长度不正确的pycrypto密文

Question

我用pycrypto生成了一个公钥和私钥，并使用导出密钥将它们保存到一个文件中：

from Crypto.PublicKey import RSA
bits=2048
new_key = RSA.generate(bits, e=65537)

prv = open('keymac.pem','w')
prv.write(new_key.exportKey('PEM'))
prv.close()
pub = open('pubmac.pem', 'w')
pub.write(new_key.publickey().exportKey('PEM'))
pub.close()

我使用公钥加密文件（在http://insiderattack.blogspot.com/2014/07/encrypted-file-transfer-utility-in.html#comment-form之后）

当我读取文件解密时，我得到“长度不正确的密文”

我在Deepal Jayasekara的解密代码周围添加了一个try-except块示例：

try:
    encryptedonetimekey = filetodecrypt.read(512)
    privatekey = open("keymac.pem", 'r').read()
    rsaofprivatekey = RSA.importKey(privatekey)
    pkcs1ofprivatekey = PKCS1_OAEP.new(rsaofprivatekey)
    aesonetimekey = pkcs1ofprivatekey.decrypt(encryptedonetimekey)

   except Exception as decrypprivkeyerr:
       print "Decryption of the one time key using the private key        failed!!"
       print "Key error == %s" %decrypprivkeyerr
     raise Exception("Decryption using Private key failed error = %s" %decrypprivkeyerr)

我遗漏了什么吗？我应该以不同的方式保存私钥吗？我没有正确阅读私钥吗？

Answer 1

错误信息“长度不正确的密文”告诉了我们所有人。也就是说， 密码文本超出了可以计算的限制长度（密钥长度， 1024.2048..）/8。为了解决这个问题，您可以分离密码文本并解密 它们在一个循环中，然后集合所有解密的字节字符串。我在Python 3.6中的代码供参考：

# 1024/8
default_length = 128
encrypt_str = str(data["content"])
sign_str = str(data["sign"])
try:
    rsa_private_key = RSA.importKey(private_key)
    encrypt_byte = base64.b64decode(encrypt_str.encode())
    length = len(encrypt_byte)
    cipher = PKCS115_Cipher(rsa_private_key)
    if length < default_length:
        decrypt_byte = cipher.decrypt(encrypt_byte, 'failure')
    else:
        offset = 0
        res = []
        while length - offset > 0:
            if length - offset > default_length:
                res.append(cipher.decrypt(encrypt_byte[offset: offset + 
                    default_length], 'failure'))
            else:
                res.append(cipher.decrypt(encrypt_byte[offset:], 'failure'))
            offset += default_length
        decrypt_byte = b''.join(res)
    decrypted = decrypt_byte.decode()

Answer 2

这并不能直接回答你的问题，但可能会给你一些问题的线索。Im使用两个函数将内容加密到文件，而不是直接加密文件。一个用于对文件进行加密（在我的例子中是用户名和密码），另一个用于根据需要对数据进行解密。

注意填充物的需要

在文件中创建加密内容：

from Crypto.Cipher import AES
import base64
import os
import argparse

parser = argparse.ArgumentParser(description='Arguments used to generate new credentials file, Use: -u for username, -p for password')
parser.add_argument('-u', help='Specify username', required=True)
parser.add_argument('-p', help='Specify password', required=True)
parser.add_argument('-b', help='Specify debug', required=False, action='store_true')
args = vars(parser.parse_args())


def encrypt(username, password):
    #Encrypt Credentials To '.creds' file, including 'secret' for username and password
    dir_path = os.path.dirname(os.path.realpath(__file__))
    # the block size for the cipher object; must be 16 per FIPS-197
    BLOCK_SIZE = 16

    # the character used for padding--with a block cipher such as AES, the value
    # you encrypt must be a multiple of BLOCK_SIZE in length.  This character is
    # used to ensure that your value is always a multiple of BLOCK_SIZE
    PADDING = '{'

    # one-liner to sufficiently pad the text to be encrypted
    pad = lambda s: s + (BLOCK_SIZE - len(s) % BLOCK_SIZE) * PADDING

    # generate a random secret key
    user_secret = os.urandom(BLOCK_SIZE)
    pass_secret = os.urandom(BLOCK_SIZE)

    # one-liners to encrypt/encode and decrypt/decode a string
    # encrypt with AES, encode with base64

    EncodeAES = lambda c, s: base64.b64encode(c.encrypt(pad(s)))
    # create a cipher object using the random secret
    user_cipher = AES.new(user_secret)
    pass_cipher = AES.new(pass_secret)

    # encode a string
    user_encoded = EncodeAES(user_cipher, username)
    pass_encoded = EncodeAES(pass_cipher, password)
    try:
        with open('.creds', 'w') as filename:
            filename.write(user_encoded + '\n')
            filename.write(user_secret + '\n')
            filename.write(pass_encoded + '\n')
            filename.write(pass_secret + '\n')
            filename.close()
            print '\nFile Written To: ', dir_path + '/.creds'
    except Exception, e:
        print e

    if args['b']:
        print((user_encoded, user_secret), (pass_encoded, pass_secret))

username = args['u']
password = args['p']

encrypt(username, password)

解密数据

def decrypt(dir_path, filename):
    #Read '.creds' file and return unencrypted credentials (user_decoded, pass_decoded)

    lines = [line.rstrip('\n') for line in open(dir_path + filename)]

    user_encoded = lines[0]
    user_secret = lines[1]
    pass_encoded = lines[2]
    pass_secret = lines[3]

    # the character used for padding--with a block cipher such as AES, the value
    # you encrypt must be a multiple of BLOCK_SIZE in length.  This character is
    # used to ensure that your value is always a multiple of BLOCK_SIZE
    PADDING = '{'

    DecodeAES = lambda c, e: c.decrypt(base64.b64decode(e)).rstrip(PADDING)

    # create a cipher object using the random secret
    user_cipher = AES.new(user_secret)
    pass_cipher = AES.new(pass_secret)

    # decode the encoded string
    user_decoded = DecodeAES(user_cipher, user_encoded)
    pass_decoded = DecodeAES(pass_cipher, pass_encoded)

    return (user_decoded, pass_decoded)