title: Access BIGNUM bits in OpenSSL 1.1?
body: <p>Prior 1.1 version of OpenSSL API I had access to raw representation of BIGNUM types through "d" field in struct bignum_st:</p>
  
  <pre><code>   struct bignum_st
             {
             BN_ULONG *d;    /* Pointer to an array of 'BN_BITS2' bit chunks. */
             int top;        /* Index of last used d +1. */
             /* The next are internal book keeping for bn_expand. */
             int dmax;       /* Size of the d array. */
             int neg;        /* one if the number is negative */
             int flags;
             };
  </code></pre>
  
  <p>In my program I need to get lowest byte from BIGNUM after some computations - it is quite easily - simply as:</p>
  
  <pre><code>(bn-&gt;d[0] &amp; 0xff)
  </code></pre>
  
  <p>With API of OpenSSL version 1.1 many BN internals have been made opaque - I cannot get direct access to representation of BIGNUM. I still can get raw representation, but with additional copying - either <code>BN_bn2bin</code> or <code>BN_mask_bits</code>.</p>
  
  <p>There is any way to access lowest byte without extra copying?</p>