ameblo.over-update.download

Aug 25, 2016 Switch (config)# crypto key generate rsa Enables the SSH server for local and remote authentication on the Switch and generates an RSA key pair. Generating an RSA key pair for the Switch automatically enables SSH. We recommend that a minimum modulus size of 1024 bits. When you generate RSA keys, you are prompted to enter a modulus length. Run show crypto key mypubkey rsa to see if you do, in fact, have a key fully generated and registered under a non-default name. If there is, then you can tell the ssh process to use this key with ip ssh rsa keypair-name xxx.If the first command doesn't show anything useful then I'd say you can go ahead and generate a new key. Jan 26, 2018  The ip ssh rsa keypair-name command enables an SSH connection using the Rivest, Shamir, and Adleman (RSA) keys that you have configured. Previously, SSH was linked to the first RSA keys that were generated (that is, SSH was enabled when the first RSA key pair was generated). This behavior still exists, but by using the ip ssh rsa keypair-name command, you can overcome this behavior. DSA for SSH authentication keys. Ask Question Asked 8 years, 9 months ago. To generate a signature, (EC). It's the default RNG in a specific product sold by RSA the corporation, nothing to do with the original RSA public key crypto protocol. – michel-slm Apr 17 '14 at 6:01.

• Hp Procurve Crypto Key Generate Ssh Rsa
• Cisco Switch Can't Generate Crypto Key Rsa

Contents

Introduction

Secure Shell (SSH) is a protocol which provides a secure remote access connection to network devices. Communication between the client and server is encrypted in both SSH version 1 and SSH version 2. Implement SSH version 2 when possible because it uses a more enhanced security encryption algorithm.

This document discusses how to configure and debug SSH on Cisco routers or switches that run a version of Cisco IOS^® Software that supports SSH. This document contains more information on specific versions and software images.

Prerequisites

Requirements

The Cisco IOS image used must be a k9(crypto) image in order to support SSH. For example c3750e-universalk9-tar.122-35.SE5.tar is a k9 (crypto) image.

Components Used

The information in this document is based on Cisco IOS 3600 Software (C3640-IK9S-M), Release 12.2(2)T1.

SSH was introduced into these Cisco IOS platforms and images:

• SSH Version 1.0 (SSH v1) server was introduced in some Cisco IOS platforms and images that start in Cisco IOS Software Release 12.0.5.S.

• SSH client was introduced in some Cisco IOS platforms and images starting in Cisco IOS Software Release 12.1.3.T.

• SSH terminal-line access (also known as reverse-Telnet) was introduced in some Cisco IOS platforms and images starting in Cisco IOS Software Release 12.2.2.T.

• SSH Version 2.0 (SSH v2) support was introduced in some Cisco IOS platforms and images starting in Cisco IOS Software Release 12.1(19)E.

• Refer to How to Configure SSH on Catalyst Switches Running CatOS for more information on SSH support in the switches.

Refer to the Software Advisor (registered customers only) for a complete list of feature sets supported in different Cisco IOS Software releases and on different platforms.

The information presented in this document was created from devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If you are in a live network, make sure that you understand the potential impact of any command before you use it.

Conventions

Refer to Cisco Technical Tips Conventions for more information on document conventions.

SSH v1 vs. SSH v2

Use the Cisco Software Advisor (registered customers only) in order to help you find the version of code with appropriate support for either SSH v1 or SSH v2.

Network Diagram

Test Authentication

Authentication Test without SSH

First test the authentication without SSH to make sure that authentication works with the router Carter before you add SSH. Authentication can be with a local username and password or with an authentication, authorization, and accounting (AAA) server that runs TACACS+ or RADIUS. (Authentication through the line password is not possible with SSH.) This example shows local authentication, which lets you Telnet into the router with username 'cisco' and password 'cisco.'

Authentication Test with SSH

In order to test authentication with SSH, you have to add to the previous statements in order to enable SSH on Carter and test SSH from the PC and UNIX stations.

At this point, the show crypto key mypubkey rsa command must show the generated key. After you add the SSH configuration, test your ability to access the router from the PC and UNIX station. If this does not work, see the debug section of this document.

