code: function getk(params) {
    var k_buf = crypto
      .createHash(params.hash)
      .update(padToN(params.N, params))
      .update(padToN(params.g, params))
      .digest();
    return(new BigInteger(k_buf));
  }
docs: /*
  calculate the SRP-6 multiplier
  
  params:
  params (obj)     group parameters, with .N, .g, .hash
  
  returns: bignum