1、PyCryptodome的padding方法

pad和unpad函数是从Crypto.Util复制的。填充并修改为只使用PKCS7填充。注意，当使用PKCS7填充时，填充最后一个块是很重要的，即使它的大小是块大小的倍数，否则您将无法正确地解填充。

try:
    from Crypto.Util.Padding import pad, unpad
except ImportError:
    from Crypto.Util.py3compat import bchr, bord
    def pad(data_to_pad, block_size):
        padding_len = block_size-len(data_to_pad)%block_size
        padding = bchr(padding_len)*padding_len
        return data_to_pad + padding
    def unpad(padded_data, block_size):
        pdata_len = len(padded_data)
        if pdata_len % block_size:
            raise ValueError("Input data is not padded")
        padding_len = bord(padded_data[-1])
        if padding_len<1 or padding_len>min(block_size, pdata_len):
            raise ValueError("Padding is incorrect.")
        if padded_data[-padding_len:]!=bchr(padding_len)*padding_len:
            raise ValueError("PKCS#7 padding is incorrect.")
        return padded_data[:-padding_len]

2、文件加密和解密方法

1）加密方法代码

def encrypt_file(key, in_filename, out_filename=None, chunksize=64*1024):
    if not out_filename:
        out_filename = in_filename + '.enc'
    iv = os.urandom(16)
    encryptor = AES.new(key, AES.MODE_CBC, iv)
    filesize = os.path.getsize(in_filename)
    with open(in_filename, 'rb') as infile:
        with open(out_filename, 'wb') as outfile:
            outfile.write(struct.pack('<Q', filesize))
            outfile.write(iv)
            pos = 0
            while pos < filesize:
                chunk = infile.read(chunksize)
                pos += len(chunk)
                if pos == filesize:
                    chunk = pad(chunk, AES.block_size)
                outfile.write(encryptor.encrypt(chunk))

2）解密方法代码

def decrypt_file(key, in_filename, out_filename=None, chunksize=64*1024):
    if not out_filename:
        out_filename = in_filename + '.dec'
    with open(in_filename, 'rb') as infile:
        filesize = struct.unpack('<Q', infile.read(8))[0]
        iv = infile.read(16)
        encryptor = AES.new(key, AES.MODE_CBC, iv)
        with open(out_filename, 'wb') as outfile:
            encrypted_filesize = os.path.getsize(in_filename)
            pos = 8 + 16 # the filesize and IV.
            while pos < encrypted_filesize:
                chunk = infile.read(chunksize)
                pos += len(chunk)
                chunk = encryptor.decrypt(chunk)
                if pos == encrypted_filesize:
                    chunk = unpad(chunk, AES.block_size)
                outfile.write(chunk)

注意：上面代码与Python2/Python3兼容，它应该可以与PyCryptodome或PyCrypto一起使用。

但是，虽然本文介绍的是PyCrypto，还是建议您更新到PyCryptodome。PyCryptodome是PyCrypto的一个分支，它公开了相同的API(因此您不需要过多地更改代码)，还提供了一些额外的特性:填充函数、经过身份验证的加密算法、KDFs等。另一方面，PyCrypto不再被维护，而且一些版本还存在基于堆的缓冲区溢出漏洞。

安装PyCryptodome使用下面命令：

pip install PyCryptodome

3、完整代码

import os, random, struct
from Crypto.Cipher import AES
try:
    from Crypto.Util.Padding import pad, unpad
except ImportError:
    from Crypto.Util.py3compat import bchr, bord
    def pad(data_to_pad, block_size):
        padding_len = block_size-len(data_to_pad)%block_size
        padding = bchr(padding_len)*padding_len
        return data_to_pad + padding
    def unpad(padded_data, block_size):
        pdata_len = len(padded_data)
        if pdata_len % block_size:
            raise ValueError("Input data is not padded")
        padding_len = bord(padded_data[-1])
        if padding_len<1 or padding_len>min(block_size, pdata_len):
            raise ValueError("Padding is incorrect.")
        if padded_data[-padding_len:]!=bchr(padding_len)*padding_len:
            raise ValueError("PKCS#7 padding is incorrect.")
        return padded_data[:-padding_len]
def encrypt_file(key, in_filename, out_filename=None, chunksize=64*1024):
    if not out_filename:
        out_filename = in_filename + '.enc'
    iv = os.urandom(16)
    encryptor = AES.new(key, AES.MODE_CBC, iv)
    filesize = os.path.getsize(in_filename)
    with open(in_filename, 'rb') as infile:
        with open(out_filename, 'wb') as outfile:
            outfile.write(struct.pack('<Q', filesize))
            outfile.write(iv)
            pos = 0
            while pos < filesize:
                chunk = infile.read(chunksize)
                pos += len(chunk)
                if pos == filesize:
                    chunk = pad(chunk, AES.block_size)
                outfile.write(encryptor.encrypt(chunk))
def decrypt_file(key, in_filename, out_filename=None, chunksize=64*1024):
    if not out_filename:
        out_filename = in_filename + '.dec'
    with open(in_filename, 'rb') as infile:
        filesize = struct.unpack('<Q', infile.read(8))[0]
        iv = infile.read(16)
        encryptor = AES.new(key, AES.MODE_CBC, iv)
        with open(out_filename, 'wb') as outfile:
            encrypted_filesize = os.path.getsize(in_filename)
            pos = 8 + 16 # the filesize and IV.
            while pos < encrypted_filesize:
                chunk = infile.read(chunksize)
                pos += len(chunk)
                chunk = encryptor.decrypt(chunk)
                if pos == encrypted_filesize:
                    chunk = unpad(chunk, AES.block_size)
                outfile.write(chunk) 
#测试代码
if __name__=='__main__':
    encrypt_file("keyskeyskeyskeys".encode('utf-8'),"/root/myfile")
    decrypt_file("keyskeyskeyskeys".encode('utf-8'),"/root/myfile.enc")