Optional Configuration Settings

Prevent Non-SSH Connections

If you want to prevent non-SSH connections, add the transport input ssh command under the lines to limit the router to SSH connections only. Straight (non-SSH) Telnets are refused.

Test to make sure that non-SSH users cannot Telnet to the router Carter.

Set Up an IOS Router or Switch as SSH Client

There are four steps required to enable SSH support on a Cisco IOS router:

1. Configure the hostname command.

2. Configure the DNS domain.

3. Generate the SSH key to be used.

4. Enable SSH transport support for the virtual type terminal (vtys).

If you want to have one device act as an SSH client to the other, you can add SSH to a second device called Reed. These devices are then in a client-server arrangement, where Carter acts as the server, and Reed acts as the client. The Cisco IOS SSH client configuration on Reed is the same as required for the SSH server configuration on Carter.

Issue this command to SSH from the Cisco IOS SSH client (Reed) to the Cisco IOS SSH server (Carter) in order to test this:

• SSH v1:

• SSH v2:

Setup an IOS Router as an SSH server that performs RSA based User Authentication

Complete these steps in order to configure the SSH server to perform RSA based authentication.

1. Specify the Host name.

2. Define a default domain name.

3. Generate RSA key pairs.

4. Configure SSH-RSA keys for user and server authentication.

5. Configure the SSH username.

6. Specify the RSA public key of the remote peer.

7. Specify the SSH key type and version. (optional)

8. Exit the current mode and return to privileged EXEC mode.

   Note: Refer to Secure Shell Version 2 Support for more information.

Add SSH Terminal-Line Access

If you need outbound SSH terminal-line authentication, you can configure and test SSH for outbound reverse Telnets through Carter, which acts as a comm server to Philly.

If Philly is attached to Carter's port 2, then you can configure SSH to Philly through Carter from Reed with the help of this command:

• SSH v1:

• SSH v2:

You can use this command from Solaris:

Openssl generate private key certificate request code. In the Features pane (the middle pane), double-click the Server Certificates option located under the IIS or Security heading (depending on your current group-by view). From the Start button select Programs Administrative Tools Internet Information Services Manager. From the Actions pane on the top right, select Create Certificate Request. Open the Internet Information Services (IIS) Manager. In the IIS Manager, select the server node on the top left under Connections.

Restrict SSH access to a subnet

You need to limit SSH connectivity to a specific subnetwork where all other SSH attempts from IPs outside the subnetwork should be dropped.

You can use these steps to accomplish the same:

1. Define an access-list that permits the traffic from that specific subnetwork.

2. Restrict access to the VTY line interface with an access-class.

This is an example configuration. In this example only SSH access to the 10.10.10.0 255.255.255.0 subnet is permitted, any other is denied access.

Note: The same procedure to lock down the SSH access is also applicable on switch platforms.

Configure the SSH Version

Configure SSH v1:

Configure SSH v2:

Configure SSH v1 and v2:

Note: You receive this error message when you use SSHv1:

Note: Cisco bug ID CSCsu51740 (registered customers only) is filed for this issue. Workaround is to configure SSHv2.

Variations on banner Command Output

The banner command output varies between the Telnet and different versions of SSH connections. This table illustrates how different banner command options work with various types of connections.

Unable to Display the Login Banner

SSH version 2 supports the login banner. The login banner is displayed if the SSH client sends the username when it initiates the SSH session with the Cisco router. For example, when the Secure Shell ssh client is used, the login banner is displayed. When the PuTTY ssh client is used, the login banner is not displayed. This is because Secure Shell sends the username by default and PuTTY does not send the username by default.

The Secure Shell client needs the username to initiate the connection to the SSH enabled device. The Connect button is not enabled if you do not enter the host name and username. This screenshot shows that the login banner is displayed when Secure Shell connects to the router. Then, the login banner password prompt displays.

The PuTTY client does not require the username to initiate the SSH connection to the router. This screenshot shows that the PuTTY client connects to the router and prompts for the username and password. It does not display the login banner.

This screen shot shows that the login banner is displayed when PuTTY is configured to send the username to the router.

debug and show Commands

Before you issue the debug commands described and illustrated here, refer to Important Information on Debug Commands. Certain show commands are supported by the Output Interpreter Tool (registered customers only) , which allows you to view an analysis of show command output.

