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<erlref>
  <header>
    <copyright>
      <year>2018</year><year>2018</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      Licensed under the Apache License, Version 2.0 (the "License");
      you may not use this file except in compliance with the License.
      You may obtain a copy of the License at
      
      http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      See the License for the specific language governing permissions and
      limitations under the License.

    </legalnotice>
    
    <title>ssh_file</title>
    <prepared></prepared>
    <docno></docno>
    <date></date>
    <rev></rev>
  </header>
  <module since="OTP 21.2">ssh_file</module>
  <modulesummary>Default callback module for the client's and server's database operations in the ssh application</modulesummary>
  <description>
    <p>This module is the default callback handler for the client's and the server's user and host "database" operations.
    All data, for instance key pairs, are stored in files in the normal file system. This page documents the files, where they
    are stored and configuration options for this callback module.
    </p>
    <p>The intention is to be compatible with the
    <url href="http://www.openssh.com">OpenSSH</url>
    storage in files. Therefore it mimics directories and filenames of
    <url href="http://www.openssh.com">OpenSSH</url>.
    </p>

    <p>Ssh_file implements the <seealso marker="ssh:ssh_server_key_api">ssh_server_key_api</seealso> and
    the <seealso marker="ssh:ssh_client_key_api">ssh_client_key_api</seealso>.
    This enables the user to make an own interface using for example a database handler.
    </p>
    <p>Such another callback module could be used by setting the option
    <seealso marker="ssh:ssh#type-key_cb_common_option"><c>key_cb</c></seealso>
    when starting a client or a server (with for example
    <seealso marker="ssh:ssh#connect-3">ssh:connect</seealso>,
    <seealso marker="ssh:ssh#daemon-2">ssh:daemon</seealso> of
    <seealso marker="ssh:ssh#shell-1">ssh:shell</seealso>
    ).
    </p>

    <note>
      <p>The functions are <i>Callbacks</i> for the SSH app. They are not intended to be called from the user's code!
      </p>
    </note>
  </description>

  <section>
    <title>Files, directories and who uses them</title>
    <section>
      <title>Daemons</title>
      <p>Daemons uses all files stored in the <seealso marker="#SYSDIR">SYSDIR</seealso> directory.
      </p>
      <p>Optionaly, in case of <c>publickey</c> authorization, one or more of the remote user's public keys
      in the <seealso marker="#USERDIR">USERDIR</seealso> directory are used.
      See the files 
      <seealso marker="#USERDIR-authorized_keys"><c>USERDIR/authorized_keys</c></seealso> and
      <seealso marker="#USERDIR-authorized_keys2"><c>USERDIR/authorized_keys2</c></seealso>.
      </p>
    </section>

    <section>
      <title>Clients</title>
      <p>Clients uses all files stored in the <seealso marker="#USERDIR">USERDIR</seealso> directory.
      </p>
    </section>

    <section>
      <title>Directory contents</title>
      <taglist>
	<tag><marker id="LOCALUSER"/>LOCALUSER</tag>
	<item><p>The user name of the OS process running the Erlang virtual machine (emulator).</p>
	</item>

	<tag><marker id="SYSDIR"/>SYSDIR</tag>
	<item><p>This is the directory holding the server's files:</p>
	<list>
	  <item><marker id="SYSDIR-ssh_host_dsa_key"/><c>ssh_host_dsa_key</c> - private dss host key (optional)</item>
	  <item><marker id="SYSDIR-ssh_host_rsa_key"/><c>ssh_host_rsa_key</c> - private rsa host key (optional)</item>
	  <item><marker id="SYSDIR-ssh_host_ecdsa_key"/><c>ssh_host_ecdsa_key</c> - private ecdsa host key (optional)</item>
	  <item><marker id="SYSDIR-ssh_host_ed25519_key"/><c>ssh_host_ed25519_key</c> - private eddsa host key for curve 25519 (optional)</item>
	  <item><marker id="SYSDIR-ssh_host_ed448_key"/><c>ssh_host_ed448_key</c> - private eddsa host key for curve 448 (optional)</item>
	</list>
	<p>At least one host key must be defined. The default value of SYSDIR is <marker id="#/etc/ssh"/><c>/etc/ssh</c>.
	</p>
	<p>For security reasons, this directory is normally accessible only to the root user.
	</p>
	<p>To change the SYSDIR, see the <seealso marker="#type-system_dir_daemon_option">system_dir</seealso> option.
	</p>
	</item>

