跳过 elif 声明？
Skipping elif statement?
我正在尝试使用 pycryptodome 创建一个简单的 encryption/decryption，但不断收到以下错误：
ValueError: Error 3 while encrypting in CBC mode
经过一番挖掘，我发现如果没有足够的数据进行加密，您会收到此错误，因为没有有效的填充。问题是我添加了一个填充函数。调试后，我的代码似乎完全跳过了填充部分并导致了这个错误。我做错了什么？
import os, random
from Crypto.Cipher import AES
from Crypto.Hash import SHA256
def encrypt(key, filename):
chunksize = 64*1024
outputfile = filename + "(encrypted)"
filesize = str(os.path.getsize(filename)).zfill(16)
IV =''
for i in range(16):
IV += chr(random.randint(0, 0xFF))
encryptor = AES.new(key, AES.MODE_CBC, IV.encode("latin-1"))
with open(filename, 'rb') as infile:
with open(outputfile, 'wb') as outfile:
outfile.write(filesize.encode("latin-1"))
outfile.write(IV.encode("latin-1"))
while True:
chunk = infile.read(chunksize)
print(len(chunk))
if len(chunk) == 0:
break
elif len(chunk) % 16 != 0:
chunk += ' ' * (16 - (len(chunk) % 16))
outfile.write(encryptor.encrypt(chunk))
def decrypt(key, filename):
chunksize = 64 *1024
outputfile = filename[:11]
with open(filename, 'rb') as infile:
filesize = int(infile.read(16))
IV = infile.read(16)
decryptor = AES.new(key, AES.MODE_CBC, IV.encode("latin-1"))
with open(outputfile, 'wb') as outfile:
while True:
chunk = infile.read(chunksize)
if len(chunk) == 0:
break
outfile.write(decryptor.decrypt(chunk))
outfile.truncate(filesize)
def getkey (password):
hasher = SHA256.new(password.encode("latin-1"))
return hasher.digest()
def main():
choice = input ("do you want to [E]ncrypt of [D]ecrypt?")
if choice == 'E':
filename = input("File to encrypt >")
password = input("Password >")
encrypt(getkey(password), filename)
print("Encryption done!")
elif choice == 'D':
filename = input("File to Decrypt >")
password = input("Password >")
decrypt(getkey(password), filename)
print("Decryption done!")
else:
print("No option selected")
if __name__ == '__main__':
main()
*我用的是python3.6
编辑：
这是我 运行 代码时的完整控制台输出：
C:\Users\itayg\AppData\Local\Programs\Python\Python36\python.exe "C:\Program Files\JetBrains\PyCharm Community Edition 2017.1.2\helpers\pydev\pydevd.py" --multiproc --qt-support --client 127.0.0.1 --port 21111 --file C:/Users/itayg/PycharmProjects/PyCrypto/encrypt.py
Connected to pydev debugger (build 171.4249.47)
pydev debugger: process 12876 is connecting
do you want to [E]ncrypt of [D]ecrypt?E
File to encrypt >grades.jpg
Password >123
65536
49373
Traceback (most recent call last):
File "C:\Program Files\JetBrains\PyCharm Community Edition 2017.1.2\helpers\pydev\pydevd.py", line 1585, in <module>
globals = debugger.run(setup['file'], None, None, is_module)
File "C:\Program Files\JetBrains\PyCharm Community Edition 2017.1.2\helpers\pydev\pydevd.py", line 1015, in run
pydev_imports.execfile(file, globals, locals) # execute the script
File "C:\Program Files\JetBrains\PyCharm Community Edition 2017.1.2\helpers\pydev\_pydev_imps\_pydev_execfile.py", line 18, in execfile
exec(compile(contents+"\n", file, 'exec'), glob, loc)
