   5

   -rw-r--r--  1 root root   1580 Jan 31  2020 ssh_config

   6

   -rw-r--r--  1 root root   3233 May 29 13:40 sshd_config

   7

   -rw-------  1 root root   1381 May 29 12:05 ssh_host_dsa_key

   8

   -rw-r--r--  1 root root    607 May 29 12:05 ssh_host_dsa_key.pub

   9

   -rw-------  1 root root    513 May 29 12:05 ssh_host_ecdsa_key

   10

   -rw-r--r--  1 root root    179 May 29 12:05 ssh_host_ecdsa_key.pub

   11

   -rw-------  1 root root    411 May 29 12:05 ssh_host_ed25519_key

   12

   -rw-r--r--  1 root root     99 May 29 12:05 ssh_host_ed25519_key.pub

   13

   -rw-------  1 root root   1823 May 29 12:05 ssh_host_rsa_key

   14

   -rw-r--r--  1 root root    399 May 29 12:05 ssh_host_rsa_key.pub
    
3. select one key and print fingerprints with the following commands:
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   1

   ssh-keygen -l -E md5 -f /etc/ssh/ssh_host_rsa_key.pub

   2

   ssh-keygen -l -E sha1 -f /etc/ssh/ssh_host_rsa_key.pub

   3

   ssh-keygen -l -E sha256 -f /etc/ssh/ssh_host_rsa_key.pub

   Where: rsa in ssh_host_rsa_key.pub in the above command can be replaced by dsa, ecdsa or ed25519 depending on available cryptographic algorithms.

   Example output:

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   1

   2048 MD5:9a:f3:d8:2a:fa:54:80:46:1b:63:52:7d:2f:37:f8:b5 root@my-server (RSA)

   2

   2048 SHA1:X0NYsrgjgSINFEZkWuNOogbImPP root@my-server (RSA)

   3

   2048 SHA256:iJcZp8p1XlTJFpsQfDb5fEwGzt2vPsshm43hi+tQU2V root@my-server (RSA)

Hint: in the presented results, /etc/ssh/ssh_host_rsa_key.pub file contained only one key.

1. SSH - verify used local and server key fingerprints (Windows - Linux connection verification)