ERROR: public key for cuda-libs7.5.18-3.el7.nux.x86_64.rpm is not installed

Hi, there.

I tried to install cuda on centos 7.6 by the command “yum install cuda”.
I followed all the guidance in http://developer.download.nvidia.com/compute/cuda/9.0/Prod/docs/sidebar/CUDA_Installation_Guide_Linux.pdf
There was no comment for Importing key this guidance on centos.
The only thing about the public key is in the ubuntu part.

But there was an error “public key for cuda-libs7.5.18-3.el7.nux.x86_64.rpm is not installed”
Downloading packages:
warning: /var/cache/yum/x86_64/7/li.nux.ro_download_numx_desktop_el7_x86_64/packages/cuda-libs-7.5.18-3.el7.nux.x86_64.rpm: Header V4 RSA/SHA1 Signature, key ID 85c6cd8a: NOKEY

Please give me any bits of advice.

Thanks!