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45 lines
992 B
Python
45 lines
992 B
Python
import os
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import sys
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def key_schedule(key):
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keylength = len(key)
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S = range(256)
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j = 0
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for i in range(256):
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k = ord(key[i % keylength])
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j = (j + S[i] + k) % 256
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S[i], S[j] = S[j], S[i] # swap
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return S, j
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with open(sys.argv[1], 'rb') as key_file, open(sys.argv[2], 'rb') as encrypted, open("decrypted_shellcode.bin", 'wb') as out:
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key_size = os.path.getsize(sys.argv[1]) # 0x20
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key = key_file.read(key_size)
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S, j = key_schedule(key)
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"""
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A normal RC4 stream algorithm
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resets j before a second use.
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"""
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# j = 0
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i = 0
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shellcode_size = os.path.getsize(sys.argv[2]) # 0x65E4
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while (shellcode_size > 0):
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char = encrypted.read(1)
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i = (i + 1) % 256
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j = (j + S[i]) % 256
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# swap
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S[i], S[j] = S[j], S[i]
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k = S[(S[i] + S[j]) % 256]
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shellcode_size -= 1
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out.write(chr(ord(char) ^ k))
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out.close()
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key_file.close()
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encrypted.close()
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