Python黑客编程之数据加解密

描述

• 利用非对称密钥RSA和对称密钥AES算法对传输数据进行加密

分析

• 发送方本地保存有RSA公钥，发送数据前，利用AES算法对传输数据明文进行加密，利用RSA算法对AES的密钥进行加密
• 将密钥的密文和数据的密文打包到一块进行传输
• 接收方本地保存有RSA密钥，接收数据后，对传输密文进行拆分，利用RSA算法对AES密钥进行解密，然后利用AES算法还原数据明文

相关知识

• 常用编码方法对比
  • arscii: 可见字符与不可见字符，同二进制字节的映射关系
  • unicode: 增加了对中文等语言的支持
  • utf-8: unicode的最常用的实现方式，变长编码，使用1~4个字节表示一个符号，对于单字节的符号，字节的第一位设为0，后面7位为这个符号的 Unicode 码。因此对于英语字母，UTF-8编码和ASCII码是相同的
    • python的encoding函数默认编码是utf-8，常用于转换python的字符串对象和字节流对象
  • gbk: 国标，中文编码是双字节来表示的，英文编码是用ascii来表示，即单字节
  • base64: 用64个可打印字符来表示二进制数据
    • 一般用于在HTTP协议下传输数据，因为HTTP协议是文本传输协议，需要将二进制数据转化为字符数据，但直接转换是不行的，因为网络只能传输可打印字符，base64应运而生
    • 编码与解码的处理对象是byte，故对原数据要先编码，使原本的str类型变成byte，解码后直接输出来的是byte对象，故要解码成str对象

代码

• 生成RSA公钥和密钥

def generate():
    new_key = RSA.generate(2048)
    private_key = new_key.exportKey()
    public_key = new_key.public_key().exportKey()

    with open('key.pri', 'wb') as f:
        f.write(private_key)

    with open('key.pub', 'wb') as f:
        f.write(public_key)

• 加密：利用AES加密数据，同时用RSA对AES密钥进行加密，将加密后的部分合并，base64编码后传输

def encrypt(plaintext):
    compressed_text = zlib.compress(plaintext)
    session_key = get_random_bytes(16)

    cipher_aes = AES.new(session_key, AES.MODE_EAX)
    ciphertext, tag = cipher_aes.encrypt_and_digest(compressed_text)
    cipher_rsa, _ = get_rsa_cipher('pub')

    encrypted_session_key = cipher_rsa.encrypt(session_key)
    msg_payload = encrypted_session_key + cipher_aes.nonce + tag + ciphertext
    encrypted = base64.encodebytes(msg_payload)
    return encrypted

• 解密：base64解码密文，用bytesIO对象拆分出密钥和数据部分，读取本地的RSA密钥，用RSA解密出AES的密钥，再用AES解密出明文数据

def decrypt(encrypted):
    encrypted_bytes = BytesIO(base64.decodebytes(encrypted))
    cipher_rsa, keysize_in_bytes = get_rsa_cipher('pri')

    encrypted_session_key = encrypted_bytes.read(keysize_in_bytes)
    nonce = encrypted_bytes.read(16)
    tag = encrypted_bytes.read(16)
    ciphertext = encrypted_bytes.read()

    session_key = cipher_rsa.decrypt(encrypted_session_key)
    cipher_aes = AES.new(session_key, AES.MODE_EAX, nonce)
    decrypted = cipher_aes.decrypt_and_verify(ciphertext, tag)

    plaintext = zlib.decompress(decrypted)
    return plaintext

def get_rsa_cipher(keytype):
    with open(f'key.{keytype}') as f:
        key = f.read()
    rsakey = RSA.importKey(key)
    return (PKCS1_OAEP.new(rsakey), rsakey.size_in_bytes())

• 完整代码

from Cryptodome.Cipher import AES, PKCS1_OAEP
from Cryptodome.PublicKey import RSA
from Cryptodome.Random import get_random_bytes
from io import BytesIO

import base64
import zlib

def generate():
    new_key = RSA.generate(2048)
    private_key = new_key.exportKey()
    public_key = new_key.public_key().exportKey()

    with open('key.pri', 'wb') as f:
        f.write(private_key)

    with open('key.pub', 'wb') as f:
        f.write(public_key)

def get_rsa_cipher(keytype):
    with open(f'key.{keytype}') as f:
        key = f.read()
    rsakey = RSA.importKey(key)
    return (PKCS1_OAEP.new(rsakey), rsakey.size_in_bytes())

def encrypt(plaintext):
    compressed_text = zlib.compress(plaintext)
    session_key = get_random_bytes(16)

    cipher_aes = AES.new(session_key, AES.MODE_EAX)
    ciphertext, tag = cipher_aes.encrypt_and_digest(compressed_text)
    cipher_rsa, _ = get_rsa_cipher('pub')

    encrypted_session_key = cipher_rsa.encrypt(session_key)
    msg_payload = encrypted_session_key + cipher_aes.nonce + tag + ciphertext
    encrypted = base64.encodebytes(msg_payload)
    return encrypted

def decrypt(encrypted):
    encrypted_bytes = BytesIO(base64.decodebytes(encrypted))
    cipher_rsa, keysize_in_bytes = get_rsa_cipher('pri')

    encrypted_session_key = encrypted_bytes.read(keysize_in_bytes)
    nonce = encrypted_bytes.read(16)
    tag = encrypted_bytes.read(16)
    ciphertext = encrypted_bytes.read()

    session_key = cipher_rsa.decrypt(encrypted_session_key)
    cipher_aes = AES.new(session_key, AES.MODE_EAX, nonce)
    decrypted = cipher_aes.decrypt_and_verify(ciphertext, tag)

    plaintext = zlib.decompress(decrypted)
    return plaintext

if __name__ == "__main__":
    generate()
    plaintext = b"This is a secrete message, right?"
    print(decrypt(encrypt(plaintext)))

测试结果

• 通过加密解密，还原出原文数据