Tu trouveras pas mal de réponses par ici :
http://forum.hardware.fr/hfr/resea [...] et_2_1.htm
Oui tu peux, cf. l'extrait du man d'openvpn ci-dessous :
--cipher alg
Encrypt packets with cipher algorithm alg. The default is BF-CBC, an abbreviation for Blowfish in Cipher Block Chaining mode. Blowfish has the advantages of being fast, very secure, and allowing key sizes of up to 448 bits. Blowfish is designed to be used in situations where keys are changed infrequently.
For more information on blowfish, see http://www.counterpane.com/blowfish.html
To see other ciphers that are available with OpenVPN, use the --show-ciphers option.
OpenVPN supports the CBC, CFB, and OFB cipher modes.
Set alg=none to disable encryption.