according to the manpage of stunnel4
the certificates in this directory should be named XXXXXXXX.0 where XXXXXXXX is the hash value of the DER encoded subject of the cert (the first 4 bytes of the MD5 hash in least significant byte order).
How can I produce a such thing ?
I tried, unsuccessfully :s :
openssl x509 -in cert.crt -inform PEM -out cert.der -outform DER
then
openssl dgst cert.der