Download the 5 certificates into a temporary directory (i.e. /tmp), use names as specified here.
Use the right mouse key to click the links, from the context menu choose “Save as”.
telekom.crt
https://pki.pca.dfn.de/fh-schmalkalden-ca/pub/cacert/rootcert.crt
dfn.crt
https://pki.pca.dfn.de/fh-schmalkalden-ca/pub/cacert/intermediatecacert.crt
hsm-ca.crt
https://pki.pca.dfn.de/fh-schmalkalden-ca/pub/cacert/cacert.crt
iukca3.crt
zefica.crt
Run
openssl x509 -inform der -in telekom.crt -out telekom.pem openssl x509 -inform der -in dfn.crt -out dfn.pem openssl x509 -inform der -in hsm-ca.crt -out hsm-ca.pem cp iukca3.crt iukca3.pem cp zefica.crt zefica.pem
to convert or copy the files to PEM file format.
yum -y install ca-certificates
update-ca-trust force-enable
update-ca-trust
update-ca-trust
update-ca-certificates