注：因为Crypto这个项目已经放弃了更新，安装Crypto需要pip install pycryptodome

import Crypto
from Crypto.Hash import MD5
from Crypto.PublicKey import RSA
# 计算签名
from Crypto.Signature import PKCS1_v1_5
# 计算加密解密
from Crypto.Cipher import PKCS1_v1_5 as Cipher_pkcs1_v1_5
from base64 import b64decode, b64encode


class RsaUtil(object):

    def sign_encrypt(self, message, private_key):
        """ RSA私钥加密 MD5withRSA """
        # digest = SHA.new()
        digest = MD5.new()
        digest.update(message.encode(encoding='utf8'))
        private_key = RSA.importKey(b64decode(private_key))
        signer = PKCS1_v1_5.new(private_key)
        sig = b64encode(signer.sign(digest))
        return sig.decode('utf8')

    def get_max_length(self, rsa_key, encrypt=True):
        """加密内容过长时 需要分段加密 换算每一段的长度.
            :param rsa_key: 钥匙.
            :param encrypt: 是否是加密.
        """
        blocksize = Crypto.Util.number.size(rsa_key.n) / 8
        reserve_size = 11  # 预留位为11
        if not encrypt:  # 解密时不需要考虑预留位
            reserve_size = 0
        maxlength = blocksize - reserve_size
        return maxlength

    def long_rsa_public_encrypt(self, msg, public_key):
        """ 分段使用公钥加密
        单次加密串的长度最大为(key_size / 8 - 11)
        加密的 plaintext 最大长度是 证书key位数 / 8 - 11, 例如1024 bit的证书，被加密的串最长 1024 / 8 - 11=117,
        解决办法是分块加密，然后分块解密就行了，
        因为 证书key固定的情况下，加密出来的串长度是固定的。
        """
        # base64加密后 再进行RSA加密，也可以选择直接进行RSA加密，这个看业务要求
        msg = b64encode(msg.encode('utf-8'))
        
        length = len(msg)
        public_key = RSA.importKey(b64decode(public_key))
        max_length = int(self.get_max_length(public_key))
        pub_obj = Cipher_pkcs1_v1_5.new(public_key)
        # 长度不用分段
        if length < max_length:
            return b64encode(pub_obj.encrypt(msg))
        # 需要分段
        offset = 0
        res = []
        while length - offset > 0:
            if length - offset > max_length:
                res.append(pub_obj.encrypt(msg[offset:offset + max_length]))
            else:
                res.append(pub_obj.encrypt(msg[offset:]))
            offset += max_length
        byte_data = b''.join(res)

        return b64encode(byte_data)

    def long_decrypt_by_private_key(self, msg, private_key):
        """ 使用私钥分段解密 """
        msg = b64decode(msg)
        length = len(msg)
        private_key = RSA.importKey(b64decode(private_key))
        max_length = int(self.get_max_length(private_key, False))
        # 私钥解密
        private_obj = Cipher_pkcs1_v1_5.new(private_key)
        # 长度不用分段
        if length < max_length:
            return b''.join(private_obj.decrypt(msg, b'xyz'))
        # 需要分段
        offset = 0
        res = []
        while length - offset > 0:
            if length - offset > max_length:
                res.append(private_obj.decrypt(msg[offset:offset + max_length], b'xyz'))
            else:
                res.append(private_obj.decrypt(msg[offset:], b'xyz'))
            offset += max_length
        # RSA解密后再进行一次base64解密，也可以直接返回，这个看加密的数据有没有base64加密
        de_base_res = b64decode(b''.join(res))
        return de_base_res