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Create decrypt_darkshell.py #2

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16 changes: 16 additions & 0 deletions decrypt_darkshell.py
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Original file line number Diff line number Diff line change
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def decrypt_darkshell(cipherbytes, start_idx=0x04, stop_idx=0xA8):
"""
De-obfuscates Darkshell comms encoded using the following method:
cipherbyte = 0xDE - [plainbyte - (plainbyte & 0x10) << 1]
The obfuscation is reversed as follows:
intermediate = 0xDE - cipherbyte
plainbyte = intermediate + (intermediate & 0x10) << 1
"""
len_mesg = len(cipherbytes)
if len_mesg != 260:
raise RuntimeError("Darkshell bot-to-CnC comms are always 260 bytes")
plainbytes = []
for cipherbyte in cipherbytes[start_idx:stop_idx]:
intermediate= 0xDE - ord(cipherbyte)
plainbytes += [chr(intermediate + ((intermediate & 0x10) << 1))]
return cipherbytes[:start_idx] + ''.join(plainbytes) + cipherbytes[stop_idx:]