Server certificate verification failed

When I use "sudo apt update " to update my nvidia driver, I got this error message.

Err http://developer.download.nvidia.com Packages
server certificate verification failed. CAfile: /etc/ssl/certs/ca-certificates.crt CRLfile: none
W: Failed to fetch http://developer.download.nvidia.com/compute/cuda/repos/ubuntu1404/x86_64/Packages server certificate verification failed. CAfile: /etc/ssl/certs/ca-certificates.crt CRLfile: none
W: Failed to fetch http://developer.download.nvidia.com/compute/machine-learning/repos/ubuntu1404/x86_64/Packages server certificate verification failed. CAfile: /etc/ssl/certs/ca-certificates.crt CRLfile: none

I tried to use “export GIT_SSL_NO_VERIFY=1” but the error still exists.

Anyone can help? Where can I get the certificate?