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rsa_san.cpp in RSA_file_encryption.

			
#include "stdafx.h"
// This is a slow but easy RSA encryption class
// By sanicle,2005.12 
// 3mn@3mn.net

#include "stdio.h"
#include "rsa_san.h"

class Prime_factory_san
{
  unsigned np;
  unsigned *pl;
  public:
  Prime_factory_san();
  ~Prime_factory_san();
  vlong find_prime( vlong & start );
};

// prime factory implementation

static int is_probable_prime_san( const vlong &p )
{
  // Test based on Fermats theorem a**(p-1) = 1 mod p for prime p
  // For 1000 bit numbers this can take quite a while
  const rep = 4;
  const unsigned any[rep] = { 2,3,5,7 };
  for ( unsigned i=0; i<rep; i+=1 )
    if ( modexp( any[i], p-vlong(1), p ) != vlong(1) )
      return 0;
  return 1;
}

Prime_factory_san::Prime_factory_san()
{
  np = 0;
  unsigned NP = 200;
  pl = new unsigned[NP];

  // Initialise pl
  unsigned SS = 8*NP; // Rough estimate to fill pl
  char * b = new char[SS+1]; // one extra to stop search
  for (unsigned i=0;i<=SS;i+=1) b[i] = 1;
  unsigned p = 2;
  while (1)
  {
    // skip composites
    while ( b[p] == 0 ) p += 1;
    if ( p == SS ) break;
    pl[np] = p;
    np += 1;
    if ( np == NP ) break;
    // cross off multiples
    unsigned c = p*2;
    while ( c < SS )
    {
      b[c] = 0;
      c += p;
    }
    p += 1;
  }
  delete [] b;
}

Prime_factory_san::~Prime_factory_san()
{
  delete [] pl;
}

vlong Prime_factory_san::find_prime( vlong & start )
{
  unsigned SS = 1000; // should be enough unless we are unlucky
  char * b = new char[SS]; // bitset of candidate primes
  unsigned tested = 0;
  while (1)
  {
    unsigned i;
    for (i=0;i<SS;i++)
      b[i] = 1;
    for (i=0;i<np;i++)
    {
      unsigned p = pl[i];
      unsigned r = start % vlong(p); // not as fast as it should be - could do with special routine
      if (r) r = p - r;
      // cross off multiples of p
      while ( r < SS )
      {
        b[r] = 0;
        r += p;
      }
    }
    // now test candidates
    for (i=0;i<SS;i++)
    {
   			

			...
			...
			... to be continued.

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