NAME
ssh-keygen - authentication key generation, management and conversion
SYNOPSIS
ssh-keygen [-q? [-b bits? [-t type? [-N new_passphrase? [-C comment? [-f output_keyfile?
ssh-keygen -p [-P old_passphrase? [-N new_passphrase? [-f keyfile?
ssh-keygen -i [-f input_keyfile?
ssh-keygen -e [-f input_keyfile?
ssh-keygen -y [-f input_keyfile?
ssh-keygen -c [-P passphrase? [-C comment? [-f keyfile?
ssh-keygen -l [-f input_keyfile?
ssh-keygen -B [-f input_keyfile?
ssh-keygen -D reader
ssh-keygen -U reader [-f input_keyfile?
DESCRIPTION
ssh-keygen generates, manages and converts authentication keys for ssh(1). ssh-keygen defaults to generating a RSA1 key for use by SSH protocol version 1. Specifying the
version 2.
Normally each user wishing to use SSH with RSA or DSA authentication runs this once to create the authentication key in $HOME/.ssh/identity, $HOME/.ssh/id_dsa or $HOME/.ssh/id_rsa. Additionally, the system administrator may use this to generate host keys, as seen in /etc/rc.
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 ``.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.
The options are as follows:
Specifies the number of bits in the key to create.Minimum is 512 bits. Generally 1024 bits is consid-ered sufficient, and key sizes above that no longer improve security but make things slower. The defaultis 1024 bits.
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 the passphrase if the key has one, and for the new comment.
This option will read a private or public OpenSSH keyfile and print the key in a SECSH Public Key !FileFormat to stdout. This option allows exporting keys for use by several commercial SSH implementations.
Specifies the filename of the key file.
This option will read an unencrypted private (or public) key file in SSH2-compatible format and print an OpenSSH compatible private (or public) key to stdout. ssh-keygen also reads the SECSH Public Key !FileFormat. This option allows importing keys from several commercial SSH implementations.
Show fingerprint of specified public key file. Private RSA1 keys are also supported. For RSA and DSA keys ssh-keygen tries to find the matching public keyfile and prints its fingerprint.
Requests changing the passphrase of a private keyfile instead of creating a new private key. The program will prompt for the file containing the privatekey, for the old passphrase, and twice for the newpassphrase.
Silence ssh-keygen. Used by /etc/rc when creating a new key.
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. The default is ``rsa1.
This option will read a private OpenSSH format file and print an OpenSSH public key to stdout.
Show the bubblebabble digest of specified private or public key file.
Provides the new comment.
Download the RSA public key stored in the smartcard in reader.
Provides the new passphrase.
Provides the (old) passphrase.
Upload an existing RSA private key into the smartcard in reader.
FILES
$HOME/.ssh/identity
Contains the protocol version 1 RSA authentication identity of the user. This file should not be read- able by anyone but the user. It is possible to spec- ify 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 automati- cally accessed by ssh-keygen but it is offered as the default file for the private key. ssh(1) will read this file when a login attempt is made.
$HOME/.ssh/identity.pub Contains the protocol version 1 RSA public key for authentication. The contents of this file should be added to $HOME/.ssh/authorized_keys on all machines where the user wishes to log in using RSA authentica- tion. There is no need to keep the contents of this file secret.
$HOME/.ssh/id_dsa Contains the protocol version 2 DSA authentication identity of the user. This file should not be read- able by anyone but the user. It is possible to spec- ify 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 automati- cally accessed by ssh-keygen but it is offered as the default file for the private key. ssh(1) will read this file when a login attempt is made.
$HOME/.ssh/id_dsa.pub Contains the protocol version 2 DSA public key for authentication. The contents of this file should be added to $HOME/.ssh/authorized_keys on all machines where the user wishes to log in using public key authentication. There is no need to keep the con- tents of this file secret.
$HOME/.ssh/id_rsa Contains the protocol version 2 RSA authentication identity of the user. This file should not be read- able by anyone but the user. It is possible to spec- ify 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 automati- cally accessed by ssh-keygen but it is offered as the default file for the private key. ssh(1) will read this file when a login attempt is made.
$HOME/.ssh/id_rsa.pub Contains the protocol version 2 RSA public key for authentication. The contents of this file should be added to $HOME/.ssh/authorized_keys on all machines where the user wishes to log in using public key authentication. There is no need to keep the con- tents 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 ver- sions 1.5 and 2.0. SEE ALSO
ssh(1), ssh-add(1), ssh-agent(1), sshd(8) J. Galbraith and R. Thayer, SECSH Public Key !FileFormat, draft-ietf-secsh-publickeyfile-01.txt, March2001, work in progress material.BSD September 25, 1999 1
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