dhlib.c

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#include <stdio.h>
#include <openssl/bn.h>
#include <fcntl.h>
#include <string.h>

#include "prime.h"

static int primesInit = 0;
static BIGNUM *g,*n;

char *uRandStr(int len)
{
  char tmpStr[5000];
  int ur;
  int rc;
  int i;
  
  unsigned char c;
  
  
  
  if ( (len > 2048) || (len < 128))
    return(NULL);
  
  ur = open("/dev/urandom",O_RDONLY);

  if (ur < 0)
    return(NULL);

  // get a random char and make sure the high bit is set
  while(1)
  {
    rc = read(ur,&c,1);
    if (rc != 1)
    {
      close(ur);
      return(NULL);
    }
    
    
    if (c & 0x80)
      break;
  }

  
  memset(tmpStr,0,5000);
  i=0;

  sprintf(&tmpStr[i],"%02x",c);
  for(i=2;i<len*2;i+=2)
  {
    rc = read(ur,&c,1);
    if (rc != 1)
    {
      close(ur);
      return(NULL);
    }
    sprintf(&tmpStr[i],"%02x",c);
  }
  close(ur);
  
  return(strdup(tmpStr));
      
}

//  int BN_mod_exp(BIGNUM *r, BIGNUM *a, const BIGNUM *p,
//       const BIGNUM *m, BN_CTX *ctx);

static int initPrimes()
{
  static int inited=0;
  int        rc;
  
  if (inited)
    return(0);
  
  inited=1;
  
  rc = BN_hex2bn(&g,gP);
  rc = BN_hex2bn(&n,nP);
}

int computeKey(BIGNUM **k,BIGNUM *X,BIGNUM *x)
{
  BIGNUM *kTmp = *k;
  BN_CTX *ctx;
  int rc;

  initPrimes();
  
  ctx = BN_CTX_new();
  rc = BN_mod_exp(*k,X,x,n,ctx);
  BN_CTX_free(ctx);
  return(rc);
  
}

int getDHX(BIGNUM **resultX,BIGNUM **secretX)
{
  BN_CTX *ctx;
  char *randNum;
  BIGNUM *x,*X;
  
  int  rc;

  X = *resultX;
  x = *secretX;

  initPrimes();

  // alice
  randNum = uRandStr(128);   // get a 
  if (randNum == NULL)
  {
    fprintf(stderr,"urandStr failed\n");
    return(-2);
  }
  rc = BN_hex2bn(&x,randNum);
  X = BN_new();

  ctx = BN_CTX_new();
  rc = BN_mod_exp(X,g,x,n,ctx);
  BN_CTX_free(ctx);

//  pNum = BN_bn2hex(X);
//  secretNum = BN_bn2hex(x);  

//  *secretX = x;
//  *resultX = X;
  return(0);
  
  
  
}