Granting permissions to certificates

How to grant permission to NETWORK SERVICE to a certificate:

C:\Program Files\Windows Resource Kits\Tools>winhttpcertcfg.exe -g -c LOCAL_MACHINE\My -s subjectstring -a NetworkService
Microsoft (R) WinHTTP Certificate Configuration ToolCopyright (C) Microsoft Corporation 2001.
Matching certificate:
CN=
OU=
O=
L=
C=
Granting private key access for account: NT AUTHORITY\NETWORK SERVICE