*** zipfile_cvs2.py	Thu Mar  6 17:30:30 2003
--- zipfile_encryption.py	Thu Mar  6 17:07:09 2003
***************
*** 168,173 ****
--- 168,232 ----
          return path
  
  
+ class _ZipDecrypter:
+     """Class to handle decryption of files stored within a ZIP archive.
+ 
+     ZIP supports a password-based form of encryption. Even though known
+     plaintext attacks have been found against it, it is still useful
+     for low-level securicy.
+ 
+     Usage:
+         zd = _ZipDecrypter(mypwd)
+         plain_char = zd(cypher_char)
+         plain_text = map(zd, cypher_text)
+     """
+  
+     def _GenerateCRCTable():
+         """Generate a CRC-32 table.
+ 
+         ZIP encryption uses the CRC32 one-byte primitive for scrambling some
+         internal keys. We noticed that a direct implementation is faster than
+         relying on binascii.crc32().
+         """
+         poly = 0xedb88320
+         table = [0] * 256
+         for i in range(256):
+             crc = i
+             for j in range(8):
+                 if crc & 1:
+                     crc = ((crc >> 1) & 0x7FFFFFFF) ^ poly
+                 else:
+                     crc = ((crc >> 1) & 0x7FFFFFFF)
+             table[i] = crc
+         return table
+     crctable = _GenerateCRCTable()
+ 
+     def _crc32(self, ch, crc):
+         """Compute the CRC32 primitive on one byte."""
+         return ((crc >> 8) & 0xffffff) ^ self.crctable[(crc ^ ord(ch)) & 0xff]
+   
+     def __init__(self, pwd):
+         self.key0 = 305419896
+         self.key1 = 591751049
+         self.key2 = 878082192
+         for p in pwd:
+             self._UpdateKeys(p)
+ 
+     def _UpdateKeys(self, c):
+         self.key0 = self._crc32(c, self.key0)
+         self.key1 = (self.key1 + (self.key0 & 255)) & 4294967295
+         self.key1 = (self.key1 * 134775813 + 1) & 4294967295
+         self.key2 = self._crc32(chr((self.key1 >> 24) & 255), self.key2)
+     
+     def __call__(self, c):
+         """Decrypt a single character."""
+         c = ord(c)
+         k = self.key2 | 2
+         c = c ^ (((k * (k^1)) >> 8) & 255)
+         c = chr(c)
+         self._UpdateKeys(c)
+         return c
+ 
  class ZipFile:
      """ Class with methods to open, read, write, close, list zip files.
  
***************
*** 196,201 ****
--- 255,261 ----
          self.filelist = []      # List of ZipInfo instances for archive
          self.compression = compression  # Method of compression
          self.mode = key = mode[0]
+         self.pwd = None
  
          # Check if we were passed a file-like object
          if type(file) == type(""):
***************
*** 336,342 ****
          """Return the instance of ZipInfo given 'name'."""
          return self.NameToInfo[name]
  
!     def read(self, name):
          """Return file bytes (as a string) for name."""
          if self.mode not in ("r", "a"):
              raise RuntimeError, 'read() requires mode "r" or "a"'
--- 396,406 ----
          """Return the instance of ZipInfo given 'name'."""
          return self.NameToInfo[name]
  
!     def setpassword(self, pwd):
!         """Set default password for encrypted files."""
!         self.pwd = pwd
!             
!     def read(self, name, pwd=None):
          """Return file bytes (as a string) for name."""
          if self.mode not in ("r", "a"):
              raise RuntimeError, 'read() requires mode "r" or "a"'
***************
*** 344,353 ****
--- 408,436 ----
              raise RuntimeError, \
                    "Attempt to read ZIP archive that was already closed"
          zinfo = self.getinfo(name)
+         is_encrypted = zinfo.flag_bits & 0x1
+         if is_encrypted: 
+             if not pwd:
+                 pwd = self.pwd
+             if not pwd:
+                 raise RuntimeError, "File %s is encrypted, " \
+                       "password required for extraction" % name      
          filepos = self.fp.tell()
          self.fp.seek(zinfo.file_offset, 0)
          bytes = self.fp.read(zinfo.compress_size)
          self.fp.seek(filepos, 0)
+         # Go with decryption
+         if is_encrypted:
+             zd = _ZipDecrypter(pwd)
+             # The first 12 bytes in the cypher stream is an encryption header
+             #  used to strengthen the algorithm. The first 11 bytes are
+             #  completely random, while the 12th contains the MSB of the CRC,
+             #  and is used to check the correctness of the password.
+             h = map(zd, bytes[0:12])
+             if ord(h[11]) != ((zinfo.CRC>>24)&255):
+                 raise RuntimeError, "Bad password for file %s" % name
+             bytes = "".join(map(zd, bytes[12:]))
+         # Go with decompression
          if zinfo.compress_type == ZIP_STORED:
              pass
          elif zinfo.compress_type == ZIP_DEFLATED: