SSH connection with public key

Connect with a public key rather than a User/Password represents several advantages:

a generated key will always be more robust than a password in general
there is no need to use a password to connect to SSH

Generation of the key

Choose the key type according to the server capabilities. Ed25519 is recommended on modern systems, while RSA 4096 remains useful for compatibility with older servers.

ssh-keygen -t ed25519

ssh-keygen -t rsa -b 4096

Tip

Avoid DSA, which is obsolete. Protect the private key with a passphrase as well.

GENERATING PUBLIC/PRIVATE ED25519 KEY PAIR.
Enter File in Which to Save the Key (/home/contact/.ssh/id_ed25519):
Created Directory '/home/Contact/.ssh'.
Enter Passphrase (Empty for No Passphrase):
Enter SADS PASSPHRASE Again:
Your identification has been saved in /home/contact/.ssh/id_ed25519
Your public Key has been saved in /home/contact/.ssh/id_ed25519.pub
The Key Fingerprint is:
Sha256: Monhash Contact@Mondomain
The Key's Randomart Image is:
+-[Ed25519 256]-+
|%@+.|
| EBCVB.|
|+= BO.|
|+.O*.|
| oo..o.S S |
| =+oo o |
| B ++ o..|
|+= .. o.|
| o...|
+---- [SHA256] -----+

Inform connection information

ssh-copy-id contact@mydomain

ssh-copy-id Nom_user@ip_ou_domaine

/usr/bin/ssh-copy -id: info: source of key (s) to be installed: "/root/.ssh/id_rsa.pub"
The Authenticity of Host 'DNS.it.fr (172.16.10.10)' Can't Be Established.
ECDSA Key FingerPrint is sha256: LDA9PSN+R3COE3P2EH2HDAR6F50GATNLUTF5HW+QQKA.
Are you sure you want to continue connecting (Yes/No/[Fingerprint])?Yes
/usr/bin/ssh-copy-Iid: info: attempting to log in with the new key (s), to filter out any that are alreni installedy
/usr/bin/ssh-copy-ID: info: 1 key (s) remain to be installed-if you are prompt now it is to install the keys
admin@dns.it.fr's password:

Number of Key (s) Added: 1

Now Try Logging Into the Machine, with: "ssh 'admin@dns.it.fr'"
and check to make sure that only the key (s) you wanted were added.

Connect to SSH

ssh admin@dns.it.fr

ssh nom_user@ip_ou_domaine

Tip

You are now connected in Shh thanks to the authorization key.

Export the authorization key

cat .ssh/authorized_keys

SSH-RSA AAAAB3NZAC1C2EAAAADAQABAABGQC/3HQOJNQS9OCUAKIFAMOB4TWLZFSGF50VAO7H7AT3
FIMZ+HQEKTTMDS8CXOJAHA1J+4Z4+2HFHBVO5EXL4/HMYZTMBJZVEIMAK+J5UXNRZX6EBVL6BTZG7W
EK5IFRRTBLVIDGKQRI4E1DV8C7NUPDQBAGTIS3+UW3MIWKKNY6HVGJ6TIQT1ELRI38CVUX26PCUG
6FBVHQXOXTBWLOJUXZYD2NAYH4ZLVYR34KTPYCNKAOVFAYRSNBVCQ3A7XQWLUURPYOAJTNDWCBUI4EKO
ISTFQVGC7BT9SCPMYYKLB+D58QOWL74VELOQIRUDGC0O66ZX3BCTKU6DW9AGI/LWDODJLQHQQDIHKDIHKDIHKDIHKDIHK
G15VIGNCNTCY4F9P+KCG3G2TP+KNXMMBTUWll8mma6odLGLFTPAXJXJS+L9CPEOUWT2SKGHGXPUXFL
Lmtnqfsjmtbzhh5ywb0eq8fyvnbisj02t0jd8goq6qcia+7rwou15vu+hip5qrcu17cejze = root@
PC-Admin