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emdivi_string_decryptor_pe.py
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emdivi_string_decryptor_pe.py
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#
# LICENSE
# Please refer to the LICENSE.txt in the https://github.com/JPCERTCC/aa-tools/
#
import argparse
import pefile
import struct
import re
import sys, os
from hashlib import md5
from Crypto.Cipher import AES
EMDIVI_KEY_PATTERNS = [re.compile(".*\xC7\x04\$(....)\xE8....\x6A\xFF\x53\x8D\x75\xD4\xC6\x45\xFC\x01.*", re.DOTALL),
re.compile(".*\xC7\x04\$(....)\xE8....\xC6\x45\xFC\x01\x8B\x48\x04.*", re.DOTALL),
re.compile(".*\xC7\x04\$(....)\xE8....\x6A\x00\x50\x83\xC8\xFF\x8D\x75\xD4\xC6\x45\xFC\x01.*", re.DOTALL),
re.compile(".*\x68(....)\x33\xC9\x8D\x55.\xE8....\x83\xC4\x10\x6A\xFF\x53\x8D\x75\xD4.*", re.DOTALL),
re.compile(".*\x68(....)\x33\xC9\x8D\x55.\xE8....\x83\xC4\x20\xC6\x45.\x01.*", re.DOTALL),
re.compile(".*\x68(....)\x33\xC0\x8D\xBD.\xFF\xFF\xFF\x8D\x8D.*", re.DOTALL)]
def mask32bit(input_dword):
return input_dword & 0xffffffff
def get_key(version, pe):
base_addr = pe.OPTIONAL_HEADER.ImageBase + pe.sections[0].VirtualAddress
pe_data = pe.get_memory_mapped_image()
data = pe_data[base_addr - pe.OPTIONAL_HEADER.ImageBase:base_addr - pe.OPTIONAL_HEADER.ImageBase + 0x20000]
key_str = None
for pattern in EMDIVI_KEY_PATTERNS:
m = re.match(pattern, data)
if m:
offset = struct.unpack("I", m.group(1))[0]
key_str = pe_data[offset - pe.OPTIONAL_HEADER.ImageBase:offset - pe.OPTIONAL_HEADER.ImageBase + 0x1000]
key_str = key_str.split("\x00")[0]
break
if key_str == None:
print "[!] could not find base key string!"
return False
key = md5(md5(version.encode("base64").strip("\n")).hexdigest() + md5(key_str).hexdigest()).digest()
if version[:3] == "t19" or (version[:3] == "t20" and (int(version[4:6]) >= 7 and int(version[4:6]) < 26)):
tmp = ""
for i, c in enumerate(key.encode('hex')):
tmp += chr(ord(c) + i)
tmp = [tmp[i:i+6] for i in xrange(0, len(tmp), 6)][:4]
key = ""
for s in tmp:
pattern = re.compile("^[0-9,a-f,A-F]+")
m = re.match(pattern, s)
if m:
key += struct.pack(">I", int(m.group(0), 16))
else:
key += struct.pack(">I", 0)
elif version[:3] == "t20" and (int(version[4:6]) >= 26 or int(version[4:6]) < 7):
tmp = ""
for i, c in enumerate(key.encode('hex')):
tmp += chr(ord(c) + i)
key = tmp[:24]
return key
def get_encrypted_data(pe):
pe_data = pe.get_memory_mapped_image()
encrypted_data = []
# get encrypted base64 strings
# skip past PE header, make sure strings are at least length 64
for m in re.finditer(r"([0-9a-zA-Z\+\/]+={,2})", pe_data[pe.sections[0].VirtualAddress:]):
try:
data = m.groups()[0].decode("base64")
except:
continue
if len(data) >= 8:
encrypted_data.append((m.start() + pe.OPTIONAL_HEADER.ImageBase, data))
for s in pe.sections:
if s.Name.startswith(".rdata"):
addr = pe.OPTIONAL_HEADER.ImageBase + s.VirtualAddress
data = s.get_data()
i = 0
while i < len(data):
push = "\x68{}".format(struct.pack("<I", addr + i))
if pe_data.find(push) != -1:
c_str = data[i:i+data[i:].find("\x00")]
if c_str:
try:
c_str.encode("ascii")
i += len(c_str)
continue
except UnicodeDecodeError, e:
pass
enc_strlen = data[i:].find("\x00\x00\x00\x00")
enc_str = data[i:i+enc_strlen]
encrypted_data.append((addr + i, enc_str))
i += enc_strlen + 4
else:
i += 1
return encrypted_data
def xxtea_decrypt(key, input_str):
input_dword = [struct.unpack("<I", input_str[i:i+4])[0] for i in xrange(0, len(input_str), 4)]
key_dword = struct.unpack(">4I", key)
last = input_dword[0]
data1 = mask32bit((0x9E3779B9 * (52 / len(input_dword) + 6)))
while True:
idx2 = (data1 >> 2) & 3
for idx in xrange(len(input_dword)-1, 0, -1):
work1 = (input_dword[idx - 1] >> 5) ^ mask32bit(4 * last)
work2 = mask32bit(16 * input_dword[idx - 1] ^ (last >> 3))
work3 = mask32bit((data1 ^ last) + (input_dword[idx -1] ^ key_dword[idx2 ^ (idx & 3)]))
