These certificates form a very long chain, used to test the
MBEDTLS_X509_MAX_INT_CA limit.

NN.key is the private key of certificate NN.crt.

The root is 00.crt and N+1.crt is a child of N.crt.

File cNN.pem contains the chain NN.crt to 00.crt.

Those certificates were generated by tests/data_files/dir-maxpath/long.sh.