nd() must be called before returning from the function. If <b>ctx</b> is NULL, nothing is done. When BN_CTX_end() is called, the <b>BIGNUM</b> pointers obtained from BN_CTX_get() become invalid.</p>

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

<p>BN_CTX_start() and BN_CTX_end() return no values.</p>

<p>BN_CTX_get() returns a pointer to the <b>BIGNUM</b>, or <b>NULL</b> on error. Once BN_CTX_get() has failed, the subsequent calls will return <b>NULL</b> as well, so it is sufficient to check the return value 