secsh-keygen, ssh-keygen -- authentication key generation, management and conversion

SYNOPSIS

secsh-keygen [-qv] [-b bits] [-t type] [-N new_passphrase] [-C comment] [-f output_keyfile]

secsh-keygen -p [-v] [-P old_passphrase] [-N new_passphrase] [-f keyfile]

secsh-keygen -i [-v] [-f input_keyfile]

secsh-keygen -e [-v] [-f input_keyfile]

secsh-keygen -y [-v] [-f input_keyfile]

secsh-keygen -c [-v] [-P passphrase] [-C comment] [-f keyfile]

secsh-keygen -l [-v] [-f input_keyfile]

secsh-keygen -B [-v] [-f input_keyfile]

secsh-keygen -D reader [-v]

secsh-keygen -U reader [-v] [-f input_keyfile]

secsh-keygen -G reader -t type [-qv] [-b bits] [-f input_keyfile]

secsh-keygen -F hostname [-f known_hosts_file] [-l]

secsh-keygen -H [-f known_hosts_file]

secsh-keygen -R hostname [-f known_hosts_file]

secsh-keygen -r hostname [-f input_keyfile] [-q]

ssh-keygen [-qv] [-b bits] [-t type] [-N new_passphrase] [-C comment] [-f output_keyfile]

ssh-keygen -p [-v] [-P old_passphrase] [-N new_passphrase] [-f keyfile]

ssh-keygen -i [-v] [-f input_keyfile]

ssh-keygen -e [-v] [-f input_keyfile]

ssh-keygen -y [-v] [-f input_keyfile]

ssh-keygen -c [-v] [-P passphrase] [-C comment] [-f keyfile]

ssh-keygen -l [-v] [-f input_keyfile]

ssh-keygen -B [-v] [-f input_keyfile]

ssh-keygen -D reader [-v]

ssh-keygen -U reader [-v] [-f input_keyfile]

ssh-keygen -G reader -t type [-qv] [-b bits] [-f input_keyfile]

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] [-q]

secsh-keygen generates, manages and converts authentication keys for secsh. secsh-keygen can generate a RSA1 key for use by SSH protocol version 1 as well as RSA or DSA keys for use by SSH protocol version 2. The type of key to be generated is specified with the -t option.

Normally each user wishing to use SSH with RSA or DSA authentication runs this once to create the authentication key in $USERPROFILE/.ssh/identity, $USERPROFILE/.ssh/id_dsa, or $USERPROFILE/.ssh/id_rsa. At the time of installation, the installer will also use this tool to generate host keys.

Normally, this program generates the key and asks for a file in which to store the private key. The public key is stored in a file with the same name but with .pub appended. The program also asks for a passphrase. 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. Good passphrases are 10-30 characters long and are not simple sentences or otherwise easily guessable (English prose has only 1-2 bits of entropy per character, and provides very bad passphrases). The passphrase can be changed later by using the -p option.

There is no way to recover a lost passphrase. If the passphrase is lost or forgotten, a new key must be generated and copied to the corresponding public key to other machines.

For RSA1 keys, there is also a comment field in the key file that is only for convenience to the user to help identify the key. The comment can tell what the key is for, or whatever is useful. The comment is initialized to user@host when the key is created, but can be changed using the -c option.

After a key is generated, instructions below detail where the keys should be placed to be activated.

You can also call secsh-keygen as ssh-keygen.

