When you are using OpenVPN official iOS App, OpenVPN Connect, you may seen this error massage
PolarSSL: error parsing config private key : PKCS5 - Requested encryption or digest alg not available
cd /etc/openvpn/easy-rsa
sudo ./easyrsa set-rsa-pass opvnuseropvnuser replace to the client's name you add
sudo cat pki/private/opvnuser.keyopvnuser replace to the client's name you add
Find the chapter which start at this header:
BEGIN RSA PRIVATE KEY
Copy entirely chapter, including header and footer.
Editing client configuration file
cd /home/pi/ovpns
sudo vim opvnuser.opvn opvnuser replace to the client's name you add
Paste the chapter which you copied after this footer, including header and footer
END ENCRYPTED PRIVATE KEY