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   1  # shop-js encrypted message decoder in Python
   2  # Copyright John Hanna (c) 2002 under the terms of the GPL
   3  # see http://shop-js.sf.net for details and latest version
   4  
   5  debug=0
   6  
   7  import privateKey
   8  import sys
   9  
  10  def rc4(key, string):
  11      """Return string rc4 (de/en)crypted with RC4."""
  12      s,i,j,klen=range(256),0,0,len(key)
  13      for i in range(256):
  14          j=(ord(key[i%klen])+s[i]+j)%256
  15          s[i],s[j]=s[j],s[i]
  16      for i in range(256):
  17          j=(ord(key[i%klen])+s[i]+j)%256
  18          s[i],s[j]=s[j],s[i]
  19      r=''
  20      for i in range(len(string)):
  21          i2=i % 256
  22          j=(s[i2]+j)%256
  23          s[i2],s[j]=s[j],s[i2]
  24          r+=chr(ord(string[i])^s[(s[i2]+s[j])%256])
  25      return r
  26  
  27  def inverse(x, n):
  28       """Return the mod n inverse of x."""
  29       y, a, b = n, 1, 0
  30       while y>0:
  31           x, (q, y) = y, divmod(x, y)
  32           a, b = b, a - b*q
  33       if a < 0:
  34           a = a + n
  35       assert x==1, "No inverse, GCD is %d" % x
  36       return a
  37  
  38  
  39  def crt_RSA(m, d, p, q):
  40       """ Compute m**d mod p*q for RSA private key operations."""
  41       xp = pow(m % p, d%(p-1), p)
  42       xq = pow(m % q, d%(q-1), q)
  43       t = ((xq - xp) * inverse(p, q)) % q
  44       if t < 0:
  45           t = t + q
  46       return t * p + xp
  47  
  48  
  49  b64s='abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_"'
  50  def base64ToText(text):
  51      r,m,a,c='',0,0,0
  52      for i in text[:]:
  53          c=b64s.find(i)
  54          if(c >= 0) :
  55               if(m):
  56                     r += chr((c << (8-m))& 255 | a)
  57               a = c >> m
  58               m+=2
  59               if(m==8):m=0
  60      return r
  61  
  62  def t2b(s):
  63      r=0L
  64      m=1L
  65      for i in s[:]:
  66          r+=m*ord(i)
  67          m*=256L
  68      return r
  69  
  70  def b2t(b):
  71      r=''
  72      while(b):
  73          r+=chr(b % 256)
  74          b>>=8
  75      return r
  76  
  77  def fix(a):
  78      r=0L
  79      s=0
  80      for i in a[:]:
  81          r|=long(i) << s
  82          s+=28
  83      return r
  84  
  85  def rsaDecode(key, text):
  86      """ decode the text based on the given rsa key. """
  87      # separate the session key from the text
  88      text=base64ToText(text)
  89      sessionKeyLength=ord(text[0])
  90      sessionKeyEncryptedText=text[1:sessionKeyLength+1]
  91      text=text[sessionKeyLength+1:]
  92      sessionKeyEncrypted=t2b(sessionKeyEncryptedText)
  93  
  94      # un-rsa the session key
  95      sessionkey=crt_RSA(sessionKeyEncrypted,fix(key[0]),fix(key[1]),fix(key[2]))
  96      #sessionkey=crt_RSA(sessionKeyEncrypted,fix(d),fix(p),fix(q))
  97      sessionkey=b2t(sessionkey)
  98  
  99      text=rc4(sessionkey,text)
 100      return text
 101  
 102  if  debug:
 103       message=rsaDecode(privateKey.value, sys.argv[1])
 104       print "Debug :"
 105       print message
 106  
 107  else:
 108      print rsaDecode(privateKey.value, sys.argv[1])
 109