.. _gfpecpublickey:


GFpECPublicKey
==============


Computes a public key from the given private key of the elliptic curve
cryptosystem over GF(p).


Syntax
------


IppStatus ippsGFpECPublicKey(const IppsBigNumState\* pPrivate,
IppsGFpECPoint\* pPublic, IppsGFpECState\* pEC, Ipp8u\* pScratchBuffer);


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


``ippcp.h``


Parameters
----------


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   :header-rows: 0

   * - pPrivate   
     - Pointer to the private key ``privKey``.
   * - pPublic   
     - Pointer to the public key ``pubKey``.
   * - pEC   
     - Pointer to the context of the elliptic curve.
   * - pScratchBuffer   
     - Pointer to the scratch buffer.




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


The function computes the public key ``pubKey`` from the given private
key ``privKey`` of the elliptic cryptosystem over a finite field
GF(``p``).


The private key ``privKey`` is a number that lies in the range of [1,
``n``-1] where ``n`` is the order of the elliptic curve base point. The
public key ``pubKey`` is an elliptic curve point such that ``pubKey`` =
``privKey`` · ``G``, where ``G`` is the base point of the elliptic
curve.


The private key ``privKey`` can be generated by the function
`GFpECPrivateKey <gfpecprivatekey-gfpecpublickey-gfpectstkeypair.html>`__.


The context of the point ``pubKey`` as an elliptic curve point must be
created by using the functions
`GFpECPointGetSize <gfpecpointgetsize.html>`__
and `GFpECPointInit <gfpecpointinit.html>`__.


The elliptic curve domain parameters must be defined by the functions:
`GFpECInitStd <gfpecinitstd.html>`__,
`GFpECInit <gfpecinit.html>`__,
`GFpECSet <gfpecset.html>`__, or
`GFpECSetSubgroup <gfpecsetsubgroup.html>`__.


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


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   :header-rows: 0

   * - ippStsNoErr   
     - Indicates no error. Any other value indicates an error or warning.
   * - ippStsNullPtrErr   
     - Indicates an error condition if any of the specified pointers is NULL.
   * - ippStsContextMatchErr   
     - Indicates an error condition if any of the contexts pointed to by pPrivate, pPublic, or pEC does not match the operation.
   * - ippStsIvalidPrivateKey   
     - Indicates an error condition if the value of the private key falls outside the range of [1, ``n``-1].
   * - ippStsRangeErr   
     - Indicates an error condition if pPublic does not belong to the finite field that the elliptic curve is initialized over.