<?xml version="1.0" encoding="utf-8" standalone="yes"?><html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Ciphering</title>
<meta content="text/html; charset=utf-8" http-equiv="Content-Type" />
<meta content="text/css" http-equiv="Content-Style-Type" />
<script src="NED?action=retrieve&amp;identifier=dn00188761&amp;edition=1&amp;language=none&amp;coverage=global&amp;encoding=javascript&amp;component=data&amp;item=data" type="text/javascript" xml:space="preserve">
</script>
<?conversion name="Pub2XHTML" version="2.0" source="urn:mars:dn0430556:1:en:global:publishing_online_1_0:data:data:*:*:*" date="2005-02-21T15:04:44Z"?>
<link href="NED?action=retrieve&amp;identifier=dn01158124&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=css&amp;component=data&amp;item=data" rel="stylesheet" title="Nokia Networks default online style" type="text/css" />
<meta content="draft" name="status" />
<?conversion name="SplitHTML" version="1.9" source="urn:mars:dn0430556:1:en:global:publishing_online_1_0:data:data:39:*:*" date="2005-02-21T15:04:44Z"?>
</head>
<body lang="en" xml:lang="en">
<p><a name="ned_top" shape="rect"></a>
<a name="ned_1" shape="rect"></a></p>

<a name="jan1751351122" shape="rect"></a>
<a name="p2xhtm-repid-1" shape="rect"></a>
<table width="100%">
<tr>
<td align="center" colspan="1" rowspan="1" width="20%"><?NED5 annotation?>
<br clear="none" /><?NED5 printview?>
</td>
<td align="center" colspan="1" rowspan="1" width="20%"></td>
<td align="center" colspan="1" rowspan="1" width="20%"></td>
<td align="center" colspan="1" rowspan="1" width="20%"></td>
<td align="center" colspan="1" rowspan="1" width="20%"><a href="NED?action=retrieve&amp;identifier=dn0430556_about&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=xhtml_1_0&amp;component=data&amp;item=data&amp;pointer=ned_top#ned_top" onclick="openSmallPopup(event,'NED?action=retrieve&amp;identifier=dn0430556_about&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=xhtml_1_0&amp;component=data&amp;item=data&amp;pointer=ned_top#ned_top');return false" shape="rect" target="_blank"><img alt="Document information" border="0" class="Metainfo" src="NED?action=retrieve&amp;identifier=dn01158003&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=gif&amp;component=data&amp;item=data" /></a></td>
</tr>
</table>


<div class="div">
<h1>Ciphering</h1>

<p>Ciphering is one of the security procedures defined to
protect subscriber identity and data. When Ciphering is active, all information
exchanged between the mobile and the network on the dedicated radio channels
is encrypted. The key previously set between the network and the MS is used
to encipher and to decipher the encrypted information. During the authentication
procedure in which the identity provided by the MS is checked to prevent unauthorised
use, the ciphering key Kc is set between the network and the MS. The ciphering
key must be stored in the BSC for assigning a new channel because the same
key is used for one transaction.</p>


<p>The feature enables the usage of different A5 algorithms
(currently A5/1 and A5/2) and gives an alternative of using no ciphering at
all (A5/0). A5/2 allows ciphering to be used in some market areas as in some
areas the use of A5/1 is forbidden. User cannot set the ciphering mode. MSC
has although the possibility to indicate to BSS all ciphering algorithms.
A selection of the ciphering algorithm to be used is based on a BSS level
system parameter, which determines the allowed algorithms and their fixed
preference. The operator is not able to change the reference, which currently
is A5/1 first, then A5/2, and A5/0 at the last. For the BTS three different
software packages will be available: A5/1,2,0 packet, A5/2,0 packet, and A5/0
packet. In the BSC ciphering method must specified in the software package
in the customer specific data.</p>


<p>The following assumptions have been made:</p>


<ol class="type-odd">
<li type="1"><p>One ciphering algorithm in the network
at a time is supported, that is, multiple ciphering is not supported.</p>
</li>
<li type="1"><p>The A5/1 phase 1 network does not check
the spare bits. See ETR 09.90.</p>
</li>
<li type="1"><p>The phase 1 MS is not disturbed upon
receiving an unknown RR message.</p>
</li>
</ol>


<a name="feb26415562324" shape="rect"></a>
<div>
<table border="1">
<thead>
<tr align="left" char="" charoff="50" valign="bottom">
<th colspan="1" rowspan="1" valign="top"><p>MS</p>
</th>
<th colspan="1" rowspan="1" valign="top"><p>Ciphering used</p>
</th>
<th colspan="1" rowspan="1" valign="top"><p>Network</p>
</th>
<th colspan="1" rowspan="1" valign="top"><p>Case</p>
</th>
</tr>
</thead>
<tbody>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p>A5/1</p>
</td>
<td colspan="1" rowspan="1"><p>A5/1</p>
</td>
<td colspan="1" rowspan="1"><p>A5/1</p>
</td>
<td colspan="1" rowspan="1"><p>1.</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p>A5/1</p>
</td>
<td colspan="1" rowspan="1"><p>no ciphering</p>
</td>
<td colspan="1" rowspan="1"><p>no ciphering</p>
</td>
<td colspan="1" rowspan="1"><p>2a.</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p>A5/1</p>
</td>
<td colspan="1" rowspan="1"><p>Connection released</p>
</td>
<td colspan="1" rowspan="1"><p>no ciphering</p>
</td>
<td colspan="1" rowspan="1"><p>2b.</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p>A5/1, A5/2</p>
</td>
<td colspan="1" rowspan="1"><p>A5/1</p>
</td>
<td colspan="1" rowspan="1"><p>A5/1</p>
</td>
<td colspan="1" rowspan="1"><p>3.</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p>A5/2</p>
</td>
<td colspan="1" rowspan="1"><p>A5/2</p>
</td>
<td colspan="1" rowspan="1"><p>A5/2</p>
</td>
<td colspan="1" rowspan="1"><p>4.</p>
</td>
</tr>
</tbody>
</table>
</div>


<p>Case 1: Call is established normally according to phase
1.</p>


<p>Case 2a: If no ciphering is available in the network, the
call is established without ciphering. Decision of this is made by the MSC,
and the ciphering procedure is initiated towards the BSC.</p>


<p>Case 2b: The network (MSC) tries to use A5/1 ciphering
even when the BSS (the BSC or BTS) does not support encryption (if disabled).
In this case, the end result is that the call is released.</p>


<p>Case 3: The network ignores the A5/2 capability of the
MS and continues the call establishment including ciphering with A5/1 which
should also be supported by the MS.</p>


<p>Case 4: Call is established normally including ciphering
with A5/2.</p>
</div>
</body>
</html>