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<html>
<head>
  <meta name="generator" content=
  "HTML Tidy for Linux/x86 (vers 6 November 2007), see www.w3.org">

  <title>Using MD5 for Authentication</title>
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<body class="SECT1" bgcolor="#FFFFFF" text="#000000" link="#0000FF"
vlink="#840084" alink="#0000FF">
  <div class="NAVHEADER">
    <table summary="Header navigation table" width="100%" border=
    "0" cellpadding="0" cellspacing="0">
      <tr>
        <th colspan="3" align="center">LPRng Reference Manual: 24
        Sep 2004 (For LPRng-3.8.28)</th>
      </tr>

      <tr>
        <td width="10%" align="left" valign="bottom"><a href=
        "x9495.htm" accesskey="P">Prev</a></td>

        <td width="80%" align="center" valign="bottom">Chapter 17.
        Permissions and Authentication</td>

        <td width="10%" align="right" valign="bottom"><a href=
        "x9639.htm" accesskey="N">Next</a></td>
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  <div class="SECT1">
    <h1 class="SECT1"><a name="AEN9572" id="AEN9572">17.16. Using
    MD5 for Authentication</a></h1>

    <p><b class="APPLICATION">LPRng</b> has built-in support for
    using MD5 digests as an authentication method. The
    implementation is provided as an example of how to add user
    level authentication into the <b class="APPLICATION">LPRng</b>
    system.</p>

    <p>The method used to do authentication is very simple. Each
    user has a file containing a set of keys that are used to salt
    an md5 hash. The information being transferred has its md5
    checksum calculated using this salt, and is then transferred to
    the destination, along with the md5 hash result. At the
    destination the server will get the user id, obtain the salt
    value from a key file, and then calculate the md5 hash value.
    If the two are in agreement, authentication is successful.</p>

    <p>The keyfile used for md5 authentication contains an id
    followed by a text string whose binary value is used as a hash
    key:</p>

    <div class="INFORMALEXAMPLE">
      <a name="AEN9579" id="AEN9579"></a>
      <pre class="SCREEN">
id1=key
id2=key

Example:

lpr@h2=tadf79asd%^1asdf
lpr@h1=fdfa%$^&amp;^%$
</pre>
    </div>

    <div class="SECT2">
      <h2 class="SECT2"><a name="AEN9581" id="AEN9581">17.16.1.
      Printcap Entries</a></h2>

      <p>Options used:</p>

      <ul>
        <li>
          <p><tt class="LITERAL">auth=md5</tt><span class=
          "emphasis"><i class="EMPHASIS">use MD5
          authentication</i></span></p>
        </li>

        <li>
          <p><tt class="LITERAL">auth_forward=md5</tt><span class=
          "emphasis"><i class="EMPHASIS">forward using MD5
          authentication</i></span></p>
        </li>

        <li>
          <p><tt class="LITERAL">md5_id=</tt><span class=
          "emphasis"><i class="EMPHASIS">id for
          server</i></span></p>
        </li>

        <li>
          <p><tt class="LITERAL">md5_forward_id=</tt><span class=
          "emphasis"><i class="EMPHASIS">id for
          server</i></span></p>
        </li>

        <li>
          <p><tt class=
          "LITERAL">md5_server_keyfile=</tt><span class=
          "emphasis"><i class="EMPHASIS">server
          keyfile</i></span></p>
        </li>
      </ul>

      <p>Example printcap entry:</p>

      <div class="INFORMALEXAMPLE">
        <a name="AEN9606" id="AEN9606"></a>
        <pre class="SCREEN">
pr:
    :lp=pr@wayoff
    :auth=md5
    :md5_id=lpr@wayoff.com
pr:server
    :auth_forward=md5
    :md5_id=lpr@wayoff.com
    :md5_server_keyfile
    :md5_forward_id=lpr@faroff.com
</pre>
      </div>

      <p>The <tt class="LITERAL">md5_id</tt> value is used by the
      client to obtain a hash key that is used to salt the md5
      calculation for client to server transfers. The <tt class=
      "LITERAL">md5_forward_id</tt> value is used by the server to
      obtain a hash key that is used to salt the md5 calculation
      for server to server transfers.</p>

      <p>The <tt class="LITERAL">md5_server_keyfile</tt> contains
      the keys of users; the id sent as the connection information
      is used to obtain the key from the file.</p>

      <p>To set up md5 authentication, all that is needed is the
      following.</p>

      <ul>
        <li>
          <p>For each user generate a key and place it in the
          server keyfile. This file should have the form:</p>

          <div class="INFORMALEXAMPLE">
            <a name="AEN9617" id="AEN9617"></a>
            <pre class="SCREEN">
user1@host1=asdfasdfadf
user2@host2=a8789087asddasdf
</pre>
          </div>
        </li>

        <li>
          <p>Assign a key to the server, and set its printcap entry
          to this key.</p>

          <div class="INFORMALEXAMPLE">
            <a name="AEN9621" id="AEN9621"></a>
            <pre class="SCREEN">
pr:
    :lp=pr@wayoff
    :auth=md5
    :md5_id=lpr@wayoff.com
</pre>
          </div>
        </li>

        <li>
          <p>For each user, create a user key file with the
          following format:</p>

          <div class="INFORMALEXAMPLE">
            <a name="AEN9625" id="AEN9625"></a>
            <pre class="SCREEN">
lpr@wayoff = user1@host1 asdfasdfadf
</pre>
          </div>The first entry corresponds to the <tt class=
          "LITERAL">md5_id</tt> value in the printcap. The second
          field is the <acronym class="ACRONYM">AUTHUSER</acronym>
          value supplied to the server and which will be used to
          look up the key in the servers key file. Finally, the
          last field is the salt value for the md5 calculation.
        </li>
      </ul>
    </div>

    <div class="SECT2">
      <h2 class="SECT2"><a name="AEN9629" id="AEN9629">17.16.2.
      User Environment Variables and Files</a></h2>

      <p>Options used:</p>

      <ul>
        <li>
          <p><tt class="LITERAL">MD5KEYFILE=5</tt><span class=
          "emphasis"><i class="EMPHASIS">location of user
          keyfile</i></span></p>
        </li>
      </ul>

      <p>The <tt class="LITERAL">MD5KEYFILE</tt> environment
      variable contains the path to the user keytab file.</p>
    </div>
  </div>

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        <td width="33%" align="left" valign="top">Using SSL for
        Authentication</td>

        <td width="34%" align="center" valign="top"><a href=
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