SSH 鍵
SSH 鍵は公開鍵暗号とチャレンジ/レスポンス認証を使って SSH サーバーに自身を確認させる手段として用います。伝統的なパスワード認証と比べてこの方法を使用する利点として、ネットワークを介してパスワードを送信しなくてもサーバーから認証を受けられるということが挙げられます。パスワードを転送しているわけではないので、たとえ接続を盗聴されてもパスワードを盗まれたりクラックされる恐れがありません。さらに、SSH 鍵を使って認証をすることによって、ブルートフォース攻撃を受けるリスクを事実上なくすことができます。攻撃者が正しい証明書を得られる確率は劇的に減るからです。
セキュリティの向上につながるという他に、SSH 鍵認証は伝統的なパスワード認証よりも便利だという点もあります。SSH エージェントというプログラムを使うことで、システムごとのパスワードを記録して入力する必要はなくなり、SSH 鍵でサーバーに接続することが可能になります。
SSH 鍵に全く欠点がないというわけではなく、環境によっては相応しくないという場合もありますが、大抵の場合は SSH 鍵を使用することには強力なメリットが望めます。SSH 鍵の動作方法を理解することは、いつ、どのように鍵を使えば要求を満たせるのか考える手がかりになるでしょう。この記事では Secure Shell プロトコルについての基本的な知識を持っていて、公式リポジトリの openssh パッケージを既にインストールしていることを前提としています。
予備知識
SSH 鍵は常にペアで存在します。公開鍵と秘密鍵です。秘密鍵はあなたしか知らない鍵で、安全に保管する必要があります。逆に、公開鍵は接続したい SSH サーバーと自由に共有できます。
ファイル形式の公開鍵が SSH サーバーに存在し、あなたが接続をリクエストしたことを確認したら、SSH サーバーは公開鍵を使ってチャレンジをあなたに作成・送信します。このチャレンジは暗号文のようなもので、適切なレスポンスを返すことによって、アクセス権がサーバーによって与えられます。暗号文を解読できるのは秘密鍵を持っている人だけということが、暗号文を特に安全なものにしています。公開鍵を使ってメッセージを暗号化することはできる一方で、公開鍵を使ってメッセージを復号化することはできません。秘密鍵を持っている、あなただけが、チャレンジを解読して適切なレスポンスを作成することができるわけです。
このチャレンジ/レスポンス認証は水面下で行われ、ユーザーが関知するところではありません。秘密鍵を持ってさえいれば (通常は ~/.ssh/ ディレクトリに鍵が保存されます)、SSH クライアントはサーバーに適切なレスポンスを返すことが可能です。
秘密鍵は機密情報として考えてよく、暗号化されてディスクに保存されることもよくあります。この場合、秘密鍵が必要になったとき、最初にパスフレーズを入力して秘密鍵を復号化する必要があります。表面的には、SSH サーバーにログインパスワードを入力するのと変わりないように見えますが、実際にはローカルシステム上の秘密鍵を復号化するためのパスフレーズです。このパスフレーズはネットワークを介して送信されることはありませんし、送信するなんて言語道断です。
SSH 鍵のペアを生成
SSH 鍵のペアは ssh-keygen コマンドを実行することで生成できます:
$ ssh-keygen -t rsa -b 4096 -C "$(whoami)@$(hostname)-$(date -I)"
Generating public/private rsa key pair. Enter file in which to save the key (/home/username/.ssh/id_rsa): Enter passphrase (empty for no passphrase): Enter same passphrase again: Your identification has been saved in /home/username/.ssh/id_rsa. Your public key has been saved in /home/username/.ssh/id_rsa.pub. The key fingerprint is: dd:15:ee:24:20:14:11:01:b8:72:a2:0f:99:4c:79:7f username@localhost-2014-11-22 The key's randomart image is: +--[RSA 4096]---+ | ..oB=. . | | . . . . . | | . . . + | | oo.o . . = | |o+.+. S . . . | |=. . E | | o . | | . | | | +-----------------+
In the above example, ssh-keygen generates a 4096 bit long (-b 4096) public/private RSA (-t rsa) key pair with an extended comment including the data (-C "$(whoami)@$(hostname)-$(date -I)"). The randomart image was introduced in OpenSSH 5.1 as an easier means of visually identifying the key fingerprint.
