生成私钥：genrsa -out rsa_private_key.pem 1024
生成公钥：rsa -in rsa_private_key.pem -out rsa_public_key.pem -pubout
PKCS8：pkcs8 -topk8 -in rsa_private_key.pem -out pkcs8_rsa_private_key.pem -nocrypt
出处：http://blog.csdn.net/chaijunkun/article/details/7275632/
