Carries out the GCM authenticated decryption operation using the key 
set up by an earlier call to GCM_InitKey.
Public Declare Function GCM_NextDecrypt Lib "diCryptoSys.dll" (ByVal hContext As Long, ByRef lpOutput As Byte, ByVal nOutLen As Long, 
ByRef lpData As Byte, ByVal nDataLen As Long, ByRef lpIV As Byte, ByVal nIvLen As Long, ByRef lpAAD As Byte, ByVal nAadLen As Long, 
ByRef lpTag As Byte, ByVal nTagLen As Long) As Long
nRet = GCM_NextDecrypt(hContext, lpOutput(0), nOutLen, abData(0), nDataLen, 
abIV(0), nIvLen, abAAD(0), nAadLen, abTag(0), nTagLen)
long __stdcall  GCM_NextDecrypt(long hContext, unsigned char *lpOutput, long nOutLen, const unsigned char *lpData, long nDataLen, const unsigned char *lpIV, long nIvLen, const unsigned char *lpAAD, long nAadLen, const unsigned char *lpTag, long nTagLen);
If successful, the return value is 0; otherwise it returns a non-zero error code.
See the remarks for GCM_Decrypt and the 
Security considerations for AEAD encryption.