• debug ip ssh—Displays debug messages for SSH.

• show ssh—Displays the status of SSH server connections.

• show ip ssh—Displays the version and configuration data for SSH.

  • Version 1 Connection and no Version 2

  • Version 2 Connection and no Version 1

  • Version 1 and Version 2 Connections

Sample Debug Output

Router Debug

Note: Some of this good debug output is wrapped to multiple lines because of spatial considerations.

Server Debug

Note: This output was captured on a Solaris machine.

What can go Wrong

These sections have sample debug output from several incorrect configurations.

SSH From an SSH Client Not Compiled with Data Encryption Standard (DES)

Solaris Debug

Router Debug

Bad Password

Router Debug

SSH Client Sends Unsupported (Blowfish) Cipher

Router Debug

Geting the '%SSH-3-PRIVATEKEY: Unable to retrieve RSA private key for' Error

If you receive this error message, it may be caused due to any change in the domain name or host name. In order to resolve this, try these workarounds.

• Zeroize the RSA keys and re-generate the keys.

• If the previous workaround does not work, try these steps:

  1. Zeroize all RSA keys.

  2. Reload the device.

  3. Create new labeled keys for SSH.

Cisco bug ID CSCsa83601 (registered customers only) has been filed to address this behaviour.

Troubleshooting Tips

• If your SSH configuration commands are rejected as illegal commands, you have not successfully generated a RSA key pair for your router. Make sure you have specified a host name and domain. Then use the crypto key generate rsa command to generate an RSA key pair and enable the SSH server.

• When you configure the RSA key pair, you might encounter these error messages:

  1. No hostname specified

     You must configure a host name for the router using the hostname global configuration command.

  2. No domain specified

     You must configure a host domain for the router using the ip domain-name global configuration command.

• The number of allowable SSH connections is limited to the maximum number of vtys configured for the router. Each SSH connection uses a vty resource.

• SSH uses either local security or the security protocol that is configured through AAA on your router for user authentication. When you configure AAA, you must ensure that the console is not running under AAA by applying a keyword in the global configuration mode to disable AAA on the console.

• No SSH server connections running.

  This output suggests that the SSH server is disabled or not enabled properly. If you have already configured SSH, it is recommended that you reconfigure the SSH server in the device. Complete these steps in order to reconfigure SSH server on the device.

  1. Delete the RSA key pair. After the RSA key pair is deleted, the SSH server is automatically disabled.

     Note: It is important to generate a key-pair with at least 768 as bit size when you enable SSH v2.

     Caution: This command cannot be undone after you save your configuration, and after RSA keys have been deleted, you cannot use certificates or the CA or participate in certificate exchanges with other IP Security (IPSec) peers unless you reconfigure CA interoperability by regenerating RSA keys, getting the CA's certificate, and requesting your own certificate again.Refer to crypto key zeroize rsa - Cisco IOS Security Command Reference, Release 12.3 for more information on this command.

  2. Reconfigure the hostname and domain name of the device.

  3. Generate an RSA key pair for your router, which automatically enables SSH.

     Refer to crypto key generate rsa - Cisco IOS Security Command Reference, Release 12.3 for more information on the usage of this command.

     Note: You can receive the SSH2 0: Unexpected mesg type received error message due to a packet received that is not understandable by the router. Increase the key length while you generate rsa keys for ssh in order to resolve this issue.

  4. Configure SSH server. In order to enable and configure a Cisco router/switch for SSH server, you can configure SSH parameters. If you do not configure SSH parameters, the default values are used.

     ip ssh {[timeout seconds] [authentication-retries integer]}

     Refer to ip ssh - Cisco IOS Security Command Reference, Release 12.3 for more information on the usage of this command.

Related Information

This article or section needs expansion.

SSH keys can serve as a means of identifying yourself to an SSH server using public-key cryptography and challenge-response authentication. The major advantage of key-based authentication is that in contrast to password authentication it is not prone to brute-force attacks and you do not expose valid credentials, if the server has been compromised.[1]

Furthermore SSH key authentication can be more convenient than the more traditional password authentication. When used with a program known as an SSH agent, SSH keys can allow you to connect to a server, or multiple servers, without having to remember or enter your password for each system.

