#use wml::openssl-macros area=docs page=BN_mod_inverse

<title>Documents, BN_mod_inverse(3)</title>

<h1>BN_mod_inverse(3)</h1>

#use wml::imp::generic

{:
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	<LI><A HREF="#NAME">NAME</A>
	<LI><A HREF="#SYNOPSIS">SYNOPSIS</A>
	<LI><A HREF="#DESCRIPTION">DESCRIPTION</A>
	<LI><A HREF="#RETURN_VALUES">RETURN VALUES</A>
	<LI><A HREF="#SEE_ALSO">SEE ALSO</A>
	<LI><A HREF="#HISTORY">HISTORY</A>
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<H1><A NAME="NAME">NAME</A></H1>
<P>
BN_mod_inverse - compute inverse modulo n

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<H1><A NAME="SYNOPSIS">SYNOPSIS</A></H1>
<PRE> #include &lt;openssl/bn.h&gt;
</PRE>
<PRE> BIGNUM *BN_mod_inverse(BIGNUM *r, BIGNUM *a, const BIGNUM *n,
           BN_CTX *ctx);
</PRE>
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<H1><A NAME="DESCRIPTION">DESCRIPTION</A></H1>
<P>
<CODE>BN_mod_inverse()</CODE> computes the inverse of <STRONG>a</STRONG> modulo <STRONG>n</STRONG>
places the result in <STRONG>r</STRONG> (<CODE>(a*r)%n==1</CODE>). If <STRONG>r</STRONG> is NULL, a new <STRONG>BIGNUM</STRONG> is created.

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<P>
<STRONG>ctx</STRONG> is a previously allocated <STRONG>BN_CTX</STRONG> used for temporary variables. <STRONG>r</STRONG> may be the same <STRONG>BIGNUM</STRONG> as <STRONG>a</STRONG> or <STRONG>n</STRONG>.

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<H1><A NAME="RETURN_VALUES">RETURN VALUES</A></H1>
<P>
<CODE>BN_mod_inverse()</CODE> returns the <STRONG>BIGNUM</STRONG> containing the inverse, and NULL on error. The error codes can be obtained
by <A HREF="../crypto/ERR_get_error.html#">ERR_get_error(3)</A>.

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<H1><A NAME="SEE_ALSO">SEE ALSO</A></H1>
<P>
<A HREF="../crypto/bn.html#">bn(3)</A>, <A HREF="../crypto/ERR_get_error.html#">ERR_get_error(3)</A>, <A HREF="../crypto/BN_add.html#">BN_add(3)</A>



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<H1><A NAME="HISTORY">HISTORY</A></H1>
<P>
<CODE>BN_mod_inverse()</CODE> is available in all versions of SSLeay and
OpenSSL.

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:}