The RPC_SECURITY_DESCRIPTOR structure represents the RPC security descriptors.

 typedef struct _RPC_SECURITY_DESCRIPTOR {
   [size_is(cbInSecurityDescriptor), length_is(cbOutSecurityDescriptor)] 
     PBYTE lpSecurityDescriptor;
   DWORD cbInSecurityDescriptor;
   DWORD cbOutSecurityDescriptor;
 } RPC_SECURITY_DESCRIPTOR,
  *PRPC_SECURITY_DESCRIPTOR;

lpSecurityDescriptor: A buffer that contains a SECURITY_DESCRIPTOR, as specified in [MS-DTYP] section 2.4.6.

cbInSecurityDescriptor: The size in bytes of the security descriptor.

cbOutSecurityDescriptor: The size in bytes of the security descriptor.