暗号化のタイプを選択
The Elliptic Curve Digital Signature Algorithm (ECDSA) provides smaller key sizes and faster operations for equivalent estimated security to the previous methods. It was introduced as the preferred algorithm for authentication in OpenSSH 5.7, see OpenSSH 5.7 Release Notes. ECDSA keys might not be compatible with systems that ship old versions of OpenSSH. Some vendors also disable the required implementations due to potential patent issues.
OpenSSH 6.5 から Ed25519 鍵がサポートされています: "Ed25519 は楕円曲線による署名方式で、ECDSA や DSA よりも安全なセキュリティ、高いパフォーマンスを実現します" [1]。Ed25519 鍵は ssh-keygen -t ed25519 で生成できます。鍵長を設定する必要はありません。全ての Ed25519 鍵は256ビットです。
If you choose to create an RSA (2048-16384 bit) or DSA (2048 bit) key pair instead, use the -t rsa or -t dsa switches in your ssh-keygen command and do not forget to increase the key size. Running ssh-keygen without the -b switch should provide reasonable defaults.
鍵の場所とパスフレーズを選択
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.
鍵を変更せずに秘密鍵のパスフレーズを変更する
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.
To change the passphrase for the private RSA key, run the following command:
$ ssh-keygen -f ~/.ssh/id_rsa -p
複数の鍵の管理
It's possible to manage keys per host by creating the file ~/.ssh/config and assigning each host another key for authentication if needed. Actually it's not needed, because you could use the same identity for each host. Yet, you don't want to use the same key for each client, then create this file like shown here:
Host SERVERNAME1 IdentitiesOnly yes IdentityFile ~/.ssh/id_rsa_SERVER1 # CheckHostIP yes # Port 22 Host SERVERNAME2 IdentitiesOnly yes IdentityFile ~/.ssh/id_rsa_SERVER2 # CheckHostIP no # Port 2177 ControlMaster auto ControlPath /tmp/%r@%h:%p
Many more options you will find with
$ man ssh_config 5
リモートサーバーに公開鍵をコピー
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.
シンプルな方法
If your key file is ~/.ssh/id_rsa.pub you can simply enter the following command.
$ ssh-copy-id remote-server.org
If your username differs on remote machine, be sure to prepend the username followed by @ to the server name.
$ ssh-copy-id username@remote-server.org
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.
$ ssh-copy-id -i ~/.ssh/id_ecdsa.pub username@remote-server.org
If the ssh server is listening on a port other than default of 22, be sure to include it within the host argument.
$ ssh-copy-id -i ~/.ssh/id_ecdsa.pub -p 221 username@remote-server.org
伝統的な方法
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.
$ scp ~/.ssh/id_ecdsa.pub username@remote-server.org:
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.
$ ssh username@remote-server.org username@remote-server.org's password: $ mkdir ~/.ssh $ chmod 700 ~/.ssh $ cat ~/id_ecdsa.pub >> ~/.ssh/authorized_keys $ rm ~/id_ecdsa.pub $ chmod 600 ~/.ssh/authorized_keys
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.
セキュリティ
authorized_keys ファイルの保全
さらなる保護のため、ユーザーが新しい公開鍵を追加して接続することを禁止させることができます。
Make the authorized_keys file read-only for the user and deny all other permissions:
$ chmod 400 ~/.ssh/authorized_keys
To keep the user from simply changing the permissions back, set the immutable bit on the authorized_keys file. After that the user could rename the ~/.ssh directory to something else and create a new ~/.ssh directory and authorized_keys file. To prevent this, set the immutable bit on the ~/.ssh directory too.
パスワードログインの無効化
While copying your public key to the remote SSH server eliminates the need to transmit your password over the network, it does not give any added protection against a brute-force password attack. In the absence of a private key, the SSH server will fall back to password authentication by default, thus allowing a malicious user to attempt to gain access by guessing your password. To disable this behavior, edit the following lines in the /etc/ssh/sshd_config file on the remote server.
/etc/ssh/sshd_config
PasswordAuthentication no ChallengeResponseAuthentication no
2段階認証と公開鍵
OpenSSH 6.2 から、AuthenticationMethods オプションを使って自分でチェインを追加して認証することができるようになりました。これによって公開鍵だけでなく2段階認証が使うことができます。
Google Authenticator のセットアップについては Google Authenticator を見て下さい。
OpenSSH で PAM を使うには、以下のファイルを編集します:
/etc/ssh/sshd_config
ChallengeResponseAuthentication yes AuthenticationMethods publickey keyboard-interactive:pam
Then you can log in with either a publickey or the user authentication as required by your PAM setup.