Options

-B: Shows the bubblebabble digest of specified private or public key file.
-b bits: Specifies the number of bits in the key to create. For RSA keys, the minimum is 768 bits and the default is 2048 bits. Generally 2048 bits is considered sufficient. DSA keys must be exactly 1024 bits as specified by FIPS 186-2.
-C: Provides the new comment.
-c: Requests changing the comment in the private and public key files. This operation is only supported for RSA1 keys. The program will prompt for the file containing the private keys, for passphrase if the key has one, and for the new comment.
-D reader: Downloads the RSA public key stored in the smartcard in reader.
-e: Reads a private or public OpenSSH key file and writes the key in RFC 4716 SSH Public Key File Format to the standard output. This option allows exporting keys for use by several commercial SSH implementations.
-F hostname: Searches for the specified hostname in a known_hosts file, listing any occurrences found. This option is useful to find hashed host names or addresses and may also be used in conjunction with the -H option to print found keys in a hashed format.
-f filename: Specifies the file name of the key file.
-G reader: Uses the smartcard in the specified reader to generate a keypair. In this instance, secsh-keygen only creates a disk file for the public key in the keypair, as it is not possible to download private keys from a smartcard.
-g: Uses generic DNS format when printing fingerprint resource records using the -r command.
-H: Hashes a known_hosts file. This replaces all hostnames and addresses with hashed representations within the specified file; the original content is moved to a file with a .old suffix. These hashes may be used normally by secsh and secshd, but they do not reveal identifying information should the file's contents be disclosed. This option does not modify existing hashed hostnames and is therefore safe to use on files that mix hashed and non-hashed names.
-i: Reads an unencrypted private (or public) key file in SSH2-compatible format and writes an OpenSSH compatible private (or public) key to the standard output. secsh-keygen also reads the RFC 4716 SSH Public Key File Format. This option allows importing keys from several commercial SSH implementations.
-l: Shows fingerprint of specified private or public key file. Private RSA1 keys are also supported. For RSA and DSA keys, ssh-keygen tries to find the matching public key file and prints its fingerprint. When combined with -v, an ASCII art representation of the key is supplied with the fingerprint.
-N new_passphrase: Provides the new passphrase.
-P passphrase: Provides the (old) passphrase.
-p: Requests changing the passphrase of a private key file instead of creating a new private key. The program will prompt for the file containing the private key, for the old passphrase, and twice for the new passphrase.
-q: Silences secsh-keygen.
-R hostname: Removes all keys belonging to hostname from a know_hosts file. This option is useful to delete hashed hosts (see the -H above).
-r hostname: Prints the SSHFP fingerprint resource record named hostname for the specified public key file.
-t type: Specifies the type of the key to create. The possible values are rsa1 for protocol version 1 and rsa or dsa for protocol version 2.
-U reader: Upload an existing RSA private key into the smartcard in reader.
-v: Causes secsh-keygen to display debugging messages about its progress. This is helpful in debugging smartcard and key generation problems. Specifying multiple -v options (to a maximum of three) increases the verbosity.
-y: Reads a private OpenSSH format file and prints an OpenSSH public key to stdout.

FILES

$USERPROFILE/.ssh/identity: Contains the protocol version 1 RSA authentication identity of the user. This file should not be readable by anyone but the user. It is possible to specify a passphrase when generating the key; that passphrase will be used to encrypt the private part of this file using 3DES. This file is not automatically accessed by secsh-keygen but it is offered as the default file for the private key. secsh will read this file when a login attempt is made.
$USERPROFILE/.ssh/identity.pub: Contains the protocol version 1 RSA public key for authentication. The contents of this file should be added to ~/.ssh/authorized_keys on all machines where the user wishes to log in using RSA authentication. There is no need to keep the contents of this file secret.
$USERPROFILE/.ssh/id_dsa: Contains the protocol version 2 DSA authentication identity of the user. This file should not be readable by anyone but the user. It is possible to specify a passphrase when generating the key; that passphrase will be used to encrypt the private part of this file using 3DES. This file is not automatically accessed by secsh-keygen but it is offered as the default file for the private key. secsh will read this file when a login attempt is made.
$USERPROFILE/.ssh/id_dsa.pub: Contains the protocol version 2 DSA public key for authentication. The contents of this file should be added to ~/.ssh/authorized_keys2 on all machines where the user wishes to log in using public key authentication. There is no need to keep the contents of this file secret.
$USERPROFILE/.ssh/id_rsa: Contains the protocol version 2 RSA authentication identity of the user. This file should not be readable by anyone but the user. It is possible to specify a passphrase when generating the key; that passphrase will be used to encrypt the private part of this file using 3DES. This file is not automatically accessed by secsh-keygen but it is offered as the default file for the private key. secsh will read this file when a login attempt is made.
$USERPROFILE/.ssh/id_rsa.pub: Contains the protocol version 2 RSA public key for authentication. The contents of this file should be added to ~/.ssh/authorized_keys2 on all machines where the user wishes to log in using public key authentication. There is no need to keep the contents of this file secret.

AUTHORS

OpenSSH is a derivative of the original and free ssh 1.2.12 release by Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo de Raadt and Dug Song removed many bugs, re-added newer features and created OpenSSH. Markus Friedl contributed the support for SSH protocol versions 1.5 and 2.0.

PORTABILITY

All UNIX systems. Windows 2000. Windows XP. Windows Server 2003. Windows Vista. Windows 7. Windows Server 2008.

NOTES

Typically, the $USERPROFILE directory in a Windows domain environment is local to the machine, but is automatically replicated to a server (typically to ~/username.profile) when the user logs in and out, and when roaming profiles are in use. This might not be a desirable location to store private keys from a key management and security point of view.

The secsh-keygen utility, by default, stores key files under the $USERPROFILE directory on Windows NT/2000/XP/2003/Vista/7/2008 platforms instead of ~/. This was done because the ~/ directory might not be available for the case of a domain machine that cannot contact a domain controller. Note that the secure shell service continues to use the ~/.ssh directory to store configuration files.

AVAILABILITY

MKS Toolkit for System Administrators
MKS Toolkit for Developers
MKS Toolkit for Interoperability
MKS Toolkit for Professional Developers
MKS Toolkit for Enterprise Developers
MKS Toolkit for Enterprise Developers 64-Bit Edition

secsh-keygen, ssh-keygen
authentication key generation, management and conversion

Command