Decrypts entries in chunks of 32 bytes with the XOR key for JoJo ASB/EoH sound *_ev.xfbin files.

ev_decrypt.py

#!/usr/bin/env python

__author__ = 'SutandoTsukai181'
__license__ = "MIT"
__version__ = '1.0'

import os
from itertools import cycle
from sys import argv

KEY = b'\x8C\x91\x9B\x9A\x89\xD1\x87\x99\x9D\x96\x91'

ENTRY_LEN = 32
BLOCK_LEN = 4

HELP = f"""{argv[0]} v{__version__}
By {__author__}

Decrypts entries in chunks of {ENTRY_LEN} bytes with the XOR key for JoJo ASB/EoH sound '_ev.xfbin' files.

Usage: {argv[0]} IN_PATH OUT_PATH

IN_PATH: path to input file with encrypted bytes
IN_PATH: path to output decrypted file
"""


def decrypt(path: str, out_path: str = None):
    result = bytearray()

    if not out_path:
        out_path = path + ('.decrypted')

    if not os.path.isfile(path):
        raise Exception(f'File does not exist: {path}')

    print('Decrypting...')

    with open(path, 'rb') as f:
        file = bytearray(f.read())

        # align to entry size
        if len(file) % ENTRY_LEN:
            file.extend([0] * (ENTRY_LEN - (len(file) % ENTRY_LEN)))

    for i in range(len(file) // ENTRY_LEN):
        entry = file[i*ENTRY_LEN: (i+1)*ENTRY_LEN]

        cur_key = cycle(KEY)
        for j in range(ENTRY_LEN // BLOCK_LEN):
            block = entry[j*BLOCK_LEN: (j+1)*BLOCK_LEN]
            result.extend(list(map(lambda x: x ^ next(cur_key), block))[::-1])

    with open(out_path, 'wb') as f:
        f.write(result)

    print(f'Result was written to {out_path}')


def main():
    if len(argv) == 2:
        decrypt(argv[1])
    elif len(argv) == 3:
        decrypt(argv[1], argv[2])
    else:
        print(HELP)
        os.system('pause')


if __name__ == '__main__':
    main()

Link to encryption script: encrypt_ev.py

Encryption and decryption are 2 separate scripts (despite the code mostly being the same) for the convenience of being able to drag and drop files into each script.