RSA实现长文本的加密和解密

RSA算法一次能加密的名文长度与密钥长度成正比，如RSA 1024实际可加密的明文长度最大是1024bits。如果大于这个长度怎么办？分段加密：将需要加密的数据按照较小的片段进行切割，然后对每个片段单独进行加密操作。在接收方再将这些加密结果合并起来得到完整的加密结果。这样就能够绕开RSA算法的最大加密长度限制。

长文本RSA加密代码如下：

from Crypto import Random
from Crypto.PublicKey import RSA
from Crypto.Cipher import PKCS1_v1_5 as Cipher_pkcs1_v1_5
import base64


class Encryption(object):
    def __init__(self):
        # 伪随机数生成器
        self.random_generator = Random.new().read

    def getKey(self):
        # rsa算法生成实例
        rsa = RSA.generate(1024, self.random_generator)
        # master的秘钥对的生成
        private_pem = rsa.exportKey()
        public_pem = rsa.publickey().exportKey()
        key={}
        key["private"] = private_pem
        key["public"] = public_pem
        with open("./rsa.public.pem", mode="wb") as f:
            f.write(public_pem)

        with open("./rsa.private.pem", mode="wb") as f:
            f.write(private_pem)
        return key

    def rsa_long_encrypt(self, msg, pub_key_str,  length=100):
        """
        单次加密串的长度最大为 (key_size/8)-11
        1024bit的证书用100， 2048bit的证书用 200
        """
        pubobj = RSA.importKey(pub_key_str)
        pubobj = Cipher_pkcs1_v1_5.new(pubobj)
        res = []
        for i in range(0, len(msg), length):
            print(msg[i:i + length])
            res.append(
                str(
                    base64.b64encode(pubobj.encrypt(
                        msg[i:i + length].encode(encoding="utf-8"))), 'utf-8'
                )
            )
        for r in res:
            print(len(r))
        return "".join(res)

    def rsa_long_decrypt(self, msg, priv_key_str,  length=172):
        """
        1024bit的证书用128，2048bit证书用256位
        """
        privobj = RSA.importKey(priv_key_str)
        privobj = Cipher_pkcs1_v1_5.new(privobj)
        res = []
        for i in range(0, len(msg), length):
            res.append(
                str(
                    privobj.decrypt(
                        base64.b64decode(msg[i:i + length])
                        , 'xyz'), 'utf-8'
                )
            )
        print(res)
        return "".join(res)


if __name__ == '__main__':
    str1="""{"ans": [{"id": 5, "sno": "6", "name": "121", "brithday": "1234-01-02", "sex": "1", "tel": "2"}, {"id": 9, "sno": "99, "name": "121", "brithday": "1234-01-02", "sex": "1", "tel": "2"}"""*5
    a = Encryption()
    key = a.getKey()
    # with open("rsa.public.pem", mode="r") as f:
    #     pubkey = f.read()
    # cipher_text = a.rsa_long_encrypt(str1, pubkey)
    # print(cipher_text)
    # with open("rsa.private.pem", mode="r") as f:
    #     prikey = f.read()
    # plaintext = a.rsa_long_decrypt(cipher_text, prikey)
    # print(plaintext)