SSH 鍵のソースを表示

[[Category:Secure Shell]]
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SSH 鍵は[[Wikipedia:ja:公開鍵暗号|公開鍵暗号]]と[[Wikipedia:Challenge-response authentication|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 {{Pkg|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から与えられます。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 {{ic|~/.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 {{ic|ssh-keygen}} コマンドを実行することで生成できます:

{{hc
|$ ssh-keygen -t rsa -b 4096 -C "$(whoami)@$(hostname)-$(date -I)"
|<nowiki>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    .          |
|  .              |
|                 |
+-----------------+</nowiki>}}

上記の例では、{{ic|ssh-keygen}} は4096ビット長 ({{ic|-b 4096}}) の公開/秘密 RSA ({{ic|-t rsa}}) 鍵のペアを作成しています。拡張コメントにデータが含まれています ({{ic|-C "$(whoami)@$(hostname)-$(date -I)"}})。OpenSSH 5.1 から [http://www.cs.berkeley.edu/~dawnsong/papers/randomart.pdf ランダムな画像イメージ] が表示されるようになっており、鍵の指紋を視覚的に表しています。

===暗号化のタイプを選択===
エドワーズ曲線デジタル署名アルゴリズム (ECDSA) は小さな鍵長で高速な操作を実現します、セキュリティについては昔の方法と変わりありません。ECDSA は OpenSSH 5.7 で導入され、認証用の推奨アルゴリズムとされています。[http://www.openssh.com/txt/release-5.7 OpenSSH 5.7 のリリースノート] を参照。'''ECDSA 鍵は旧バージョンの OpenSSH を使っているシステムと互換性がない場合があります。'''また、特許の問題を考慮して、メーカーによっては必要な実装が無効化されていることがあります。
{{Warning|There is [http://safecurves.cr.yp.to/rigid.html reason to be suspicious] of the NIST curves used to generate ECDSA keys. Depending on the threat model, it might be advisable to use Ed25519 or RSA.}}
{{Note|2013年12月28日現在、Windows の SSH クライアントである PuTTY は ECDSA をサポートしておらず、ECDSA 鍵を使用しているサーバーに接続することができません。}}
{{Note|1=2014年6月10日現在、ECDSA 鍵は GNOME Keyring で使用できません。[https://bugzilla.gnome.org/show_bug.cgi?id=641082 GNOME の既知のバグ] のためです。}}

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" [http://www.openssh.com/txt/release-6.5]。Ed25519 鍵は {{ic|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。

RSA (2048-16384ビット) または DSA (2048ビット) の鍵対を作成する場合、{{ic|ssh-keygen}} コマンドで {{ic|-t rsa}} または {{ic|-t dsa}} スイッチを使用して、忘れずに鍵長を増やして下さい。{{ic|-b}} スイッチを書かずに {{ic|ssh-keygen}} を実行することで作成されるデフォルトの鍵長で問題ありません。

{{Note|鍵が使用されるのは認証を行うときだけです。強固な鍵にすることで、SSH によってデータを送信する際の CPU の負担が増えることはありません。}}

===鍵の場所とパスフレーズを選択===
{{ic|ssh-keygen}} コマンドの実行時に、秘密鍵の名前と保存場所について尋ねられます。デフォルトでは、鍵は {{ic|~/.ssh/}} ディレクトリに保存され、名前は使用する暗号化のタイプに合わせて付けられます。この記事に出てくるサンプルコードをそのまま使用できるようにするため、デフォルトの名前と場所を使うことを推奨します。

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====
最初に作成した SSH 鍵のパスフレーズがあまりよろしくなくて変更しなくてはならない場合、{{ic|ssh-keygen}} コマンドを使うことで、実際の鍵を変更することなくパスフレーズだけ変更することができます。

