Unable to compress large files

[Finnimbrun]

My file is larger than 900M and it doesn't seem to work.

[devthat]

I tried this out and it eventually works with a 1gb file. The problem however is, that it takes a really long time compared to compressing without a password. I have to investigate this further.

[auto-Dog]

Seems that compressor and decompressor computes slow if you only use python variable and code to compute. Similar prolem exist in python module ZipFile, where ZipCrypto algorithm are implentment in python.

https://github.com/devthat/zipencrypt/blob/897f03d05f5b2881e915ed346d0498f58abf3ac8/zipencrypt/zipencrypt3.py#L573C7-L573C20

I think it might work if cython or C Python API is used to accelerate compute. For example, replace the functions above, using cython. After compile the pyx file, directly use it as a module.

** But the speed just doubled with this code, so I also wonder if there's better way to accelerate **

# in weak_decrypt .pyx
cdef class weak_decrypt:
    cdef public unsigned long key_0
    cdef public unsigned long key_1
    cdef public unsigned long key_2

    def __cinit__(self):
        self.key_0 = 305419896
        self.key_1 = 591751049
        self.key_2 = 878082192

    def update_keys(self,int byte):
        crc32 = zlib.crc32
        bytes_c = bytes
        cdef unsigned long factor = 134775813
        self.key_0 = ~crc32(bytes_c((byte,)), ~self.key_0) & 0xFFFFFFFF
        self.key_1 = (self.key_1 + (self.key_0 & 0xFF)) & 0xFFFFFFFF
        self.key_1 = ((self.key_1 * factor) + 1) & 0xFFFFFFFF
        # self.key_1 = ((self.key_1 * 0x8088405) + 1) & 0xFFFFFFFF
        self.key_2 = ~crc32(bytes_c((self.key_1 >> 24,)), ~self.key_2) & 0xFFFFFFFF
    def decrypt(self,chunk):
        chunk = bytearray(chunk)
        cdef int byte
        cdef int i
        cdef int temp
        for i, byte in enumerate(chunk):
            temp = self.key_2 | 2
            byte ^= ((temp * (temp ^ 1)) >> 8) & 0xFF
            self.update_keys(byte)
            chunk[i] = byte
        return bytes(chunk)

# usage in other py file:
# from weak_decrypt import weak_decrypt
# dec = weak_decrypt()
# out = dec.decrypt(input_byte)

[devthat]

Nice solution! However, this makes packaging more complicated since you would need to package binaries or do the cython compilation during installation - if that's possible.