unity3d.py

from array import array

with open("Assembly-CSharp.dll", "rb") as encrypted_file:
    data = encrypted_file.read()
key = "*********"

S = list(range(256))
j = 0
out = []

#KSA Phase
for i in range(256):
    j = (j + S[i] + ord( key[i % len(key)] )) % 256
    S[i] , S[j] = S[j] , S[i]

#PRGA Phase
i = j = 0
for char in data:
    i = ( i + 1 ) % 256
    j = ( j + S[i] ) % 256
    S[i] , S[j] = S[j] , S[i]
    out.append(char ^ S[(S[i] + S[j]) % 256])

decrypted_text = array('B', out)
with open('Assembly-CSharp2.dll', 'wb') as decrypted_file:
    decrypted_file.write(decrypted_text)