RSA 秘密鍵のパスフレーズを変更するには、次を実行:
 $ 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 {{ic|~/.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==
鍵対を生成したら、公開鍵をリモートサーバーにコピーして、SSH 鍵認証が使えるようにする必要があります。公開鍵のファイル名は秘密鍵のファイル名に {{ic|.pub}} 拡張子を付けたものになります。秘密鍵は共有せず、ローカルマシンに残しておくようにしてください。

===シンプルな方法===

{{Note|1=この方法はリモートサーバーが {{ic|sh}} 以外のシェル ({{ic|tcsh}} など) をデフォルトで使っている場合、失敗します。[https://bugzilla.redhat.com/show_bug.cgi?id=1045191 このバグレポート] を参照。}}

鍵のファイルが {{ic|~/.ssh/id_rsa.pub}} の場合、次のコマンドを実行します。
 $ ssh-copy-id remote-server.org

リモートマシンでユーザー名が異なる場合、サーバーの名前の前に {{ic|@}} とユーザー名を書きます。
 $ ssh-copy-id username@remote-server.org

公開鍵のファイル名がデフォルトの {{ic|~/.ssh/id_rsa.pub}} ではない場合、{{ic|/usr/bin/ssh-copy-id: ERROR: No identities found}} というエラーが表示されます。その場合、公開鍵の場所を明示してください。
 $ ssh-copy-id -i ~/.ssh/id_ecdsa.pub username@remote-server.org

ssh サーバーがデフォルトの22番ポート以外を使っている場合、ポート番号を付して下さい。
 $ 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 {{ic|~/.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 ({{ic|id_ecdsa.pub}}) to your home directory on the remote server via {{ic|scp}}.  Do not forget to include the {{ic|:}} 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 {{ic|~/.ssh}} directory if it does not yet exist and append your public key to the {{ic|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 {{ic|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 {{ic|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, [[File permissions and attributes#chattr and lsattr|set the immutable bit]] on the {{ic|authorized_keys}} file. After that the user could rename the {{ic|~/.ssh}} directory to something else and create a new {{ic|~/.ssh}} directory and {{ic|authorized_keys}} file. To prevent this, set the immutable bit on the {{ic|~/.ssh}} directory too.

{{Note|If you find yourself needing to add a new key, you will first have to remove the immutable bit from {{ic|authorized_keys}} and make it writable. Follow the steps above to secure it again.}}

===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 {{ic|/etc/ssh/sshd_config}} file on the remote server.

{{hc|/etc/ssh/sshd_config|
PasswordAuthentication no
ChallengeResponseAuthentication no}}

=== 2段階認証と公開鍵 ===

OpenSSH 6.2 から、{{ic|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:

{{hc|/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:

{{hc|/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 {{ic|ssh}} or {{ic|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。{{ic|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、{{ic|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 {{ic|~/.bash_profile}} script so that it will run automatically when starting a login shell.
 
 $ echo 'eval $(ssh-agent)' >> ~/.bash_profile

Once {{ic|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 {{ic|~/.bash_profile}} as well.

 $ ssh-add

If your private key is encrypted, {{ic|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 {{ic|~/.bashrc}} will cause {{ic|ssh-add}} to be run when needed and destroy the alias afterwards.

One downside to this approach is that a new instance of {{ic|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 {{ic|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。{{ic|~/.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:

{{hc|ssh-agent.service|<nowiki>
[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=</nowiki>''MyTarget''.target
}}

Add {{ic|1=export SSH_AUTH_SOCK="$XDG_RUNTIME_DIR/ssh-agent.socket"}} to your shell's startup file, for example {{ic|.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 [http://upc.lbl.gov/docs/user/sshagent.shtml this ssh-agent tutorial by UC Berkeley Labs]. A basic use case is if you normally begin X with the {{ic|startx}} command, you can instead prefix it with {{ic|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 {{ic|.bash_aliases}} file or equivalent:

 alias startx='ssh-agent startx'

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

{{note|You can also add {{ic|eval $(ssh-agent)}} to {{ic|~/.xinitrc}}.}}

See [[#Calling_x11-ssh-askpass_with_ssh-add|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 {{Pkg|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。