Key-based authentication is not without its drawbacks and may not be appropriate for all environments, but in many circumstances it can offer some strong advantages. A general understanding of how SSH keys work will help you decide how and when to use them to meet your needs.

This article assumes you already have a basic understanding of the Secure Shell protocol and have installed the openssh package.

• 2Generating an SSH key pair
  • 2.1Choosing the authentication key type
  • 2.2Choosing the key location and passphrase
• 3Copying the public key to the remote server
• 4SSH agents
  • 4.1ssh-agent
  • 4.3Keychain
  • 4.4x11-ssh-askpass
  • 4.5pam_ssh
• 5Troubleshooting

Background

SSH keys are always generated in pairs with one known as the private key and the other as the public key. The private key is known only to you and it should be safely guarded. By contrast, the public key can be shared freely with any SSH server to which you wish to connect.

If an SSH server has your public key on file and sees you requesting a connection, it uses your public key to construct and send you a challenge. This challenge is an encrypted message and it must be met with the appropriate response before the server will grant you access. What makes this coded message particularly secure is that it can only be understood by the private key holder. While the public key can be used to encrypt the message, it cannot be used to decrypt that very same message. Only you, the holder of the private key, will be able to correctly understand the challenge and produce the proper response.

This challenge-response phase happens behind the scenes and is invisible to the user. As long as you hold the private key, which is typically stored in the ~/.ssh/ directory, your SSH client should be able to reply with the appropriate response to the server.

A private key is a guarded secret and as such it is advisable to store it on disk in an encrypted form. When the encrypted private key is required, a passphrase must first be entered in order to decrypt it. While this might superficially appear as though you are providing a login password to the SSH server, the passphrase is only used to decrypt the private key on the local system. The passphrase is not transmitted over the network.

Generating an SSH key pair

An SSH key pair can be generated by running the ssh-keygen command, defaulting to 3072-bit RSA (and SHA256) which the ssh-keygen(1) man page says is 'generally considered sufficient' and should be compatible with virtually all clients and servers:

The randomart image was introduced in OpenSSH 5.1 as an easier means of visually identifying the key fingerprint.

You can also add an optional comment field to the public key with the -C switch, to more easily identify it in places such as ~/.ssh/known_hosts, ~/.ssh/authorized_keys and ssh-add -L output. For example:

will add a comment saying which user created the key on which machine and when.

Choosing the authentication key type

OpenSSH supports several signing algorithms (for authentication keys) which can be divided in two groups depending on the mathematical properties they exploit:

1. DSA and RSA, which rely on the practical difficulty of factoring the product of two large prime numbers,
2. ECDSA and Ed25519, which rely on the elliptic curve discrete logarithm problem. (example)

Elliptic curve cryptography (ECC) algorithms are a more recent addition to public key cryptosystems. One of their main advantages is their ability to provide the same level of security with smaller keys, which makes for less computationally intensive operations (i.e. faster key creation, encryption and decryption) and reduced storage and transmission requirements.

OpenSSH 7.0 deprecated and disabled support for DSA keys due to discovered vulnerabilities, therefore the choice of cryptosystem lies within RSA or one of the two types of ECC.

#RSA keys will give you the greatest portability, while #Ed25519 will give you the best security but requires recent versions of client & server[2]^{[dead link 2020-04-02 ⓘ]}. #ECDSA is likely more compatible than Ed25519 (though still less than RSA), but suspicions exist about its security (see below).

RSA

ssh-keygen defaults to RSA therefore there is no need to specify it with the -t option. It provides the best compatibility of all algorithms but requires the key size to be larger to provide sufficient security.

Minimum key size is 1024 bits, default is 3072 (see ssh-keygen(1)) and maximum is 16384.