File "C:/Users/itayg/PycharmProjects/PyCrypto/encrypt.py", line 66, in <module>
main()
File "C:/Users/itayg/PycharmProjects/PyCrypto/encrypt.py", line 55, in main
encrypt(getkey(password), filename)
File "C:/Users/itayg/PycharmProjects/PyCrypto/encrypt.py", line 29, in encrypt
outfile.write(encryptor.encrypt(chunk))
File "C:\Users\itayg\AppData\Local\Programs\Python\Python36\lib\site-packages\pycryptodome-3.4.6-py3.6-win-amd64.egg\Crypto\Cipher\_mode_cbc.py", line 167, in encrypt
raise ValueError("Error %d while encrypting in CBC mode" % result)
ValueError: Error 3 while encrypting in CBC mode
好的，让我们修复您的代码中的一些错误。第一个最明显的 - 你的填充会在 Python 3.5+ 上中断（你的用户 'menu' 会在 2.x 上中断）因为 infile.read() 会给你 bytes数组，因此尝试添加由 chunk += ' ' * (16 - (len(chunk) % 16)) 形成的字符串会导致错误。您需要先将空白垫转换为 bytes 数组：chunk += b' ' * (16 - (len(chunk) % 16))
但是这样的空白填充不是个好主意 - 当您稍后解密文件时，您如何知道添加了多少填充（如果有）？您需要将其存储在某处 - 您通过 filesize 值在 'header' 中执行此操作，告诉潜在的攻击者您的文件到底有多大以及添加了多少填充，从而使您面临填充 oracle 攻击（这可以用下面的代码实现，所以不要在没有添加适当的 MAC 的情况下使用它来传递消息。
您可以使用许多强大的填充方案 - 我个人更喜欢 PKCS#7，它只是填充您的不均匀块或添加一个具有 n 字节数和值的全新块n - 这样，解密后，您可以从块中选择最后一个字节，并确切知道填充了多少字节，以便您可以剥离它们。因此，将您的加密部分替换为：
def encrypt(key, filename):
outputfile = filename + "(encrypted)"
chunksize = 1024 * AES.block_size # use the cipher's defined block size as a multiplier
IV = bytes([random.randint(0, 0xFF) for _ in range(AES.block_size)]) # bytes immediately
encryptor = AES.new(key, AES.MODE_CBC, IV)
with open(filename, 'rb') as infile:
with open(outputfile, 'wb') as outfile:
outfile.write(IV) # write the IV
padded = False
while not padded: # loop until the last block is padded
chunk = infile.read(chunksize)
chunk_len = len(chunk)
# if no more data or the data is shorter than the required block size
if chunk_len == 0 or chunk_len % AES.block_size != 0:
padding = AES.block_size - (chunk_len % AES.block_size)
chunk += bytes([padding]) * padding
# on Python 2.x replace with: chunk += chr(padding_len) * padding_len
padded = True
outfile.write(encryptor.encrypt(chunk))
我还更改了您的 chunksize 以匹配您使用的块大小（AES.block_size 的倍数）- 恰好 64 是 16 的倍数，但您应该注意那些东西。
现在我们已经解决了加密问题，解密就是所有这些，但是是相反的——解密所有块，读取最后一个块的最后一个字节，并从后面删除 n 个与值匹配的字节最后一个字节：
def decrypt(key, filename):
outputfile = filename[:-11] + "(decrypted)"
chunksize = 1024 * AES.block_size # use the cipher's defined block size as a multiplier
with open(filename, 'rb') as infile:
IV = infile.read(AES.block_size)
decryptor = AES.new(key, AES.MODE_CBC, IV)
with open(outputfile, 'wb') as outfile:
old_chunk = b'' # stores last chunk, needed for reading data with a delay
stripped = False
while not stripped: # delayed loop until the last block is stripped
chunk = decryptor.decrypt(infile.read(chunksize)) # decrypt as we read
if len(chunk) == 0: # no more data
padding = old_chunk[-1] # pick the padding value from the last byte
if old_chunk[-padding:] != bytes([padding]) * padding:
raise ValueError("Invalid padding...")
