android、ios客户端rsa加密秘钥生成

1、openssl生成公司钥对
openssl req -x509 -out public_key.der -outform der -new -newkey rsa:1024 -keyout private_key.pem

生成私钥：private_key.pem
公钥：public_key.der

2、将private_key.pem转换成PKCS8Padding格式
openssl pkcs8 -topk8 -inform PEM -in private_key.pem -outform PEM -nocrypt
返回一串字符如：
-----BEGIN PRIVATE KEY-----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-----END PRIVATE KEY-----
取出-----BEGIN PRIVATE KEY-----和-----END PRIVATE KEY-----之间的字符保存，做为解密的私钥串。

3、将生成的公钥DER文件BASE64编码
openssl base64 -in public_key.der
生成的字符串做为IOS的公钥

4、从已有的私钥中，导出android使用的公钥
openssl rsa -in private_key.pem -pubout -out rsa_public_key.pem