If, on the other hand, you want to authenticate the user on both a publickey and the user authentication as required by your PAM setup, use a comma instead of a space to separate the AuthenticationMethods:
/etc/ssh/sshd_config
ChallengeResponseAuthentication yes AuthenticationMethods publickey,keyboard-interactive:pam
SSH エージェント
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 は OpenSSH に含まれているデフォルトのエージェントです。直接使用することもできますし、後のセクションで触れている、フロントエンドのためのバックエンドとして使うこともできます。ssh-agent が実行されると、ssh-agent は自分をバックグラウンドにフォークして、使用する環境変数を出力します。
$ ssh-agent SSH_AUTH_SOCK=/tmp/ssh-vEGjCM2147/agent.2147; export SSH_AUTH_SOCK; SSH_AGENT_PID=2148; export SSH_AGENT_PID; echo Agent pid 2148;
これらの変数を利用するには、eval コマンドを通してコマンドを実行してください。
$ eval $(ssh-agent) Agent pid 2157
You can append the above command to your ~/.bash_profile script so that it will run automatically when starting a login shell.
$ echo 'eval $(ssh-agent)' >> ~/.bash_profile
Once ssh-agent is running, you will need to add your private key to its cache.
$ ssh-add ~/.ssh/id_ecdsa Enter passphrase for /home/user/.ssh/id_ecdsa: Identity added: /home/user/.ssh/id_ecdsa (/home/user/.ssh/id_ecdsa)
If you would like your private keys to be added automatically on login. Add the following command to your ~/.bash_profile as well.
$ ssh-add
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 a passphrase.
If you would prefer not to be prompted for your passphrase until your key is needed, adding
$ ssh-add -l >/dev/null || alias ssh='ssh-add -l >/dev/null || ssh-add && unalias ssh; ssh'
to ~/.bashrc will cause ssh-add to be run when needed and destroy the alias afterwards.
One downside to this approach is that a new instance of ssh-agent is created for every login shell and each instance will persist between login sessions. Over time you can wind up with dozens of needless ssh-agent processes running. There exist a number of front-ends to ssh-agent and alternative agents described later in this section which avoid this problem.
Another downside is that the key will not be added by commands other than ssh that use the private key, such as many git commands.
systemd ユーザーで ssh-agent を起動
Systemd/ユーザー機能を使ってエージェントを起動することができます。~/.config/systemd/user フォルダに以下のユニットファイルを配置してください:
ssh-agent.service
[Unit] Description=SSH key agent [Service] Type=forking Environment=SSH_AUTH_SOCK=%t/ssh-agent.socket ExecStart=/usr/bin/ssh-agent -a $SSH_AUTH_SOCK [Install] WantedBy=MyTarget.target
Add export SSH_AUTH_SOCK="$XDG_RUNTIME_DIR/ssh-agent.socket" to your shell's startup file, for example .bash_profile for Bash.
Then enable and start the service.
ssh-agent をラッパープログラムとして使う
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:
$ ssh-agent startx
And so you don't even need to think about it you can put an alias in your .bash_aliases file or equivalent:
alias startx='ssh-agent startx'
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 エージェント
公式リポジトリ の gnupg パッケージに入っている GnuPG エージェントには OpenSSH エージェントのエミュレーションがあります。GnuPG スイートを既に使っている場合は、GnuPG エージェントを使って SSH 鍵をキャッシュすることが可能です。さらに、場合によっては GnuPG エージェントがパスフレーズ管理の一部として提供している PIN エントリダイアログを使うのも良いでしょう。
To start using GnuPG agent for your SSH keys, you should first start gpg-agent with the --enable-ssh-support option. Example (do not forget to make the file executable):
/etc/profile.d/gpg-agent.sh
#!/bin/sh
# Start the GnuPG agent and enable OpenSSH agent emulation
gnupginf="${HOME}/.gpg-agent-info"
if pgrep -x -u "${USER}" gpg-agent >/dev/null 2>&1; then
eval `cat $gnupginf`
eval `cut -d= -f1 $gnupginf | xargs echo export`
else
eval `gpg-agent -s --enable-ssh-support --daemon --write-env-file "$gnupginf"`
fi
Once gpg-agent is running you can use ssh-add to approve keys, just like you did with plain ssh-agent. The list of approved keys is stored in the ~/.gnupg/sshcontrol file. Once your key is approved, you will get a PIN entry dialog every time your passphrase is needed. You can control passphrase caching in the ~/.gnupg/gpg-agent.conf file. The following example would have gpg-agent cache your keys for 3 hours:
~/.gnupg/gpg-agent.conf
# Cache settings default-cache-ttl 10800 default-cache-ttl-ssh 10800
Other useful settings for this file include the PIN entry program (GTK, QT, or ncurses version), keyboard grabbing, and so on...
