公私钥
//生成私钥(公私钥格式参见 RFC3447)
openssl genrsa -out private.pem
//从私钥中提取出公钥
openssl rsa -in private.pem -pubout -out public.pem
//加密文件
openssl rsautl -encrypt -in hello.txt -inkey public.pem -pubin -out hello.en
//解密文件
openssl rsautl -decrypt -in hello.en -inkey private.pem -out hello.de