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<title>DH_generate_parameters</title>
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<ul id="index">
 <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="#HISTORY">HISTORY</a></li>
 <li><a href="#COPYRIGHT">COPYRIGHT</a></li>
</ul>

DH_generate_parameters_ex, DH_generate_parameters, DH_check, DH_check_params, DH_check_ex, DH_check_params_ex, DH_check_pub_key_ex - generate and check Diffie-Hellman parameters

<h1 id="SYNOPSIS">SYNOPSIS</h1>

<pre><code> #include &lt;openssl/dh.h&gt;

int DH_generate_parameters_ex(DH *dh, int prime_len, int generator, BN_GENCB *cb);

int DH_check(DH *dh, int *codes);
 int DH_check_params(DH *dh, int *codes);

int DH_check_ex(const DH *dh);
 int DH_check_params_ex(const DH *dh);
 int DH_check_pub_key_ex(const DH *dh, const BIGNUM *pub_key);</code></pre>

Deprecated:

<pre><code> #if OPENSSL_API_COMPAT &lt; 0x00908000L
 DH *DH_generate_parameters(int prime_len, int generator,
 void (*callback)(int, int, void *), void *cb_arg);
 #endif</code></pre>

<h1 id="DESCRIPTION">DESCRIPTION</h1>

DH_generate_parameters_ex() generates Diffie-Hellman parameters that can be shared among a group of users, and stores them in the provided DH structure. The pseudo-random number generator must be seeded before calling it. The parameters generated by DH_generate_parameters_ex() should not be used in signature schemes.

prime_len is the length in bits of the safe prime to be generated. generator is a small number &gt; 1, typically 2 or 5.

A callback function may be used to provide feedback about the progress of the key generation. If cb is not NULL, it will be called as described in <a href="../man3/BN_generate_prime.html">BN_generate_prime(3)</a> while a random prime number is generated, and when a prime has been found, BN_GENCB_call(cb, 3, 0) is called. See <a href="../man3/BN_generate_prime_ex.html">BN_generate_prime_ex(3)</a> for information on the BN_GENCB_call() function.

DH_generate_parameters() is similar to DH_generate_prime_ex() but expects an old-style callback function; see <a href="../man3/BN_generate_prime.html">BN_generate_prime(3)</a> for information on the old-style callback.

DH_check_params() confirms that the p and g are likely enough to be valid. This is a lightweight check, if a more thorough check is needed, use DH_check(). The value of *codes is updated with any problems found. If *codes is zero then no problems were found, otherwise the following bits may be set:

<dl>

<dt id="DH_CHECK_P_NOT_PRIME">DH_CHECK_P_NOT_PRIME</dt>
<dd>

The parameter p has been determined to not being an odd prime. Note that the lack of this bit doesn&#39;t guarantee that p is a prime.

</dd>
<dt id="DH_NOT_SUITABLE_GENERATOR">DH_NOT_SUITABLE_GENERATOR</dt>
<dd>

The generator g is not suitable. Note that the lack of this bit doesn&#39;t guarantee that g is suitable, unless p is known to be a strong prime.

</dd>
<dt id="DH_MODULUS_TOO_LARGE">DH_MODULUS_TOO_LARGE</dt>
<dd>

The modulus is too large.

</dd>
</dl>

DH_check() confirms that the Diffie-Hellman parameters dh are valid. The value of *codes is updated with any problems found. If *codes is zero then no problems were found, otherwise the following bits may be set:

<dl>

<dt id="DH_CHECK_P_NOT_PRIME1">DH_CHECK_P_NOT_PRIME</dt>
<dd>

The parameter p is not prime.

</dd>
<dt id="DH_CHECK_P_NOT_SAFE_PRIME">DH_CHECK_P_NOT_SAFE_PRIME</dt>
<dd>

The parameter p is not a safe prime and no q value is present.

</dd>
<dt id="DH_UNABLE_TO_CHECK_GENERATOR">DH_UNABLE_TO_CHECK_GENERATOR</dt>
<dd>

The generator g cannot be checked for suitability.

</dd>
<dt id="DH_NOT_SUITABLE_GENERATOR1">DH_NOT_SUITABLE_GENERATOR</dt>
<dd>

The generator g is not suitable.

</dd>
<dt id="DH_CHECK_Q_NOT_PRIME">DH_CHECK_Q_NOT_PRIME</dt>
<dd>

The parameter q is not prime.

</dd>
<dt id="DH_CHECK_INVALID_Q_VALUE">DH_CHECK_INVALID_Q_VALUE</dt>
<dd>

The parameter q is invalid.

</dd>
<dt id="DH_CHECK_INVALID_J_VALUE">DH_CHECK_INVALID_J_VALUE</dt>
<dd>

The parameter j is invalid.

</dd>
</dl>

DH_check_ex(), DH_check_params() and DH_check_pub_key_ex() are similar to DH_check() and DH_check_params() respectively, but the error reasons are added to the thread&#39;s error queue instead of provided as return values from the function.

<h1 id="RETURN-VALUES">RETURN VALUES</h1>

DH_generate_parameters_ex(), DH_check() and DH_check_params() return 1 if the check could be performed, 0 otherwise.

DH_generate_parameters() returns a pointer to the DH structure or NULL if the parameter generation fails.

DH_check_ex(), DH_check_params() and DH_check_pub_key_ex() return 1 if the check is successful, 0 for failed.

The error codes can be obtained by <a href="../man3/ERR_get_error.html">ERR_get_error(3)</a>.

<a href="../man3/DH_new.html">DH_new(3)</a>, <a href="../man3/ERR_get_error.html">ERR_get_error(3)</a>, <a href="../man3/RAND_bytes.html">RAND_bytes(3)</a>, <a href="../man3/DH_free.html">DH_free(3)</a>

<h1 id="HISTORY">HISTORY</h1>

DH_generate_parameters() was deprecated in OpenSSL 0.9.8; use DH_generate_parameters_ex() instead.

<h1 id="COPYRIGHT">COPYRIGHT</h1>

Licensed under the OpenSSL license (the &quot;License&quot;). 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>.

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