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<title>Cryptographic transforms.: XML Security Library Reference Manual</title>
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<div class="sect1">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="xmlsec-notes-new-crypto-transforms"></a>Cryptographic transforms.</h2></div></div></div>
<p>The cryptographic transforms (digests, signatures and encryption)
implementation is the main goal of "xmlsec-<crypto>" library.
Most of the cryptographic <a class="link" href="xmlsec-notes-transforms.html" title="Transforms and transforms chain.">transforms</a>
use default <em class="structfield"><code>pushBin</code></em> and <em class="structfield"><code>popBin</code></em>
methods and provide custom <a class="link" href="xmlsec-transforms.html#xmlSecTransformExecuteMethod" title="xmlSecTransformExecuteMethod ()">execute</a> method.
The binary transform <a class="link" href="xmlsec-transforms.html#xmlSecTransformExecuteMethod" title="xmlSecTransformExecuteMethod ()">execute</a> method
processes data from the input buffer
<em class="structfield"><code>inBuf</code></em> and pushes results to
<em class="structfield"><code>outBuf</code></em>. The transform should try to
consume and remove data from <em class="structfield"><code>inBuf</code></em> buffer
as soon as the data became available. However, it might happen
that current data size in the input buffer is not enough (for example,
RSA-PKCS1 algorithm requires that all the data are available in
one buffer). In this case, transform might keep the data in the
input buffer till the next call to
<a class="link" href="xmlsec-transforms.html#xmlSecTransformExecuteMethod" title="xmlSecTransformExecuteMethod ()">execute</a>
method. The "last" parameter of the
<a class="link" href="xmlsec-transforms.html#xmlSecTransformExecuteMethod" title="xmlSecTransformExecuteMethod ()">execute</a>
indicates that transform MUST process all the data in the input buffer
and return as much as possible in the output buffer. The
<a class="link" href="xmlsec-transforms.html#xmlSecTransformExecuteMethod" title="xmlSecTransformExecuteMethod ()">execute</a> method
might be called multiple times with non-zero "last" parameter until
the transforms returns nothing
in the output buffer. In addition, the transform implementation is
responsible for managing the transform <em class="structfield"><code>status</code></em>
variable.
</p>
<div class="table">
<a name="id-1.2.14.5.2.13"></a><p class="title"><b>Table 2. Typical transform status managing.</b></p>
<div class="table-contents"><table class="table" summary="Typical transform status managing." border="1">
<colgroup>
<col>
<col>
</colgroup>
<tbody>
<tr>
<td>xmlSecTransformStatusNone</td>
<td>Transform initializes itself (for example, cipher transform
generates or reads IV) and sets <em class="structfield"><code>status</code></em>
variable to xmlSecTransformStatusWorking.</td>
</tr>
<tr>
<td>xmlSecTransformStatusWorking</td>
<td>Transform process the next (if "last" parameter is zero) or
last block of data (if "last" parameter is non-zero).
When transform returns all the data, it sets the
<em class="structfield"><code>status</code></em> variable to
xmlSecTransformStatusFinished.</td>
</tr>
<tr>
<td>xmlSecTransformStatusFinished</td>
<td>Transform returns no data to indicate that it finished
processing.</td>
</tr>
</tbody>
</table></div>
</div>
<p><br class="table-break">
</p>
<p>In adition to <a class="link" href="xmlsec-transforms.html#xmlSecTransformExecuteMethod" title="xmlSecTransformExecuteMethod ()">execute</a>
methods, signature, hmac or digest transforms
MUST implement <a class="link" href="xmlsec-transforms.html#xmlSecTransformVerifyMethod" title="xmlSecTransformVerifyMethod ()">verify</a> method.
The <a class="link" href="xmlsec-transforms.html#xmlSecTransformVerifyMethod" title="xmlSecTransformVerifyMethod ()">verify</a> method is called
after transform execution is finished. The
<a class="link" href="xmlsec-transforms.html#xmlSecTransformVerifyMethod" title="xmlSecTransformVerifyMethod ()">verify</a> method implementation
must set the "status" member to <a class="link" href="xmlsec-transforms.html#xmlSecTransformStatusOk">xmlSecTransformStatusOk</a>
if signature, hmac or digest is successfully verified or to
<a class="link" href="xmlsec-transforms.html#xmlSecTransformStatusFail">xmlSecTransformStatusFail</a>
otherwise.
</p>
<p>The transforms that require a key (signature or encryption
transforms, for example) MUST imlpement
<a class="link" href="xmlsec-transforms.html#xmlSecTransformSetKeyRequirementsMethod" title="xmlSecTransformSetKeyRequirementsMethod ()">setKeyReq</a>
(prepares the <a class="link" href="xmlsec-keys.html#xmlSecKeyReq" title="struct xmlSecKeyReq">key requirements</a>
for key search) and
<a class="link" href="xmlsec-transforms.html#xmlSecTransformSetKeyMethod" title="xmlSecTransformSetKeyMethod ()">setKey</a>
(sets the key in the transform) methods.
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