Feature: Add support for encrypted archives

[fdellwing]

Is your feature request related to a problem? Please describe.
n/a

Describe the solution you'd like
Fully support compressing and decompressing with password.

Describe alternatives you've considered
n/a

Additional context
n/a

[miurahr]

Now trial to implement decryption on topic branch https://github.com/miurahr/py7zr/tree/topic-decrypt-aes
Here is a big problem about AES encryption/decryption library on python.

The branch uses pycrypto but it was released in 2013 and no update now. That is because, installation is failed on Windows 10/MSVC 2015/Pytohn 3.6.

@fdellwing do you know any library which support AES and SHA256 on modern python and OSes?

[miurahr]

https://nitratine.net/blog/post/python-encryption-and-decryption-with-pycryptodome/ may be an option.

[andormarkus]

@miurahr

I have tested the module for large .csv file and it can not decompress it. I got the following error

ValueError: Data must be padded to 16 byte boundary in CBC mode

How to reproduce the error:

1. Get some large (few gb) csv file and compress it to 7z.
   My sampe file: http://sdm.lbl.gov/fastbit/data/star2002-full.csv.gz
   I have decompressed and recompressed with the following code:
   7z a large_w_pwd.7z star2002-full.csv -p1234

2. Try to uncompress with py7zr
   import py7zr
archive = py7zr.SevenZipFile('large_w_pwd.7z', mode='r', password='1234')
print(archive.getnames())
archive.extractall()

Full error log:

Traceback (most recent call last):
File "unzip.py", line 19, in
archive.extractall()
File "/home/amarkus/.pyenv/versions/3.7.3/lib/python3.7/site-packages/py7zr/py7zr.py", line 766, in extractall
self.worker.extract(self.fp, multithread=multi_thread)
File "/home/amarkus/.pyenv/versions/3.7.3/lib/python3.7/site-packages/py7zr/compression.py", line 288, in extract
self.extract_single(fp, self.files, self.src_start)
File "/home/amarkus/.pyenv/versions/3.7.3/lib/python3.7/site-packages/py7zr/compression.py", line 300, in extract_single
self.decompress(fp, f.folder, fileish, f.uncompressed[-1], f.compressed)
File "/home/amarkus/.pyenv/versions/3.7.3/lib/python3.7/site-packages/py7zr/compression.py", line 316, in decompress
tmp = decompressor.decompress(inp, max_length)
File "/home/amarkus/.pyenv/versions/3.7.3/lib/python3.7/site-packages/py7zr/compression.py", line 450, in decompress
folder_data = self.decompressor.decompress(data, max_length=max_length)
File "/home/amarkus/.pyenv/versions/3.7.3/lib/python3.7/site-packages/py7zr/compression.py", line 247, in decompress
temp = self.cipher.decrypt(data)
File "/home/amarkus/.pyenv/versions/3.7.3/lib/python3.7/site-packages/Crypto/Cipher/_mode_cbc.py", line 246, in decrypt
raise ValueError("Data must be padded to %d byte boundary in CBC mode" % self.block_size)
ValueError: Data must be padded to 16 byte boundary in CBC mode

[miurahr]

AES CBC mode is a block cipher which use 16byte block.
Current implementation does not handle this. https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation

[andormarkus]

Please can you modify decompress method in the AESDecompressor class so I can decompress large file with this package? It would be life changing for me.

I tried to pad the data before decryption and unpad after it. Did not work.
def decompress(self, data: bytes, max_length: Optional[int] = None) -> bytes:
padded_data = pad(data, AES.block_size)
decrypted_data = self.cipher.decrypt(padded_data)
unpadded_data = unpad(decrypted_data, AES.block_size)
temp = unpadded_data
return self.lzma_decompressor.decompress(temp, max_length)

File "/home/amarkus/.pyenv/versions/3.7.3/lib/python3.7/site-packages/py7zr/compression.py", line 249, in decompress
unpadded_data = unpad(decrypted_data, AES.block_size)
File "/home/amarkus/.pyenv/versions/3.7.3/lib/python3.7/site-packages/Crypto/Util/Padding.py", line 90, in unpad
raise ValueError("Padding is incorrect.")
ValueError: Padding is incorrect.

[miurahr]

Could you provide me a test data with minimal size(-kb) to reproduce the issue?