	<tag><marker id="USERDIR"/>USERDIR</tag>
	<item><p>This is the directory holding the files:</p>
	<list>
	  <item><marker id="USERDIR-authorized_keys"/><c>authorized_keys</c>
	  and, as second alternative
	  <marker id="USERDIR-authorized_keys2"/><c>authorized_keys2</c> - 
	  the user's public keys are stored concatenated in one of those files.
	  </item>
	  <item><marker id="USERDIR-known_hosts"/><c>known_hosts</c> - host keys from hosts visited
	  concatenated. The file is created and used by the client.</item>
	  <item><marker id="USERDIR-id_dsa"/><c>id_dsa</c> - private dss user key (optional)</item>
	  <item><marker id="USERDIR-id_rsa"/><c>id_rsa</c> - private rsa user key (optional)</item>
	  <item><marker id="USERDIR-id_ecdsa"/><c>id_ecdsa</c> - private ecdsa user key (optional)</item>
	  <item><marker id="USERDIR-id_ed25519"/><c>id_ed25519</c> - private eddsa user key for curve 25519 (optional)</item>
	  <item><marker id="USERDIR-id_ed448"/><c>id_ed448</c> - private eddsa user key for curve 448 (optional)</item>
	</list>
	<p>The default value of USERDIR is <c>/home/</c><seealso marker="#LOCALUSER"><c>LOCALUSER</c></seealso><c>/.ssh</c>.
	</p>
	<p>To change the USERDIR, see the <seealso marker="#type-user_dir_common_option">user_dir</seealso> option
	</p>
	</item>
      </taglist>
    </section>
  </section>

  <datatypes>
    <datatype_title>Options for the default ssh_file callback module</datatype_title>
    <datatype>
      <name name="user_dir_common_option"/>
      <desc>
	<p>Sets the <seealso marker="#USERDIR">user directory</seealso>.</p>
      </desc>
    </datatype>

    <datatype>
      <name name="user_dir_fun_common_option"/>
      <name name="user2dir"/>
      <desc>
	<p>Sets the <seealso marker="#USERDIR">user directory</seealso> dynamically
	by evaluating the <c>user2dir</c> function.
	</p>
      </desc>
    </datatype>

    <datatype>
      <name name="system_dir_daemon_option"/>
      <desc>
        <p>Sets the <seealso marker="#SYSDIR">system directory</seealso>.</p>
      </desc>
    </datatype>

    <datatype>
      <name name="pubkey_passphrase_client_options"/>
      <desc>
	<p>If the user's DSA, RSA or ECDSA key is protected by a passphrase, it can be
	supplied with thoose options.
	</p>
	<p>Note that EdDSA passhrases (Curves 25519 and 448) are not implemented.</p>
      </desc>
    </datatype>

  </datatypes>

  <funcs>
    <func>
      <name since="OTP 21.2">host_key(Algorithm, DaemonOptions) -> {ok, Key} | {error, Reason}</name>
      <fsummary></fsummary>
      <desc>
	<p><strong>Types and description</strong></p>
	<p>See the api description in
	<seealso marker="ssh:ssh_server_key_api#Module:host_key-2">ssh_server_key_api, Module:host_key/2</seealso>.
	</p>
	<p><strong>Options</strong></p>
	<list>
	  <item><seealso marker="#type-system_dir_daemon_option">system_dir</seealso></item>
	  <!-- item>dsa_pass_phrase</item -->
	  <!-- item>rsa_pass_phrase</item -->
	  <!-- item>ecdsa_pass_phrase</item -->
	</list>
	<p><strong>Files</strong></p>
	<list>
	  <item><seealso marker="#SYSDIR-ssh_host_rsa_key"><c>SYSDIR/ssh_host_rsa_key</c></seealso></item>
	  <item><seealso marker="#SYSDIR-ssh_host_dsa_key"><c>SYSDIR/ssh_host_dsa_key</c></seealso></item>
	  <item><seealso marker="#SYSDIR-ssh_host_ecdsa_key"><c>SYSDIR/ssh_host_ecdsa_key</c></seealso></item>
          <item><seealso marker="#SYSDIR-ssh_host_ed25519_key"><c>SYSDIR/ssh_host_ed25519_key</c></seealso></item>
          <item><seealso marker="#SYSDIR-ssh_host_ed448_key"><c>SYSDIR/ssh_host_ed448_key</c>c></seealso></item>
	</list>
      </desc>
    </func>