If you wish to generate a stronger RSA key pair (e.g. to guard against cutting-edge or unknown attacks and more sophisticated attackers), simply specify the -b option with a higher bit value than the default:

Be aware though that there are diminishing returns in using longer keys.[3][4] The GnuPG FAQ reads: 'If you need more security than RSA-2048 offers, the way to go would be to switch to elliptical curve cryptography — not to continue using RSA'.[5]

On the other hand, the latest iteration of the NSA Fact Sheet Suite B Cryptography^{[dead link 2020-04-02 ⓘ]} suggests a minimum 3072-bit modulus for RSA while '[preparing] for the upcoming quantum resistant algorithm transition'.[6]

ECDSA

The Elliptic Curve Digital Signature Algorithm (ECDSA) was introduced as the preferred algorithm for authentication in OpenSSH 5.7. Some vendors also disable the required implementations due to potential patent issues.

There are two sorts of concerns with it:

1. Political concerns, the trustworthiness of NIST-produced curves being questioned after revelations that the NSA willingly inserts backdoors into softwares, hardware components and published standards were made; well-known cryptographers haveexpresseddoubts about how the NIST curves were designed, and voluntary tainting has already beenproved in the past.
2. Technical concerns, about the difficulty to properly implement the standard and the slowness and design flaws which reduce security in insufficiently precautious implementations.

Both of those concerns are best summarized in libssh curve25519 introduction. Although the political concerns are still subject to debate, there is a clear consensus that #Ed25519 is technically superior and should therefore be preferred.

Ed25519

Ed25519 was introduced in OpenSSH 6.5 of January 2014: 'Ed25519 is an elliptic curve signature scheme that offers better security than ECDSA and DSA and good performance'. Its main strengths are its speed, its constant-time run time (and resistance against side-channel attacks), and its lack of nebulous hard-coded constants.[7] See also this blog post by a Mozilla developer on how it works.

It is already implemented in many applications and libraries and is the default key exchange algorithm (which is different from key signature) in OpenSSH.

Ed25519 key pairs can be generated with:

There is no need to set the key size, as all Ed25519 keys are 256 bits.

Keep in mind that older SSH clients and servers may not support these keys.

Choosing the key location and passphrase

Upon issuing the ssh-keygen command, you will be prompted for the desired name and location of your private key. By default, keys are stored in the ~/.ssh/ directory and named according to the type of encryption used. You are advised to accept the default name and location in order for later code examples in this article to work properly.

When prompted for a passphrase, choose something that will be hard to guess if you have the security of your private key in mind. A longer, more random password will generally be stronger and harder to crack should it fall into the wrong hands.

It is also possible to create your private key without a passphrase. While this can be convenient, you need to be aware of the associated risks. Without a passphrase, your private key will be stored on disk in an unencrypted form. Anyone who gains access to your private key file will then be able to assume your identity on any SSH server to which you connect using key-based authentication. Furthermore, without a passphrase, you must also trust the root user, as he can bypass file permissions and will be able to access your unencrypted private key file at any time.

Changing the private key's passphrase without changing the key

Hp Procurve Crypto Key Generate Ssh Rsa

If the originally chosen SSH key passphrase is undesirable or must be changed, one can use the ssh-keygen command to change the passphrase without changing the actual key. This can also be used to change the password encoding format to the new standard.

Managing multiple keys

It is possible — although controversial [8][9] — to use the same SSH key pair for multiple hosts.

On the other hand, it is rather easy to maintain distinct keys for multiple hosts by using the IdentityFile directive in your openSSH config file:

See ssh_config(5) for full description of these options.

Storing SSH keys on hardware tokens

SSH keys can also be stored on a security token like a smart card or a USB token. This has the advantage that the private key is stored securely on the token instead of being stored on disk. When using a security token the sensitive private key is also never present in the RAM of the PC; the cryptographic operations are performed on the token itself. A cryptographic token has the additional advantage that it is not bound to a single computer; it can easily be removed from the computer and carried around to be used on other computers.

Examples are hardware tokens are described in:

• YubiKey#Using a YubiKey with SSH, and

Copying the public key to the remote server

This article or section needs expansion.

Once you have generated a key pair, you will need to copy the public key to the remote server so that it will use SSH key authentication. The public key file shares the same name as the private key except that it is appended with a .pub extension. Note that the private key is not shared and remains on the local machine.

Simple method

If your key file is ~/.ssh/id_rsa.pub you can simply enter the following command.

If your username differs on remote machine, be sure to prepend the username followed by @ to the server name.

