openssl
OpenSSL> genrsa -out app_private_key.pem 2048  # 私钥
OpenSSL> rsa -in app_private_key.pem -pubout -out app_public_key.pem # 导出公钥
OpenSSL> exit

app_private_key_string.pem

-----BEGIN RSA PRIVATE KEY-----
         私钥内容
-----END RSA PRIVATE KEY-----


alipay_public_key_string.pem

-----BEGIN PUBLIC KEY-----
         公钥内容
-----END PUBLIC KEY-----