生成私鑰，設定e=65537 ,也可以不加引數，預設就是65537
（私鑰檔案編碼是PKCS#1格式）

openssl genrsa -65537 -out rsa_private_key.pem 2048
Generating RSA private key, 2048 bit long modulus
e is 65537 (0x10001)

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根據私鑰生成公鑰

openssl rsa -in rsa_private_key.pem -out rsa_public_key.pem -pubout

writing RSA key

如果私鑰檔案編碼需要轉成PKCS#8格式

openssl pkcs8 -topk8 -in rsa_private_key.pem -out pkcs8_rsa_private_key.pem -nocrypt