old_chunk = old_chunk[:-padding] # strip the padding
stripped = True
outfile.write(old_chunk) # write down the 'last' chunk
old_chunk = chunk # set the new chunk for checking in the next loop
我正在尝试使用 pycryptodome 创建一个简单的 encryption/decryption，但不断收到以下错误：
ValueError: Error 3 while encrypting in CBC mode
经过一番挖掘，我发现如果没有足够的数据进行加密，您会收到此错误，因为没有有效的填充。问题是我添加了一个填充函数。调试后，我的代码似乎完全跳过了填充部分并导致了这个错误。我做错了什么？
import os, random
from Crypto.Cipher import AES
from Crypto.Hash import SHA256
def encrypt(key, filename):
chunksize = 64*1024
outputfile = filename + "(encrypted)"
filesize = str(os.path.getsize(filename)).zfill(16)
IV =''
for i in range(16):
IV += chr(random.randint(0, 0xFF))
encryptor = AES.new(key, AES.MODE_CBC, IV.encode("latin-1"))
with open(filename, 'rb') as infile:
with open(outputfile, 'wb') as outfile:
outfile.write(filesize.encode("latin-1"))
outfile.write(IV.encode("latin-1"))
while True:
chunk = infile.read(chunksize)
print(len(chunk))
if len(chunk) == 0:
break
elif len(chunk) % 16 != 0:
chunk += ' ' * (16 - (len(chunk) % 16))
outfile.write(encryptor.encrypt(chunk))
def decrypt(key, filename):
chunksize = 64 *1024
outputfile = filename[:11]
with open(filename, 'rb') as infile:
filesize = int(infile.read(16))
IV = infile.read(16)
decryptor = AES.new(key, AES.MODE_CBC, IV.encode("latin-1"))
with open(outputfile, 'wb') as outfile:
while True:
chunk = infile.read(chunksize)
if len(chunk) == 0:
break
outfile.write(decryptor.decrypt(chunk))
outfile.truncate(filesize)
def getkey (password):
hasher = SHA256.new(password.encode("latin-1"))
return hasher.digest()
def main():
choice = input ("do you want to [E]ncrypt of [D]ecrypt?")
if choice == 'E':
filename = input("File to encrypt >")
password = input("Password >")
encrypt(getkey(password), filename)
print("Encryption done!")
elif choice == 'D':
filename = input("File to Decrypt >")
password = input("Password >")
decrypt(getkey(password), filename)
print("Decryption done!")
else:
print("No option selected")
if __name__ == '__main__':
main()
*我用的是python3.6
编辑： 这是我 运行 代码时的完整控制台输出：
C:\Users\itayg\AppData\Local\Programs\Python\Python36\python.exe "C:\Program Files\JetBrains\PyCharm Community Edition 2017.1.2\helpers\pydev\pydevd.py" --multiproc --qt-support --client 127.0.0.1 --port 21111 --file C:/Users/itayg/PycharmProjects/PyCrypto/encrypt.py
Connected to pydev debugger (build 171.4249.47)
pydev debugger: process 12876 is connecting
do you want to [E]ncrypt of [D]ecrypt?E
File to encrypt >grades.jpg
Password >123
65536
49373
Traceback (most recent call last):
File "C:\Program Files\JetBrains\PyCharm Community Edition 2017.1.2\helpers\pydev\pydevd.py", line 1585, in <module>
globals = debugger.run(setup['file'], None, None, is_module)
File "C:\Program Files\JetBrains\PyCharm Community Edition 2017.1.2\helpers\pydev\pydevd.py", line 1015, in run
pydev_imports.execfile(file, globals, locals) # execute the script
File "C:\Program Files\JetBrains\PyCharm Community Edition 2017.1.2\helpers\pydev\_pydev_imps\_pydev_execfile.py", line 18, in execfile
exec(compile(contents+"\n", file, 'exec'), glob, loc)
