.. _gfpecsetsubgroup:


GFpECSetSubgroup
================


Sets up the parameters defining an elliptic curve points subgroup.


Syntax
------


IppStatus ippsGFpECSetSubGroup(const IppsGFpElement\* pX, const
IppsGFpElement\* pY, const IppsBigNumState\* pOrder, const
IppsBigNumState\* pCofactor, IppsGFpECState\* pEC);


Include Files
-------------


``ippcp.h``


Parameters
----------


.. list-table:: 
   :header-rows: 0

   * - pX, pY   
     - Pointers to the ``X`` and ``Y`` coordinates of the base point of the elliptic curve.
   * - pOrder    
     - Pointer to the big number context storing the order of the base point.
   * - pCofactor   
     - Pointer to the big number context storing the cofactor.
   * - pEC   
     - Pointer to the context of the elliptic curve.




Description
-----------


This function sets up an elliptic curve as the subgroup generated by the
base point over the finite field.


.. note::


   Only the ``pEC`` parameter is required. You can omit the other parameters
   by setting their values to NULL or zero.


Return Values
-------------


.. list-table:: 
   :header-rows: 0

   * - ippStsNoErr   
     - Indicates no error. Any other value indicates an error or warning.
   * - ippStsNullPtrErr   
     - Indicates an error condition if pEC is NULL.
   * - ippStsContextMatchErr   
     - Indicates an error condition in the following cases:
       
       * ``IppsGFpECState`` context parameter does not match the operation.
       * Any of the pointers to elliptic curve parameters is not zero and the context parameter does not match the operation.
       
   * - ippStsBadArgErr   
     - Indicates an error condition if any of the specified IppsBigNumState contexts defines zero or a negative number.
   * - ippStsOutOfRangeErr   
     - Indicates an error if the base point coordinates (pX, pY) do not belong to the finite field over which the elliptic curve is initialized.
   * - ippStsRangeErr   
     - Indicates an error condition in the following cases:
       
       * The size of the base point order exceeds the maximal size of the order for the given curve.
       * The bit size of the cofactor exceeds the bit size of the element of the finite field over which the elliptic curve is initialized.