work = mask32bit(work3 ^ work2 + work1)
input_dword[idx] = mask32bit(input_dword[idx] - work)
last = input_dword[idx]
work1 = mask32bit((input_dword[-1] >> 5) ^ (last * 4))
work2 = mask32bit((16 * input_dword[-1]) ^ (last >> 3))
work = mask32bit(data1 ^ last) + mask32bit(input_dword[-1] ^ key_dword[idx2]) ^ mask32bit(work2 + work1)
input_dword[0] = mask32bit(input_dword[0] - work)
last = input_dword[0]
data1 = mask32bit(data1 - 0x9E3779B9)
if data1 == 0:
break
out = "".join([struct.pack("<I", input_dword[i]) for i in xrange(len(input_dword))])
return out
def xxtea_encrypt(key, input_str):
input_dwords = [struct.unpack("<I", input_str[i:i+4])[0] for i in xrange(0, len(input_str), 4)]
key_dword = struct.unpack(">4I", key)
out = ""
for i in range(0, len(input_dwords), 4):
input_dword = input_dwords[i:i+4]
data1 = 0
count = 52 / len(input_dword) + 6
while count > 0:
count -= 1
data1 = mask32bit(data1 + 0x9E3779B9)
last = input_dword[-1]
idx2 = (data1 >> 2) & 3
for idx in xrange(1, len(input_dword)):
work1 = mask32bit((last >> 5) ^ (4 * input_dword[idx]))
work2 = mask32bit((16 * last) ^ (input_dword[idx] >> 3))
work3 = mask32bit((data1 ^ input_dword[idx]) + (last ^ key_dword[idx2^((idx-1)&3)]))
input_dword[idx-1] = mask32bit(input_dword[idx-1] + (work3 ^ (work2 + work1)))
last = input_dword[idx-1]
work1 = mask32bit((last >> 5) ^ (4 * input_dword[0]))
work2 = mask32bit((16 * last) ^ (input_dword[0] >> 3))
work = mask32bit((data1 ^ input_dword[0]) + (last ^ key_dword[idx2^(idx&3)]))
input_dword[-1] = mask32bit(input_dword[-1] + (work ^ (work1 + work2)))
last = input_dword[-1]
out += "".join([struct.pack("<I", input_dword[j]) for j in xrange(len(input_dword))])
return out
def emdivi_decrypt(input_str, key, version):
salt = "\x10"*16
if version[:3] == "t17":
dec = xxtea_decrypt(key, input_str)
elif version[:3] == "t19" or (version[:3] == "t20" and (int(version[4:6]) >= 7 and int(version[4:6]) < 26)):
tmp = xxtea_encrypt(key, salt + input_str)
dec = ""
for i in xrange(0, len(input_str)):
dec += chr(ord(tmp[i]) ^ ord(input_str[i]))
elif version[:3] == "t20" and (int(version[4:6]) >= 26 or int(version[4:6]) < 7):
aes = AES.new(key)
tmp = aes.encrypt(salt + input_str[:-len(salt)])
dec = ""
for i in xrange(0, len(input_str)):
dec += chr(ord(tmp[i]) ^ ord(input_str[i]))
dec = dec[:-ord(dec[-1])]
out = range(0, len(dec))
for i in xrange(0, len(dec)):
if i & 1:
out[i] = (ord(dec[i]) + i - len(dec)) % 256
else:
out[i] = (ord(dec[i]) + len(dec) - i) % 256
result = "".join(map(chr, out))
if out[-1] <= len(result) and result[-out[-1]:] == (result[-1] * out[-1]):
result = result[:-out[-1]]
return result
def main():
parser = argparse.ArgumentParser(description="Emdivi string decryptor")
parser.add_argument("filename", metavar="FILE", help="PE file")
parser.add_argument("version", metavar="VERSION", help="Version string from emdivi")
args = parser.parse_args()
print "[*] start Emdivi string decryptor"
pe = pefile.PE(args.filename)
version = args.version
print 'version: "%s"' % version
if version[0] != 't' or int(version[1:3]) < 17 or int(version[1:3] > 21):
"[*] unknown version!"
print "[*] calculating encryption key"
key = get_key(version, pe)
if key == False:
return
print 'encryption key: %s' % key.encode('hex')
print "[*] listing up encrypted strings/data"
encrypted_data = get_encrypted_data(pe)
if len(encrypted_data) == 0:
print "[!] could not find encrypted strings/data!"
return
print "[*] decrypting..."
for addr, enc in encrypted_data:
try:
decoded_str = emdivi_decrypt(enc, key, version)
if decoded_str:
decoded_str.decode('ascii')
print '0x%08x: "%s"' % (addr, decoded_str)
#MakeRptCmt(addr, '"'+decoded_str+'"')
except:
#print "[!] error: %08x, %s" % (addr, enc)
pass
print "[*] end Emdivi string decryptor\n"
if __name__ == "__main__":
main()