File "C:/Users/itayg/PycharmProjects/PyCrypto/encrypt.py", line 66, in <module>
main()
File "C:/Users/itayg/PycharmProjects/PyCrypto/encrypt.py", line 55, in main
encrypt(getkey(password), filename)
File "C:/Users/itayg/PycharmProjects/PyCrypto/encrypt.py", line 29, in encrypt
outfile.write(encryptor.encrypt(chunk))
File "C:\Users\itayg\AppData\Local\Programs\Python\Python36\lib\site-packages\pycryptodome-3.4.6-py3.6-win-amd64.egg\Crypto\Cipher\_mode_cbc.py", line 167, in encrypt
raise ValueError("Error %d while encrypting in CBC mode" % result)
ValueError: Error 3 while encrypting in CBC mode
好的，让我们修复您的代码中的一些错误。第一个最明显的 - 你的填充会在 Python 3.5+ 上中断（你的用户 'menu' 会在 2.x 上中断）因为 infile.read() 会给你 bytes数组，因此尝试添加由 chunk += ' ' * (16 - (len(chunk) % 16)) 形成的字符串会导致错误。您需要先将空白垫转换为 bytes 数组：chunk += b' ' * (16 - (len(chunk) % 16))
但是这样的空白填充不是个好主意 - 当您稍后解密文件时，您如何知道添加了多少填充（如果有）？您需要将其存储在某处 - 您通过 filesize 值在 'header' 中执行此操作，告诉潜在的攻击者您的文件到底有多大以及添加了多少填充，从而使您面临填充 oracle 攻击（这可以用下面的代码实现，所以不要在没有添加适当的 MAC 的情况下使用它来传递消息。
您可以使用许多强大的填充方案 - 我个人更喜欢 PKCS#7，它只是填充您的不均匀块或添加一个具有 n 字节数和值的全新块n - 这样，解密后，您可以从块中选择最后一个字节，并确切知道填充了多少字节，以便您可以剥离它们。因此，将您的加密部分替换为：
def encrypt(key, filename):
outputfile = filename + "(encrypted)"
chunksize = 1024 * AES.block_size # use the cipher's defined block size as a multiplier
IV = bytes([random.randint(0, 0xFF) for _ in range(AES.block_size)]) # bytes immediately
encryptor = AES.new(key, AES.MODE_CBC, IV)
with open(filename, 'rb') as infile:
with open(outputfile, 'wb') as outfile:
outfile.write(IV) # write the IV
padded = False
while not padded: # loop until the last block is padded
chunk = infile.read(chunksize)
chunk_len = len(chunk)
# if no more data or the data is shorter than the required block size
if chunk_len == 0 or chunk_len % AES.block_size != 0:
padding = AES.block_size - (chunk_len % AES.block_size)
chunk += bytes([padding]) * padding
# on Python 2.x replace with: chunk += chr(padding_len) * padding_len
padded = True
outfile.write(encryptor.encrypt(chunk))
我还更改了您的 chunksize 以匹配您使用的块大小（AES.block_size 的倍数）- 恰好 64 是 16 的倍数，但您应该注意那些东西。
现在我们已经解决了加密问题，解密就是所有这些，但是是相反的——解密所有块，读取最后一个块的最后一个字节，并从后面删除 n 个与值匹配的字节最后一个字节：
def decrypt(key, filename):
outputfile = filename[:-11] + "(decrypted)"
chunksize = 1024 * AES.block_size # use the cipher's defined block size as a multiplier
with open(filename, 'rb') as infile:
IV = infile.read(AES.block_size)
decryptor = AES.new(key, AES.MODE_CBC, IV)
with open(outputfile, 'wb') as outfile:
old_chunk = b'' # stores last chunk, needed for reading data with a delay
stripped = False
while not stripped: # delayed loop until the last block is stripped
chunk = decryptor.decrypt(infile.read(chunksize)) # decrypt as we read
if len(chunk) == 0: # no more data
padding = old_chunk[-1] # pick the padding value from the last byte
if old_chunk[-padding:] != bytes([padding]) * padding:
raise ValueError("Invalid padding...")
old_chunk = old_chunk[:-padding] # strip the padding
stripped = True
outfile.write(old_chunk) # write down the 'last' chunk
old_chunk = chunk # set the new chunk for checking in the next loop