    <func>
      <name since="OTP 21.2">is_auth_key(PublicUserKey, User, DaemonOptions) -> Result</name>
      <fsummary></fsummary>
      <desc>
	<p><strong>Types and description</strong></p>
	<p>See the api description in
	<seealso marker="ssh:ssh_server_key_api#Module:is_auth_key-3">ssh_server_key_api: Module:is_auth_key/3</seealso>.
	</p>
	<p><strong>Options</strong></p>
	<list>
	  <item><seealso marker="#type-user_dir_fun_common_option">user_dir_fun</seealso></item>
	  <item><seealso marker="#type-user_dir_common_option">user_dir</seealso></item>
	</list>
	<p><strong>Files</strong></p>
	<list>
	  <item><seealso marker="#USERDIR-authorized_keys"><c>USERDIR/authorized_keys</c></seealso></item>
	  <item><seealso marker="#USERDIR-authorized_keys2"><c>USERDIR/authorized_keys2</c></seealso></item>
	</list>
      </desc>
    </func>

    <func>
      <name since="OTP 21.2">add_host_key(HostNames, PublicHostKey, ConnectOptions) -> ok | {error, Reason}</name>
      <fsummary></fsummary>
      <desc>
	<p><strong>Types and description</strong></p>
	<p>See the api description in
	<seealso marker="ssh:ssh_client_key_api#Module:add_host_key-3">ssh_client_key_api, Module:add_host_key/3</seealso>.
	</p>
	<p><strong>Option</strong></p>
	<list>
	  <item><seealso marker="#type-user_dir_common_option">user_dir</seealso></item>
	</list>
	<p><strong>File</strong></p>
	<list>
	  <item><seealso marker="#USERDIR-known_hosts"><c>USERDIR/known_hosts</c></seealso></item>
	</list>
      </desc>
    </func>

    <func>
      <name since="OTP 21.2">is_host_key(Key, Host, Algorithm, ConnectOptions) -> Result</name>
      <fsummary></fsummary>
      <desc>
	<p><strong>Types and description</strong></p>
	<p>See the api description in
	<seealso marker="ssh:ssh_client_key_api#Module:is_host_key-4">ssh_client_key_api, Module:is_host_key/4</seealso>.
	</p>
	<p><strong>Option</strong></p>
	<list>
	  <item><seealso marker="#type-user_dir_common_option">user_dir</seealso></item>
	</list>
	<p><strong>File</strong></p>
	<list>
	  <item><seealso marker="#USERDIR-known_hosts"><c>USERDIR/known_hosts</c></seealso></item>
	</list>
      </desc>
    </func>

    <func>
      <name since="OTP 21.2">user_key(Algorithm, ConnectOptions) -> {ok, PrivateKey} | {error, Reason}</name>
      <fsummary></fsummary>
      <desc>
	<p><strong>Types and description</strong></p>
	<p>See the api description in
	<seealso marker="ssh:ssh_client_key_api#Module:user_key-2">ssh_client_key_api, Module:user_key/2</seealso>.
	</p>
	<p><strong>Options</strong></p>
	<list>
	  <item><seealso marker="#type-user_dir_common_option">user_dir</seealso></item>
	  <item><seealso marker="#type-pubkey_passphrase_client_options">dsa_pass_phrase</seealso></item>
	  <item><seealso marker="#type-pubkey_passphrase_client_options">rsa_pass_phrase</seealso></item>
	  <item><seealso marker="#type-pubkey_passphrase_client_options">ecdsa_pass_phrase</seealso></item>
	</list>
	<p>Note that EdDSA passhrases (Curves 25519 and 448) are not implemented.</p>
	<p><strong>Files</strong></p>
	<list>
	  <item><seealso marker="#USERDIR-id_dsa"><c>USERDIR/id_dsa</c></seealso></item>
	  <item><seealso marker="#USERDIR-id_rsa"><c>USERDIR/id_rsa</c></seealso></item>
	  <item><seealso marker="#USERDIR-id_ecdsa"><c>USERDIR/id_ecdsa</c></seealso></item>
	  <item><seealso marker="#USERDIR-id_ed25519"><c>USERDIR/id_ed25519</c></seealso></item>
	  <item><seealso marker="#USERDIR-id_ed448"><c>USERDIR/id_ed448</c></seealso></item>
	</list>
      </desc>
    </func>

  </funcs>

</erlref>
