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<title>RSA_private_encrypt</title>
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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="#return_values">RETURN VALUES</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>RSA_private_encrypt, RSA_public_decrypt - low-level signature operations</p>
<p>
</p>
<hr />
<h1><a name="synopsis">SYNOPSIS</a></h1>
<pre>
#include <openssl/rsa.h></pre>
<pre>
int RSA_private_encrypt(int flen, unsigned char *from,
unsigned char *to, RSA *rsa, int padding);</pre>
<pre>
int RSA_public_decrypt(int flen, unsigned char *from,
unsigned char *to, RSA *rsa, int padding);</pre>
<p>
</p>
<hr />
<h1><a name="description">DESCRIPTION</a></h1>
<p>These functions handle RSA signatures at a low-level.</p>
<p><code>RSA_private_encrypt()</code> signs the <strong>flen</strong> bytes at <strong>from</strong> (usually a
message digest with an algorithm identifier) using the private key
<strong>rsa</strong> and stores the signature in <strong>to</strong>. <strong>to</strong> must point to
<strong>RSA_size(rsa)</strong> bytes of memory.</p>
<p><strong>padding</strong> denotes one of the following modes:</p>
<dl>
<dt><strong><a name="rsa_pkcs1_padding" class="item">RSA_PKCS1_PADDING</a></strong></dt>
<dd>
<p>PKCS #1 v1.5 padding. This function does not handle the
<strong>algorithmIdentifier</strong> specified in PKCS #1. When generating or
verifying PKCS #1 signatures, <em>RSA_sign(3)</em> and <em>RSA_verify(3)</em> should be
used.</p>
</dd>
<dt><strong><a name="rsa_no_padding" class="item">RSA_NO_PADDING</a></strong></dt>
<dd>
<p>Raw RSA signature. This mode should <em>only</em> be used to implement
cryptographically sound padding modes in the application code.
Signing user data directly with RSA is insecure.</p>
</dd>
</dl>
<p><code>RSA_public_decrypt()</code> recovers the message digest from the <strong>flen</strong>
bytes long signature at <strong>from</strong> using the signer's public key
<strong>rsa</strong>. <strong>to</strong> must point to a memory section large enough to hold the
message digest (which is smaller than <strong>RSA_size(rsa) -
11</strong>). <strong>padding</strong> is the padding mode that was used to sign the data.</p>
<p>
</p>
<hr />
<h1><a name="return_values">RETURN VALUES</a></h1>
<p><code>RSA_private_encrypt()</code> returns the size of the signature (i.e.,
RSA_size(rsa)). <code>RSA_public_decrypt()</code> returns the size of the
recovered message digest.</p>
<p>On error, -1 is returned; the error codes can be
obtained by <em>ERR_get_error(3)</em>.</p>
<p>
</p>
<hr />
<h1><a name="see_also">SEE ALSO</a></h1>
<p><em>ERR_get_error(3)</em>,
<em>RSA_sign(3)</em>, <em>RSA_verify(3)</em></p>
<p>
</p>
<hr />
<h1><a name="copyright">COPYRIGHT</a></h1>
<p>Copyright 2000-2020 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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