~/.gnupg/gpg-agent.conf
# Environment file
write-env-file /home/username/.gpg-agent-info
# Keyboard control
#no-grab
# PIN entry program
#pinentry-program /usr/bin/pinentry-curses
#pinentry-program /usr/bin/pinentry-qt4
#pinentry-program /usr/bin/pinentry-kwallet
pinentry-program /usr/bin/pinentry-gtk-2
To use the agent, you can then source and export the environment variables that gpg-agent writes in .gpg-agent-info, which is the file specified with write-env-file.
~/.bashrc
...
if [ -f "${HOME}/.gpg-agent-info" ]; then
. "${HOME}/.gpg-agent-info"
export GPG_AGENT_INFO
export SSH_AUTH_SOCK
fi
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.
Install the keychain package, available from the official repositories.
Append the following line to ~/.bash_profile:
~/.bash_profile
eval $(keychain --eval --agents ssh -Q --quiet id_ecdsa)
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. The --agents switch is not strictly necessary because Keychain will build the list automatically based on the existence of ssh-agent or gpg-agent on the system. Adding the --quiet switch will limit output to warnings, errors, and user prompts. If you want greater security, replace -Q with --clear but will be less convenient.
If necessary, replace ~/.ssh/id_ecdsa with the path to your private key. For those using a non-Bash compatible shell, see keychain --help or man keychain for details on other shells.
To test Keychain, log out from your session and log back in. If this is your first time running Keychain, it will prompt you for the passphrase of the specified private key. 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. You will only be prompted for your passphrase once each time the machine is rebooted.
envoy
An alternative to keychain is envoy. Envoy is available as envoy in the official repositories, or the Git version is in the AUR as envoy-gitAUR.
After installing it, set up the envoy socket with
# systemctl enable envoy@ssh-agent.socket
And add to your shell's rc file:
envoy -t ssh-agent -a ssh_key source <(envoy -p)
If the key is ~/.ssh/id_rsa, ~/.ssh/id_dsa, ~/.ssh/id_ecdsa, or ~/.ssh/identity, the -a ssh_key parameter is not needed.
envoy で kwallet に キーパスフレーズを保存
If you have long passphrases for your SSH keys, remembering them can be a pain. So let us tell kwallet to store them! Along with envoy, install ksshaskpass and kdeutils-kwalletmanager from the official repositories. Next, enable the envoy socket in systemd (see above).
First, you will add this script to ~/.kde4/Autostart/ssh-agent.sh:
#!/bin/sh envoy -t ssh-agent -a ssh_key
Then, make sure the script is executable by running: chmod +x ~/.kde4/Autostart/ssh-agent.sh
And add this to ~/.kde4/env/ssh-agent.sh:
#!/bin/sh eval $(envoy -p)
When you log into KDE, it will execute the ssh-agent.sh script. This will call ksshaskpass, which will prompt you for your kwallet password when envoy calls ssh-agent.
x11-ssh-askpass
The x11-ssh-askpass package provides a graphical dialog for entering your passhrase when running an X session. x11-ssh-askpass depends only on the libx11 and libxt libraries, and the appearance of x11-ssh-askpass is customizable. While it can be invoked by the ssh-add program, which will then load your decrypted keys into ssh-agent, the following instructions will, instead, configure x11-ssh-askpass to be invoked by the aforementioned Keychain script.
Install keychain and x11-ssh-askpass, both available in the official repositories.
