ssh how to verify your host key / avoid MIM attacks

SSH helps keep us secure in many ways, one of those is the host-key fingerprint which is unique.  If you have been connecting to an SSH server that you've made no changes to and suddenly ssh warns that the key doesn't match then you have a problem.

But how about connecting to an existing server for the first time on a new machine or client?

A lot of new clients calculate it using an SHA256 hash but it is not as easy on your host machine to produce the same style hash without some hacking around.

The authenticity of host 'somehow (172.16.5.2)' can't be established.
RSA key fingerprint is SHA256:alalalalleieieieieiala.
Are you sure you want to continue connecting (yes/no)?

So we can get the MD5 hash by using this option:

ssh -o fingerprinthash=md5 user@host
The authenticity of host 'somehow (172.16.5.2)' can't be established.
RSA key fingerprint is MD5:aa:sldka;:ksdkjd::kala:kfdkls:1.
Are you sure you want to continue connecting (yes/no)?

 

How do we get the md5 hash on our host?

ssh-keygen -l -f /etc/ssh/ssh_host_key.pub
aa:sldka;:ksdkjd::kala:kfdkls:1 /etc/ssh/ssh_host_key.pub (RSA1)

 

On newer versions you will need to do it like this:

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


Tags:

ssh, verify, mim, attacksssh, fingerprint, connecting, server, ve, warns, doesn, existing, calculate, sha, hash, hacking, authenticity, established, rsa, alalalalleieieieieiala, md, fingerprinthash, user, aa, sldka, ksdkjd, kala, kfdkls, keygen, etc, ssh_host_key, pub, newer, versions,

Latest Articles

  • Ubuntu Debian Linux Cannot Install Wine Solution - wine1.6 : Depends: wine1.6-i386 (= 1:1.6.2-0ubuntu14.2) but it is not installable wine1.4 : Depends: wine1.6 but it is not going to be installed
  • How To Install python 3.4 3.5 and up on Linux with wine - Working Solution
  • using Xvfb on virtual remote ssh server to have X graphical programs work
  • ssh Received disconnect from port 22:2: Too many authentication failures
  • named bind errors - DNSKEY: unable to find a DNSKEY which verifies the DNSKEY RRset and also matches a trusted key for '.'
  • OpenVZ vs LXC DIR mode poor security in LXC
  • httpd: Syntax error on line 221 of /etc/httpd/conf/httpd.conf: Syntax error on line 6 of /etc/httpd/conf.d/php.conf: Cannot load modules/libphp5.so into server: /lib64/libresolv.so.2: symbol __h_errno, version GLIBC_PRIVATE not defined in file libc.s
  • Radeon R3 GPU on Debian Crashing
  • MySQL 5.7 on Debian and Ubuntu - How To Reset Root Password
  • SSH and sshfs timeout settings keepalive
  • Linux How To Add User To Additional Group
  • Howto Set Static IP on boot in initramfs for dropbear or other purposes NFS, Linux, Debian, Ubuntu, CentOS
  • Convert and install to LUKS Encrypted Drive Ubuntu 18.04 19.10 Linux Mint and Debian Based Linux
  • Debian and Netplan
  • CentOS 8 how to restart the network!
  • CentOS 8 how to convert to a bootable mdadm RAID software array
  • ADATA USB Thumb Drive Issues
  • KMODE EXCEPTION NOT HANDLED - QEMU/KVM Won't Boot Windows 2016 or 10 Image or Physical Machine
  • Linux Mint / Ubuntu / Debian Mate Disable Guest Session and Hide Usernames on Lightdm Login screen GUI
  • SSH How To Create Public/Private Key Pair and with a Larger Keysize than 2048 bits