#include <iostream>
#ifdef GMP
#include <gmpxx.h>
#else
#include <NTL/ZZ.h>
using namespace NTL;
#endif
#include "sizes.h"

using namespace std;

int sharedsecret(
  unsigned char *s,unsigned long long *slen,
  const unsigned char *sk,unsigned long long sklen,
  const unsigned char *pk,unsigned long long pklen
)
{
  long long i;
  for (i = 0;i < SHAREDSECRET_BYTES;++i) s[i] = 0; *slen = SHAREDSECRET_BYTES;
#ifdef GMP
  mpz_class p;
  mpz_class a;
  mpz_class base;
  mpz_class result;
  mpz_import(a.get_mpz_t(),SECRETKEY_BYTES - PUBLICKEY_BYTES,-1,1,0,0,sk + PUBLICKEY_BYTES);
  mpz_import(base.get_mpz_t(),PUBLICKEY_BYTES,-1,1,0,0,pk);
  p = "106711310550942323238863446954494903303206603796265590798875260590060843568007841918927773348877395895791048832517368787533445258799160241834659776192282820736018472427221910874308833884006430888272214561307777629540843737689598751552666502301405808925850579645658786877473119117134988654123934303586903124139";
  mpz_powm(result.get_mpz_t(),base.get_mpz_t(),a.get_mpz_t(),p.get_mpz_t());
  if (mpz_sizeinbase(result.get_mpz_t(),256) > SHAREDSECRET_BYTES) return -1;
  mpz_export(s,0,-1,1,0,0,result.get_mpz_t());
#else
  ZZ a;
  ZZ p;
  ZZ base;
  ZZ result;
  base = ZZFromBytes(pk,PUBLICKEY_BYTES);
  a = ZZFromBytes(sk + PUBLICKEY_BYTES,SECRETKEY_BYTES - PUBLICKEY_BYTES);
  conv(p,"106711310550942323238863446954494903303206603796265590798875260590060843568007841918927773348877395895791048832517368787533445258799160241834659776192282820736018472427221910874308833884006430888272214561307777629540843737689598751552666502301405808925850579645658786877473119117134988654123934303586903124139");
  result = PowerMod(base,a,p);
  BytesFromZZ(s,result,SHAREDSECRET_BYTES);
#endif
  return 0;
}