Edit your ~/.xinitrc file to include the following lines, replacing the name and location of your private key if necessary. Be sure to place these commands before the line which invokes your window manager.
~/.xinitrc
keychain ~/.ssh/id_ecdsa [ -f ~/.keychain/$HOSTNAME-sh ] && . ~/.keychain/$HOSTNAME-sh 2>/dev/null [ -f ~/.keychain/$HOSTNAME-sh-gpg ] && . ~/.keychain/$HOSTNAME-sh-gpg 2>/dev/null ... exec openbox-session
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.
ssh-add で x11-ssh-askpass を呼び出す
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:
$ ln -sv /usr/lib/ssh/x11-ssh-askpass ~/bin/ssh-askpass
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:
$ export SSH_ASKPASS=ssh-askpass
and your X resources will contain something like:
ssh-askpass*background: #000000
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.
テーマ
The appearance of the x11-ssh-askpass dialog can be customized by setting its associated X resources. The x11-ssh-askpass home page presents some example themes. See the x11-ssh-askpass manual page for full details.
他のパスフレーズダイアログ
There are other passphrase dialog programs which can be used instead of x11-ssh-askpass. The following list provides some alternative solutions.
- ksshaskpass is available in the official repositories. It is dependent on kdelibs and is suitable for the KDE Desktop Environment.
- openssh-askpass depends on the qt4 libraries and is available from the official repositories.
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_sshAUR package, available in the Arch User Repository.
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.
$ mkdir ~/.ssh/login-keys.d/ $ cd ~/.ssh/login-keys.d/ $ ln -s ../id_rsa
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.
/etc/pam.d/login
#%PAM-1.0 auth required pam_securetty.so auth requisite pam_nologin.so auth include system-local-login auth optional pam_ssh.so try_first_pass account include system-local-login session include system-local-login session optional pam_ssh.so
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 man page.
pam_ssh の既知の問題
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-agentprocess 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.
GNOME Keyring
GNOME デスクトップを使用する場合、GNOME Keyring ツールを SSH エージェントとして使うことができます。詳しくは GNOME Keyring の記事を見て下さい。
トラブルシューティング
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:
$ chmod 700 ~/ $ chmod 700 ~/.ssh $ chmod 600 ~/.ssh/id_ecdsa
For the remote machine:
$ chmod 700 ~/ $ chmod 700 ~/.ssh $ chmod 600 ~/.ssh/authorized_keys
If that does not solve the problem you may try temporarily setting StrictModes to no in sshd_config. If authentication with StrictModes off is successful, it is likely an issue with file permissions persists.
Make sure the remote machine supports the type of keys you are using. Try using RSA or DSA keys instead #Generating an SSH key pair
Some servers do not support ECDSA keys.
Failing this, run the sshd in debug mode and monitor the output while connecting:
# /usr/bin/sshd -d
kdm を使う
KDM doesn't launch the ssh-agent process directly, kde-agent used to start ssh-agent on login, but since version 20140102-1 it got removed.
In order to start ssh-agent on KDE startup for a user, create scripts to start ssh-agent on startup and one to kill it on logoff:
echo -e '#!/bin/sh\n[ -n "$SSH_AGENT_PID" ] || eval "$(ssh-agent -s)"' > ~/.kde4/env/ssh-agent-startup.sh echo -e '#!/bin/sh\n[ -z "$SSH_AGENT_PID" ] || eval "$(ssh-agent -k)"' > ~/.kde4/shutdown/ssh-agent-shutdown.sh chmod 755 ~/.kde4/env/ssh-agent-startup.sh ~/.kde4/shutdown/ssh-agent-shutdown.sh
Plasma 5 を使用している場合、~/.kde4 ではなく ~/.config/plasma-workspace/ ディレクトリにスクリプトを作成してください:
echo -e '#!/bin/sh\n[ -n "$SSH_AGENT_PID" ] || eval "$(ssh-agent -s)"' > ~/.config/plasma-workspace/env/ssh-agent-startup.sh echo -e '#!/bin/sh\n[ -z "$SSH_AGENT_PID" ] || eval "$(ssh-agent -k)"' > ~/.config/plasma-workspace/shutdown/ssh-agent-shutdown.sh chmod 755 ~/.config/plasma-workspace/env/ssh-agent-startup.sh ~/.config/plasma-workspace/shutdown/ssh-agent-shutdown.sh