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<ul>
<li><a href="#name">NAME</a></li>
<li><a href="#synopsis">SYNOPSIS</a></li>
<li><a href="#description">DESCRIPTION</a></li>
<li><a href="#notes">NOTES</a></li>
<li><a href="#return_values">RETURN VALUES</a></li>
<li><a href="#bugs">BUGS</a></li>
<li><a href="#see_also">SEE ALSO</a></li>
<li><a href="#copyright">COPYRIGHT</a></li>
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<h1><a name="name">NAME</a></h1>
<p>CMS_decrypt - decrypt content from a CMS envelopedData structure</p>
<p>
</p>
<hr />
<h1><a name="synopsis">SYNOPSIS</a></h1>
<pre>
#include <openssl/cms.h></pre>
<pre>
int CMS_decrypt(CMS_ContentInfo *cms, EVP_PKEY *pkey, X509 *cert,
BIO *dcont, BIO *out, unsigned int flags);</pre>
<p>
</p>
<hr />
<h1><a name="description">DESCRIPTION</a></h1>
<p><code>CMS_decrypt()</code> extracts and decrypts the content from a CMS EnvelopedData
structure. <strong>pkey</strong> is the private key of the recipient, <strong>cert</strong> is the
recipient's certificate, <strong>out</strong> is a BIO to write the content to and
<strong>flags</strong> is an optional set of flags.</p>
<p>The <strong>dcont</strong> parameter is used in the rare case where the encrypted content
is detached. It will normally be set to NULL.</p>
<p>
</p>
<hr />
<h1><a name="notes">NOTES</a></h1>
<p>Although the recipients certificate is not needed to decrypt the data it is
needed to locate the appropriate (of possible several) recipients in the CMS
structure.</p>
<p>If <strong>cert</strong> is set to NULL all possible recipients are tried. This case however
is problematic. To thwart the MMA attack (Bleichenbacher's attack on
PKCS #1 v1.5 RSA padding) all recipients are tried whether they succeed or
not. If no recipient succeeds then a random symmetric key is used to decrypt
the content: this will typically output garbage and may (but is not guaranteed
to) ultimately return a padding error only. If <code>CMS_decrypt()</code> just returned an
error when all recipient encrypted keys failed to decrypt an attacker could
use this in a timing attack. If the special flag <strong>CMS_DEBUG_DECRYPT</strong> is set
then the above behaviour is modified and an error <strong>is</strong> returned if no
recipient encrypted key can be decrypted <strong>without</strong> generating a random
content encryption key. Applications should use this flag with
<strong>extreme caution</strong> especially in automated gateways as it can leave them
open to attack.</p>
<p>It is possible to determine the correct recipient key by other means (for
example looking them up in a database) and setting them in the CMS structure
in advance using the CMS utility functions such as CMS_set1_pkey(). In this
case both <strong>cert</strong> and <strong>pkey</strong> should be set to NULL.</p>
<p>To process KEKRecipientInfo types CMS_set1_key() or CMS_RecipientInfo_set0_key()
and <code>CMS_RecipientInfo_decrypt()</code> should be called before <code>CMS_decrypt()</code> and
<strong>cert</strong> and <strong>pkey</strong> set to NULL.</p>
<p>The following flags can be passed in the <strong>flags</strong> parameter.</p>
<p>If the <strong>CMS_TEXT</strong> flag is set MIME headers for type <strong>text/plain</strong> are deleted
from the content. If the content is not of type <strong>text/plain</strong> then an error is
returned.</p>
<p>
</p>
<hr />
<h1><a name="return_values">RETURN VALUES</a></h1>
<p><code>CMS_decrypt()</code> returns either 1 for success or 0 for failure.
The error can be obtained from <code>ERR_get_error(3)</code></p>
<p>
</p>
<hr />
<h1><a name="bugs">BUGS</a></h1>
<p>The lack of single pass processing and the need to hold all data in memory as
mentioned in <code>CMS_verify()</code> also applies to <code>CMS_decrypt()</code>.</p>
<p>
</p>
<hr />
<h1><a name="see_also">SEE ALSO</a></h1>
<p><em>ERR_get_error(3)</em>, <em>CMS_encrypt(3)</em></p>
<p>
</p>
<hr />
<h1><a name="copyright">COPYRIGHT</a></h1>
<p>Copyright 2008-2016 The OpenSSL Project Authors. All Rights Reserved.</p>
<p>Licensed under the OpenSSL license (the "License"). You may not use
this file except in compliance with the License. You can obtain a copy
in the file LICENSE in the source distribution or at
<a href="https://www.openssl.org/source/license.html">https://www.openssl.org/source/license.html</a>.</p>
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