.. _gfpecverifysm2:


GFpECVerifySM2
==============


Verifies authenticity of a digital signature over a message digest using
the SM2 scheme.


Syntax
------


IppStatus ippsGFpECVerifySM2(const IppsBigNumState\* pMsgDigest, const
IppsGFpECPoint\* pRegPublic, const IppsBigNumState\* pSignR, const
IppsBigNumState\* pSignS, IppECResult\* pResult, IppsGFpECState\* pEC,
Ipp8u\* pScratchBuffer);


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


``ippcp.h``


Parameters
----------


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

   * -     pMsgDigest   
     -  Pointer to the message digest *msg*.
   * -     pRegPublic   
     -  Pointer to the signer's regular public key.
   * -     pSignR   
     -  Pointer to the integer ``r`` of the digital signature.
   * -     pSignS   
     -  Pointer to the integer ``s`` of the digital signature.
   * -     pResult   
     -  Pointer to the digital signature verification result.
   * -     pEC   
     -  Pointer to the context of the elliptic curve.
   * -     pScratchBuffer   
     -  Pointer to the scratch buffer.




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


The function verifies authenticity of the digital signature, represented
as integer big numbers ``r`` and ``s``, over a message digest *msg*. The
digital signature over the message digest *msg* must be computed using
the SM2 scheme
[`SM2 <bibliography.html>`__] by to the
`GFpECSignSM2 <gfpecsignsm2.html>`__
function.


You can get the message sender's regular public key ``regPubKey`` by
calling the function
`GFpECPublicKey <gfpecpublickey.html>`__.


The result of the digital signature verification can take one of these
values:


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

   * -     ippECValid   
     -  Digital signature is valid.
   * -     ippECInvalidSignature   
     -  Digital signature is not valid.




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


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 any of the specified pointers is NULL.
   * -     ippStsContextMatchErr   
     -  Indicates an error condition if any of the contexts pointed to by pMsgDigest, pRegPublic, pSignR, pSignS, or pEC does not match the operation.
   * -     ippStsMessageErr   
     -  Indicates an error condition if the value of ``msg`` pointed to by pMsgDigest falls outside the range of [1, ``n``-1], where ``n`` is the order of the elliptic curve base point ``G``.
   * -     ippStsRangeErr   
     -  Indicates an error condition if any of the parameters pointed to by pSignR or pSignS is negative.
   * -     ippStsOutOfRangeErr   
     -  Indicates an error condition if the public key point does not belong to the finite field over which the elliptic curve is initialized.
   * -     ippStsNotSupportedModeErr   
     -  Indicates an error condition if the finite field GFp under the elliptic curve is not prime.