feat: AES-2 encryption #94
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Without this for some reason the following error can happen if when we add other dependencies in later commits: > ImportError: cannot import name 'Config' from 'pytest' (Specifically the dependencies of pycryptodome and pyzipper) Have to admit I'm not really sure why, and haven't spent that long trying to work out why, but I think it's reasonable to use a more recent version even without this issue and not really worth the time investigating it. We're not using the most recent version of pytest because I don't think it can be installed with Python 3.6.7 that we're still testing on. Will like to maintain support for older Python for as long as possible to not cause annoyances for people that are restricted to older Python but want the latest stream-zip.
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This reduces a little big of duplication for each mode - the flags are now defined in a single line. Also, the flags are defined as a 2-byte unsigned integer rather than a 2-byte bytes array. This changes allow for the flags to be more easily dynamic for each mode - set in a single place and then use binary or | to combine flags. This will be useful in the upcoming chnage that adds AES encryption for each mode that will require the first bit of the flags to be set if encryption is enabled.
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This reduces a bit of duplication, and more easily allows the compression type of "99" to be set in a later commit, which is one of the things that indicates that AES encryption is used.
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This adds AES-2 encryption as requested/discussed in #93 and defined at https://www.winzip.com/en/support/aes-encryption/ For now, AES-2 is used over AES-1 to prevent leakage of information via CRC-32 for small files, at the price of not having a checksum on the uncompressed plain text data (although there is an HMAC check on the encrypted compressed data as part of AES-2). In a later change, we should be able to make it AES-1 for larger files as recommended at https://www.winzip.com/en/support/aes-encryption/, but not doing this now to keep this change reasonably small.
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This adds AES-2 encryption as requested/discussed in #93 and defined at https://www.winzip.com/en/support/aes-encryption/
For now, AES-2 is used over AES-1 to prevent leakage of information via CRC-32 for small files, at the price of not having a checksum on the uncompressed plain text data (although there is an HMAC check on the encrypted compressed data as part of AES-2). In a later change, we should be able to make it AES-1 for larger files as recommended at https://www.winzip.com/en/support/aes-encryption/, but not doing this now to keep this change reasonably small.