ssh-keygen allows generation of new key pair for authentication (SSH).
> ssh-keygen --help unknown option -- - usage: ssh-keygen [-q] [-b bits] [-t dsa | ecdsa | ed25519 | rsa | rsa1] [-N new_passphrase] [-C comment] [-f output_keyfile] ssh-keygen -p [-P old_passphrase] [-N new_passphrase] [-f keyfile] ssh-keygen -i [-m key_format] [-f input_keyfile] ssh-keygen -e [-m key_format] [-f input_keyfile] ssh-keygen -y [-f input_keyfile] ssh-keygen -c [-P passphrase] [-C comment] [-f keyfile] ssh-keygen -l [-v] [-E fingerprint_hash] [-f input_keyfile] ssh-keygen -B [-f input_keyfile] ssh-keygen -D pkcs11 ssh-keygen -F hostname [-f known_hosts_file] [-l] ssh-keygen -H [-f known_hosts_file] ssh-keygen -R hostname [-f known_hosts_file] ssh-keygen -r hostname [-f input_keyfile] [-g] ssh-keygen -G output_file [-v] [-b bits] [-M memory] [-S start_point] ssh-keygen -T output_file -f input_file [-v] [-a rounds] [-J num_lines] [-j start_line] [-K checkpt] [-W generator] ssh-keygen -s ca_key -I certificate_identity [-h] [-n principals] [-O option] [-V validity_interval] [-z serial_number] file ... ssh-keygen -L [-f input_keyfile] ssh-keygen -A ssh-keygen -k -f krl_file [-u] [-s ca_public] [-z version_number] file ... ssh-keygen -Q -f krl_file file ...
ssh-keygen -t rsa Generating public/private rsa key pair. Enter file in which to save the key (/root/.ssh/id_rsa): Enter passphrase (empty for no passphrase): Enter same passphrase again: Your identification has been saved in /root/.ssh/id_rsa. Your public key has been saved in /root/.ssh/id_rsa.pub. The key fingerprint is: SHA256:KjqBCXEEFIBOOPDJ6j45tOBogwggxw3pAqECLG/r9fI firstname.lastname@example.org The key's randomart image is: +---[RSA 2048]----+ |%* . | |%==. | |O*+o | |*o* . | |=* . S | |*.o . . | |Oooo... | |=Oo.... | |..=. oE | +----[SHA256]-----+
– The SSH protocol uses public key cryptography for authenticating hosts and users.
– SSH keys are authentication credentials just like passwords.
ssh-copy-id allows copying/installation of public key to a server to allow public key authentication.
> ssh-copy-id -h Usage: /usr/bin/ssh-copy-id [-h|-?|-f|-n] [-i [identity_file]] [-p port] [[-o <ssh -o options>] ...] [user@]hostname -f: force mode -- copy keys without trying to check if they are already installed -n: dry run -- no keys are actually copied -h|-?: print this help
> ssh-copy-id email@example.com /usr/bin/ssh-copy-id: INFO: Source of key(s) to be installed: "/root/.ssh/id_rsa.pub" /usr/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed /usr/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now it is to install the new keys firstname.lastname@example.org's password: Number of key(s) added: 1 Now try logging into the machine, with: "ssh 'email@example.com'" and check to make sure that only the key(s) you wanted were added.