If your public key filename is anything other than the default of ~/.ssh/id_rsa.pub you will get an error stating /usr/bin/ssh-copy-id: ERROR: No identities found. In this case, you must explicitly provide the location of the public key.

If the ssh server is listening on a port other than default of 22, be sure to include it within the host argument.

Manual method

By default, for OpenSSH, the public key needs to be concatenated with ~/.ssh/authorized_keys. Begin by copying the public key to the remote server.

The above example copies the public key (id_ecdsa.pub) to your home directory on the remote server via scp. Do not forget to include the : at the end of the server address. Also note that the name of your public key may differ from the example given.

On the remote server, you will need to create the ~/.ssh directory if it does not yet exist and append your public key to the authorized_keys file.

The last two commands remove the public key file from the server and set the permissions on the authorized_keys file such that it is only readable and writable by you, the owner.

SSH agents

If your private key is encrypted with a passphrase, this passphrase must be entered every time you attempt to connect to an SSH server using public-key authentication. Each individual invocation of ssh or scp will need the passphrase in order to decrypt your private key before authentication can proceed.

An SSH agent is a program which caches your decrypted private keys and provides them to SSH client programs on your behalf. In this arrangement, you must only provide your passphrase once, when adding your private key to the agent's cache. This facility can be of great convenience when making frequent SSH connections.

An agent is typically configured to run automatically upon login and persist for the duration of your login session. A variety of agents, front-ends, and configurations exist to achieve this effect. This section provides an overview of a number of different solutions which can be adapted to meet your specific needs.

ssh-agent

ssh-agent is the default agent included with OpenSSH. It can be used directly or serve as the back-end to a few of the front-end solutions mentioned later in this section. When ssh-agent is run, it forks to background and prints necessary environment variables. E.g.

To make use of these variables, run the command through the eval command.

Once ssh-agent is running, you will need to add your private key to its cache:

If your private key is encrypted, ssh-add will prompt you to enter your passphrase. Once your private key has been successfully added to the agent you will be able to make SSH connections without having to enter your passphrase.

In order to start the agent automatically and make sure that only one ssh-agent process runs at a time, add the following to your ~/.bashrc:

This will run a ssh-agent process if there is not one already, and save the output thereof. If there is one running already, we retrieve the cached ssh-agent output and evaluate it which will set the necessary environment variables.

There also exist a number of front-ends to ssh-agent and alternative agents described later in this section which avoid this problem.

Start ssh-agent with systemd user

It is possible to use the systemd/User facilities to start the agent. Use this if you would like your ssh agent to run when you are logged in, regardless of whether x is running.

Add SSH_AUTH_SOCK DEFAULT='${XDG_RUNTIME_DIR}/ssh-agent.socket' to ~/.pam_environment. Then enable or start the service with the --user flag.

ssh-agent as a wrapper program

An alternative way to start ssh-agent (with, say, each X session) is described in this ssh-agent tutorial by UC Berkeley Labs. A basic use case is if you normally begin X with the startx command, you can instead prefix it with ssh-agent like so:

And so you do not even need to think about it you can put an alias in your .bash_aliases file or equivalent:

Doing it this way avoids the problem of having extraneous ssh-agent instances floating around between login sessions. Exactly one instance will live and die with the entire X session.

See the below notes on using x11-ssh-askpass with ssh-add for an idea on how to immediately add your key to the agent.

GnuPG Agent

The gpg-agent has OpenSSH agent emulation. See GnuPG#SSH agent for necessary configuration.

Keychain

Keychain is a program designed to help you easily manage your SSH keys with minimal user interaction. It is implemented as a shell script which drives both ssh-agent and ssh-add. A notable feature of Keychain is that it can maintain a single ssh-agent process across multiple login sessions. This means that you only need to enter your passphrase once each time your local machine is booted.

Installation

Install the keychain package.

Configuration

Add a line similar to the following to your shell configuration file, e.g. if using Bash:

In the above example,

• the --eval switch outputs lines to be evaluated by the opening eval command; this sets the necessary environments variables for SSH client to be able to find your agent.
• --quiet will limit output to warnings, errors, and user prompts.

