Show the bubblebabble digest of specified private or public key file. Higher numbers result in slower passphrase verification and increased resistance to brute-force password cracking (should the keys be stolen). When saving a private key, this option specifies the number of KDF (key derivation function, currently bcrypt_pbkdf(3)) rounds used. This is used by /etc/rc to generate new host keys. If -f has also been specified, its argument is used as a prefix to the default path for the resulting host key files. This may be used when generating new keys, and existing new-format keys may be converted using this option in conjunction with the -p (change passphrase) flag.Īfter a key is generated, ssh-keygen will ask where the keys should be placed to be activated.įor each of the key types (rsa, dsa, ecdsa and ed25519) for which host keys do not exist, generate the host keys with the default key file path, an empty passphrase, default bits for the key type, and default comment. It is still possible for ssh-keygen to write the previously-used PEM format private keys using the -m flag. The comment is initialized to when the key is created, but can be changed using the -c option. The key comment may be useful to help identify the key. This format is preferred as it offers better protection for keys at rest as well as allowing storage of key comments within the private key file itself. Ssh-keygen will by default write keys in an OpenSSH-specific format. If the passphrase is lost or forgotten, a new key must be generated and the corresponding public key copied to other machines. There is no way to recover a lost passphrase. The passphrase can be changed later by using the -p option. Good passphrases are 10-30 characters long, are not simple sentences or otherwise easily guessable (English prose has only 1-2 bits of entropy per character, and provides very bad passphrases), and contain a mix of upper and lowercase letters, numbers, and non-alphanumeric characters. A passphrase is similar to a password, except it can be a phrase with a series of words, punctuation, numbers, whitespace, or any string of characters you want. The passphrase may be empty to indicate no passphrase (host keys must have an empty passphrase), or it may be a string of arbitrary length. The public key is stored in a file with the same name but “.pub” appended. Normally this program generates the key and asks for a file in which to store the private key. Additionally, the system administrator may use this to generate host keys, as seen in /etc/rc. Normally each user wishing to use SSH with public key authentication runs this once to create the authentication key in ~/.ssh/id_dsa, ~/.ssh/id_ecdsa, ~/.ssh/id_ecdsa_sk, ~/.ssh/id_ed25519, ~/.ssh/id_ed25519_sk or ~/.ssh/id_rsa. See the Key Revocation Lists section for details. See the Moduli Generation section for details.įinally, ssh-keygen can be used to generate and update Key Revocation Lists, and to test whether given keys have been revoked by one. Ssh-keygen is also used to generate groups for use in Diffie-Hellman group exchange (DH-GEX). If invoked without any arguments, ssh-keygen will generate an RSA key. The type of key to be generated is specified with the -t option. ssh-keygen can create keys for use by SSH protocol version 2. Ssh-keygen generates, manages and converts authentication keys for ssh(1). Y verify -f allowed_signers_file -I signer_identity -n namespace -s signature_file Retrieve the fingerprint of a key in MD5 Hex: ssh-keygen -l -E md5 -f ~/.ssh/filenameĬhange the password of a key: ssh-keygen -p -f ~/.ssh/filenameĬhange the type of the key format (for example from OPENSSH format to PEM), the file will be rewritten in-place: ssh-keygen -p -N "" -m PEM -f ~/.ssh/OpenSSH_private_key Remove the keys of a host from the known_hosts file (useful when a known host has a new key): ssh-keygen -R remote_host Generate an RSA 4096-bit key with email as a comment: ssh-keygen -t dsa|ecdsa|ed25519|rsa -b 4096 -C " comment|email" Generate an ed25519 key with 100 key derivation function rounds: ssh-keygen -t ed25519 -a 100 Specify file in which to save the key: ssh-keygen -f ~/.ssh/filename OpenSSH authentication key utility Examples (TL DR)
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