text: #ifndef _VRF_H
  #define _VRF_H
  
  /*
   * Copyright (c) 2018, Henry Corrigan-Gibbs
   * 
   * Permission to use, copy, modify, and/or distribute this software for any
   * purpose with or without fee is hereby granted, provided that the above
   * copyright notice and this permission notice appear in all copies.
   * 
   * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
   * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
   * FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
   * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
   * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
   * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
   * PERFORMANCE OF THIS SOFTWARE.
   */
  
  #include <openssl/ec.h>
  #include "params.h"
  #include "ddh.h"
  
  #ifdef __cplusplus
  extern "C"{
  #endif
  
  struct vrf_proof {
    EC_POINT *val_pt;     /* Point corresponding to output value. */
    DDHProof ddh_proof;   /* DDH proof. */
  };
  
  typedef struct vrf_proof *VRFProof;
  typedef const struct vrf_proof *const_VRFProof;
  
  VRFProof VRFProof_new(const_Params params);
  void VRFProof_free(VRFProof proof);
  
  /* Verify using pk that val was derived from input. */
  int VRF_verify (const_Params params,
      const EC_POINT *pk, const uint8_t *input, int inputlen,
      const BIGNUM *val, const_VRFProof proof);
  
  #ifdef __cplusplus
  }
  #endif
  #endif
  
  