Multiple keys can be specified on the command line, as shown in the example. By default keychain will look for key pairs in the ~/.ssh/ directory, but absolute path can be used for keys in non-standard location. You may also use the --confhost option to inform keychain to look in ~/.ssh/config for IdentityFile settings defined for particular hosts, and use these paths to locate keys.

See keychain --help or keychain(1) for details on setting keychain for other shells.

To test Keychain, simply open a new terminal emulator or log out and back in your session. It should prompt you for the passphrase of the specified private key(s) (if applicable), either using the program set in $SSH_ASKPASS or on the terminal.

Because Keychain reuses the same ssh-agent process on successive logins, you should not have to enter your passphrase the next time you log in or open a new terminal. You will only be prompted for your passphrase once each time the machine is rebooted.

Tips

• keychain expects public key files to exist in the same directory as their private counterparts, with a .pub extension. If the private key is a symlink, the public key can be found alongside the symlink or in the same directory as the symlink target (this capability requires the readlink command to be available on the system).

• to disable the graphical prompt and always enter your passphrase on the terminal, use the --nogui option. This allows to copy-paste long passphrases from a password manager for example.

• if you do not want to be immediately prompted for unlocking the keys but rather wait until they are needed, use the --noask option.

x11-ssh-askpass

The x11-ssh-askpass package provides a graphical dialog for entering your passhrase when running an X session. x11-ssh-askpass depends only on the libx11 and libxt libraries, and the appearance of x11-ssh-askpass is customizable. While it can be invoked by the ssh-add program, which will then load your decrypted keys into ssh-agent, the following instructions will, instead, configure x11-ssh-askpass to be invoked by the aforementioned Keychain script.

Install the keychain and x11-ssh-askpass packages.

Edit your ~/.xinitrc file to include the following lines, replacing the name and location of your private key if necessary. Be sure to place these commands before the line which invokes your window manager.

In the above example, the first line invokes keychain and passes the name and location of your private key. If this is not the first time keychain was invoked, the following two lines load the contents of $HOSTNAME-sh and $HOSTNAME-sh-gpg, if they exist. These files store the environment variables of the previous instance of keychain.

Calling x11-ssh-askpass with ssh-add

The ssh-add manual page specifies that, in addition to needing the DISPLAY variable defined, you also need SSH_ASKPASS set to the name of your askpass program (in this case x11-ssh-askpass). It bears keeping in mind that the default Arch Linux installation places the x11-ssh-askpass binary in /usr/lib/ssh/, which will not be in most people's PATH. This is a little annoying, not only when declaring the SSH_ASKPASS variable, but also when theming. You have to specify the full path everywhere. Both inconveniences can be solved simultaneously by symlinking:

This is assuming that ~/bin is in your PATH. So now in your .xinitrc, before calling your window manager, one just needs to export the SSH_ASKPASS environment variable:

and your X resources will contain something like:

Doing it this way works well with the above method on using ssh-agent as a wrapper program. You start X with ssh-agent startx and then add ssh-add to your window manager's list of start-up programs.

Theming

The appearance of the x11-ssh-askpass dialog can be customized by setting its associated X resources. Some examples are the .ad files at https://github.com/sigmavirus24/x11-ssh-askpass. See x11-ssh-askpass(1)^{[dead link 2019-05-05]} for full details.

Alternative passphrase dialogs

There are other passphrase dialog programs which can be used instead of x11-ssh-askpass. The following list provides some alternative solutions.

• ksshaskpass uses the KDE Wallet.
• openssh-askpass uses the Qt library.

pam_ssh

The pam_ssh project exists to provide a Pluggable Authentication Module (PAM) for SSH private keys. This module can provide single sign-on behavior for your SSH connections. On login, your SSH private key passphrase can be entered in place of, or in addition to, your traditional system password. Once you have been authenticated, the pam_ssh module spawns ssh-agent to store your decrypted private key for the duration of the session.

To enable single sign-on behavior at the tty login prompt, install the unofficial pam_ssh^AUR package.

Create a symlink to your private key file and place it in ~/.ssh/login-keys.d/. Replace the id_rsa in the example below with the name of your own private key file.

Edit the /etc/pam.d/login configuration file to include the text highlighted in bold in the example below. The order in which these lines appear is significiant and can affect login behavior.