{{Note|If you are using KDE and have {{Pkg|kde-agent}} installed you only need to set {{ic|enable-ssh-support}} into {{ic|~/.gnupg/gpg-agent.conf}}! Otherwise, continue reading.}}

To start using GnuPG agent for your SSH keys, you should first start ''gpg-agent'' with the {{ic|--enable-ssh-support}} option. Example (do not forget to make the file executable):
{{hc|/etc/profile.d/gpg-agent.sh|<nowiki>
#!/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
</nowiki>}}

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 {{ic|~/.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 {{ic|~/.gnupg/gpg-agent.conf}} file. The following example would have ''gpg-agent'' cache your keys for 3 hours: 
{{hc|~/.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...

{{Note|{{ic|gpg-agent.conf}} must be created, and the variable {{ic|write-env-file}} must be set in order to allow ''gpg-agent'' keys to be injected to SSH across logins, unless you restart ''gpg-agent'', and therefore, export its settings, with every login.}}
{{hc|~/.gnupg/gpg-agent.conf|<nowiki>
  # 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

</nowiki>}}

To use the agent, you can then source and export the environment variables that ''gpg-agent'' writes in {{ic|.gpg-agent-info}}, which is the file specified with {{ic|write-env-file}}.
{{hc|~/.bashrc|<nowiki>
...

if [ -f "${HOME}/.gpg-agent-info" ]; then
  . "${HOME}/.gpg-agent-info"
  export GPG_AGENT_INFO
  export SSH_AUTH_SOCK
fi
</nowiki>}}

===Keychain===
[http://www.funtoo.org/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.

[[pacman|Install]] the {{Pkg|keychain}} package, available from the [[official repositories]].

Append the following line to {{ic|~/.bash_profile}}:
{{hc|~/.bash_profile|
eval $(keychain --eval --agents ssh -Q --quiet id_ecdsa)
}}

In the above example, the {{ic|--eval}} switch outputs lines to be evaluated by the opening {{ic|eval}} command. This sets the necessary environments variables for SSH client to be able to find your agent. The {{ic|--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 {{ic|--quiet}} switch will limit output to warnings, errors, and user prompts. If you want greater security, replace {{ic|-Q}} with {{ic|--clear}} but will be less convenient.

If necessary, replace {{ic|~/.ssh/id_ecdsa}} with the path to your private key. For those using a non-Bash compatible shell, see {{ic|keychain --help}} or {{ic|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 [https://github.com/vodik/envoy envoy]. Envoy is available as {{Pkg|envoy}} in the [[official repositories]], or the Git version is in the [[AUR]] as {{AUR|envoy-git}}.

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 {{ic|~/.ssh/id_rsa}}, {{ic|~/.ssh/id_dsa}}, {{ic|~/.ssh/id_ecdsa}}, or {{ic|~/.ssh/identity}}, the {{ic|-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 {{Pkg|envoy}}, install {{Pkg|ksshaskpass}} and {{Pkg|kdeutils-kwalletmanager}} from the [[official repositories]]. Next, enable the envoy socket in systemd (see above).

First, you will add this script to {{ic|~/.kde4/Autostart/ssh-agent.sh}}:
 #!/bin/sh
 envoy -t ssh-agent -a ''ssh_key''
Then, make sure the script is executable by running: {{ic|chmod +x ~/.kde4/Autostart/ssh-agent.sh}}

And add this to {{ic|~/.kde4/env/ssh-agent.sh}}:
 #!/bin/sh
 eval $(envoy -p)

When you log into KDE, it will execute the {{ic|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 {{pkg|x11-ssh-askpass}} package provides a graphical dialog for entering your passhrase when running an X session. ''x11-ssh-askpass'' depends only on the {{Pkg|libx11}} and {{Pkg|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|ssh-agent]], the following instructions will, instead, configure ''x11-ssh-askpass'' to be invoked by the aforementioned [[#Keychain|Keychain]] script.

