/*************************************************
* Prime Generation Source File                   *
* (C) 1999-2006 The Botan Project                *
*************************************************/

#include <botan/numthry.h>
#include <botan/lookup.h>
#include <botan/bit_ops.h>
#include <botan/parsing.h>
#include <botan/rng.h>
#include <botan/ui.h>
#include <algorithm>
#include <memory>

namespace Botan {

namespace {

/*************************************************
* Increment the seed by one                      *
*************************************************/
void increment(SecureVector<byte>& seed)
   {
   for(u32bit j = seed.size(); j > 0; --j)
      if(++seed[j-1])
         break;
   }

}

/*************************************************
* Attempt DSA prime generation with given seed   *
*************************************************/
bool generate_dsa_primes(BigInt& p, BigInt& q, const byte const_seed[],
                         u32bit seed_len, u32bit pbits, u32bit counter_start)
   {
   if(seed_len < 20)
      throw Invalid_Argument("DSA prime generation needs a seed "
                             "at least 160 bits long");
   if((pbits % 64 != 0) || (pbits > 1024) || (pbits < 512))
      throw Invalid_Argument("DSA prime generation algorithm does not support "
                             "prime size " + to_string(pbits));

   std::auto_ptr<HashFunction> sha1(get_hash("SHA-1"));

   SecureVector<byte> seed(const_seed, seed_len);

   SecureVector<byte> qhash = sha1->process(seed);
   increment(seed);
   SecureVector<byte> qhash2 = sha1->process(seed);
   xor_buf(qhash, qhash2, qhash.size());

   qhash[0] |= 0x80;
   qhash[19] |= 0x01;
   q.binary_decode(qhash, qhash.size());
   if(!is_prime(q))
      return false;
   UI::pulse(UI::PRIME_FOUND);

   u32bit n = (pbits-1) / 160, b = (pbits-1) % 160;
   SecureVector<byte> W(20 * (n+1));
   BigInt X;

   for(u32bit j = 0; j != counter_start; ++j)
      for(u32bit k = 0; k != n + 1; ++k)
         increment(seed);

   for(u32bit j = 0; j != 4096 - counter_start; ++j)
      {
      UI::pulse(UI::PRIME_SEARCHING);

      for(u32bit k = 0; k != n + 1; ++k)
         {
         increment(seed);
         sha1->update(seed);
         sha1->final(W + 20 * (n-k));
         }
      X.binary_decode(W + (20 - 1 - b/8), W.size() - (20 - 1 - b/8));
      X.set_bit(pbits-1);

      p = X - (X % (2*q) - 1);

      if(p.bits() == pbits && is_prime(p))
         {
         UI::pulse(UI::PRIME_FOUND);
         return true;
         }
      }
   return false;
   }

/*************************************************
* Generate DSA Primes                            *
*************************************************/
SecureVector<byte> generate_dsa_primes(BigInt& p, BigInt& q, u32bit pbits)
   {
   SecureVector<byte> seed(20);

   while(true)
      {
      Global_RNG::randomize(seed, seed.size());
      UI::pulse(UI::PRIME_SEARCHING);
      if(generate_dsa_primes(p, q, seed, seed.size(), pbits))
         return seed;
      }
   }

/*************************************************
* Generate a random prime                        *
*************************************************/
BigInt random_prime(u32bit bits, const BigInt& coprime,
                    u32bit equiv, u32bit modulo)
   {
   if(bits <= 48)
      throw Invalid_Argument("random_prime: Can't make a prime of " +
                             to_string(bits) + " bits");

   if(coprime <= 0)
      throw Invalid_Argument("random_prime: coprime must be > 0");
   if(modulo % 2 == 1 || modulo == 0)
      throw Invalid_Argument("random_prime: Invalid modulo value");
   if(equiv >= modulo || equiv % 2 == 0)
      throw Invalid_Argument("random_prime: equiv must be < modulo, and odd");

   while(true)
      {
      UI::pulse(UI::PRIME_SEARCHING);

      BigInt p = random_integer(bits);
      p.set_bit(bits - 2);
      p.set_bit(0);

      if(p % modulo != equiv)
         p += (modulo - p % modulo) + equiv;

      const u32bit sieve_size = std::min(bits / 2, PRIME_TABLE_SIZE);
      SecureVector<u32bit> sieve(sieve_size);

      for(u32bit j = 0; j != sieve.size(); ++j)
         {
         sieve[j] = p % PRIMES[j];
         UI::pulse(UI::PRIME_SIEVING);
         }

      u32bit counter = 0;
      while(true)
         {
         if(counter == 4096 || p.bits() > bits)
            break;

         UI::pulse(UI::PRIME_SEARCHING);

         bool passes_sieve = true;
         ++counter;
         p += modulo;

         for(u32bit j = 0; j != sieve.size(); ++j)
            {
            sieve[j] = (sieve[j] + modulo) % PRIMES[j];
            UI::pulse(UI::PRIME_SIEVING);
            if(sieve[j] == 0)
               passes_sieve = false;
            }

         if(!passes_sieve || gcd(p - 1, coprime) != 1)
            continue;
         UI::pulse(UI::PRIME_PASSED_SIEVE);
         if(passes_mr_tests(p))
            {
            UI::pulse(UI::PRIME_FOUND);
            return p;
            }
         }
      }
   }

}