In the above example, login authentication initially proceeds as it normally would, with the user being prompted to enter his user password. The additional auth authentication rule added to the end of the authentication stack then instructs the pam_ssh module to try to decrypt any private keys found in the ~/.ssh/login-keys.d directory. The try_first_pass option is passed to the pam_ssh module, instructing it to first try to decrypt any SSH private keys using the previously entered user password. If the user's private key passphrase and user password are the same, this should succeed and the user will not be prompted to enter the same password twice. In the case where the user's private key passphrase user password differ, the pam_ssh module will prompt the user to enter the SSH passphrase after the user password has been entered. The optional control value ensures that users without an SSH private key are still able to log in. In this way, the use of pam_ssh will be transparent to users without an SSH private key.

If you use another means of logging in, such as an X11 display manager like SLiM or XDM and you would like it to provide similar functionality, you must edit its associated PAM configuration file in a similar fashion. Packages providing support for PAM typically place a default configuration file in the /etc/pam.d/ directory.

Further details on how to use pam_ssh and a list of its options can be found in the pam_ssh(8) man page.

Using a different password to unlock the SSH key

If you want to unlock the SSH keys or not depending on whether you use your key's passphrase or the (different!) login password, you can modify /etc/pam.d/system-auth to

For an explanation, see [10].

Known issues with pam_ssh

Work on the pam_ssh project is infrequent and the documentation provided is sparse. You should be aware of some of its limitations which are not mentioned in the package itself.

• Versions of pam_ssh prior to version 2.0 do not support SSH keys employing the newer option of ECDSA (elliptic curve) cryptography. If you are using earlier versions of pam_ssh you must use either RSA or DSA keys.

• The ssh-agent process spawned by pam_ssh does not persist between user logins. If you like to keep a GNU Screen session active between logins you may notice when reattaching to your screen session that it can no longer communicate with ssh-agent. This is because the GNU Screen environment and those of its children will still reference the instance of ssh-agent which existed when GNU Screen was invoked but was subsequently killed in a previous logout. The Keychain front-end avoids this problem by keeping the ssh-agent process alive between logins.

pam_exec-ssh

As an alternative to pam_ssh you can use pam_exec-ssh^AUR. It is a shell script that uses pam_exec. Help for configuration can be found upstream.

GNOME Keyring

If you use the GNOME desktop, the GNOME Keyring tool can be used as an SSH agent. See the GNOME Keyring article for further details.

Store SSH keys with Kwallet

For instructions on how to use kwallet to store your SSH keys, see KDE Wallet#Using the KDE Wallet to store ssh key passphrases.

KeePass2 with KeeAgent plugin

KeeAgent is a plugin for KeePass that allows SSH keys stored in a KeePass database to be used for SSH authentication by other programs.

• Supports both PuTTY and OpenSSH private key formats.
• Works with native SSH agent on Linux/Mac and with PuTTY on Windows.

See KeePass#Plugin Installation in KeePass or install the keepass-plugin-keeagent package.

This agent can be used directly, by matching KeeAgent socket: KeePass -> Tools -> Options -> KeeAgent -> Agent mode socket file -> %XDG_RUNTIME_DIR%/keeagent.socket-and environment variable:export SSH_AUTH_SOCK='$XDG_RUNTIME_DIR'/keeagent.socket'.

KeePassXC

Cisco Switch Can't Generate Crypto Key Rsa

The KeePassXC fork of KeePass supports being used as an SSH agent by default. It is also compatible with KeeAgent's database format.

Troubleshooting

Key ignored by the server

• If it appears that the SSH server is ignoring your keys, ensure that you have the proper permissions set on all relevant files.

For the local machine:

For the remote machine:

• If that does not solve the problem you may try temporarily setting StrictModes to no in /etc/ssh/sshd_config. If authentication with StrictModes off is successful, it is likely an issue with file permissions persists.

• Make sure keys in ~/.ssh/authorized_keys are entered correctly and only use one single line.
• Make sure the remote machine supports the type of keys you are using: some servers do not support ECDSA keys, try using RSA or DSA keys instead, see #Generating an SSH key pair.
• You may want to use debug mode and monitor the output while connecting:

See also

• OpenSSH key management: Part 1, Part 2, Part 3