Install {{Pkg|keychain}} and {{Pkg|x11-ssh-askpass}}, both available in the [[official repositories]].

Edit your {{ic|~/.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.

{{hc|~/.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 {{ic|$HOSTNAME-sh}} and {{ic|$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 {{ic|DISPLAY}} variable defined, you also need {{ic|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 {{ic|/usr/lib/ssh/}}, which will not be in most people's {{ic|PATH}}. This is a little annoying, not only when declaring the {{ic|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 {{ic|~/bin}} is in your {{ic|PATH}}. So now in your {{ic|.xinitrc}}, before calling your window manager, one just needs to export the {{ic|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 [[#ssh-agent_as_a_wrapper_program|the above method on using ''ssh-agent'' as a wrapper program]]. You start X with {{ic|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'' [http://www.jmknoble.net/software/x11-ssh-askpass/ home page] presents some [http://www.jmknoble.net/software/x11-ssh-askpass/screenshots.html 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.

* {{Pkg|ksshaskpass}} is available in the official repositories. It is dependent on {{Pkg|kdelibs}} and is suitable for the [[KDE]] Desktop Environment.

* {{Pkg|openssh-askpass}} depends on the {{Pkg|qt4}} libraries and is available from the official repositories.

===pam_ssh===
The [http://pam-ssh.sourceforge.net/ pam_ssh] project exists to provide a [[Wikipedia:Pluggable authentication module|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 {{AUR|pam_ssh}} package, available in the [[Arch User Repository]]. 

{{Note|pam_ssh 2.0 now requires that all private keys used in the authentication process be located under {{ic|~/.ssh/login-keys.d/}}.}}

Create a symlink to your private key file and place it in {{ic|~/.ssh/login-keys.d/}}.  Replace the {{ic|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 {{ic|/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.

{{Warning|Misconfiguring PAM can leave the system in a state where all users become locked out.  Before making any changes, you should have an understanding of how PAM configuration works as well as a backup means of accessing the PAM configuration files, such as an Arch Live CD, in case you become locked out and need to revert any changes.  An IBM developerWorks [http://www.ibm.com/developerworks/linux/library/l-pam/index.html article] is available which explains PAM configuration in further detail.}}

{{hc|/etc/pam.d/login|2=
#%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 {{ic|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 {{ic|~/.ssh/login-keys.d}} directory.  The {{ic|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 {{ic|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 {{ic|/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 {{ic|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|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.<br />
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 {{ic|StrictModes}} to {{ic|no}} in {{ic|sshd_config}}. If authentication with StrictModes off is successful, it is likely an issue with file permissions persists.
{{Tip|Do not forget to set {{ic|StrictModes}} to {{ic|yes}} for added security.}}
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, {{Pkg|kde-agent}} used to start ssh-agent on login, but since version 20140102-1 it got [https://projects.archlinux.org/svntogit/packages.git/commit/trunk?h=packages/kde-agent&id=1070467b0f74b2339ceca2b9471d1c4e2b9c9c8f 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:
{{bc|<nowiki>
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
</nowiki>}}

[[KDE#Plasma_5|Plasma 5]] を使用している場合、{{ic|~/.kde4}} ではなく {{ic|~/.config/plasma-workspace/}} ディレクトリにスクリプトを作成してください:
{{bc|<nowiki>
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
</nowiki>}}

==参照==
* [http://www.ibm.com/developerworks/linux/library/l-keyc.html OpenSSH key management, Part 1]
* [http://www.ibm.com/developerworks/linux/library/l-keyc2/ OpenSSH key management, Part 2]
* [http://www.ibm.com/developerworks/library/l-keyc3/ OpenSSH key management, Part 3]
* [http://kimmo.suominen.com/docs/ssh/ Getting started with SSH]
* [http://www.openssh.com/txt/release-5.7 OpenSSH 5.7 Release Notes]
* [https://stribika.github.io/2015/01/04/secure-secure-shell.html Secure Secure Shell]