Patch #698833: Support file decryption in zipfile.
diff --git a/Lib/test/test_zipfile.py b/Lib/test/test_zipfile.py
index 54684f3..2d206df 100644
--- a/Lib/test/test_zipfile.py
+++ b/Lib/test/test_zipfile.py
@@ -349,8 +349,49 @@
# and report that the first file in the archive was corrupt.
self.assertRaises(RuntimeError, zipf.testzip)
+
+class DecryptionTests(unittest.TestCase):
+ # This test checks that ZIP decryption works. Since the library does not
+ # support encryption at the moment, we use a pre-generated encrypted
+ # ZIP file
+
+ data = (
+ 'PK\x03\x04\x14\x00\x01\x00\x00\x00n\x92i.#y\xef?&\x00\x00\x00\x1a\x00'
+ '\x00\x00\x08\x00\x00\x00test.txt\xfa\x10\xa0gly|\xfa-\xc5\xc0=\xf9y'
+ '\x18\xe0\xa8r\xb3Z}Lg\xbc\xae\xf9|\x9b\x19\xe4\x8b\xba\xbb)\x8c\xb0\xdbl'
+ 'PK\x01\x02\x14\x00\x14\x00\x01\x00\x00\x00n\x92i.#y\xef?&\x00\x00\x00'
+ '\x1a\x00\x00\x00\x08\x00\x00\x00\x00\x00\x00\x00\x01\x00 \x00\xb6\x81'
+ '\x00\x00\x00\x00test.txtPK\x05\x06\x00\x00\x00\x00\x01\x00\x01\x006\x00'
+ '\x00\x00L\x00\x00\x00\x00\x00' )
+
+ plain = 'zipfile.py encryption test'
+
+ def setUp(self):
+ fp = open(TESTFN, "wb")
+ fp.write(self.data)
+ fp.close()
+ self.zip = zipfile.ZipFile(TESTFN, "r")
+
+ def tearDown(self):
+ self.zip.close()
+ os.unlink(TESTFN)
+
+ def testNoPassword(self):
+ # Reading the encrypted file without password
+ # must generate a RunTime exception
+ self.assertRaises(RuntimeError, self.zip.read, "test.txt")
+
+ def testBadPassword(self):
+ self.zip.setpassword("perl")
+ self.assertRaises(RuntimeError, self.zip.read, "test.txt")
+
+ def testGoodPassword(self):
+ self.zip.setpassword("python")
+ self.assertEquals(self.zip.read("test.txt"), self.plain)
+
def test_main():
- run_unittest(TestsWithSourceFile, TestZip64InSmallFiles, OtherTests, PyZipFileTests)
+ run_unittest(TestsWithSourceFile, TestZip64InSmallFiles, OtherTests,
+ PyZipFileTests, DecryptionTests)
#run_unittest(TestZip64InSmallFiles)
if __name__ == "__main__":
diff --git a/Lib/zipfile.py b/Lib/zipfile.py
index 5c3fff3..93a0b75 100644
--- a/Lib/zipfile.py
+++ b/Lib/zipfile.py
@@ -296,6 +296,65 @@
extra = extra[ln+4:]
+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.
@@ -330,6 +389,7 @@
self.filelist = [] # List of ZipInfo instances for archive
self.compression = compression # Method of compression
self.mode = key = mode.replace('b', '')[0]
+ self.pwd = None
# Check if we were passed a file-like object
if isinstance(file, basestring):
@@ -461,7 +521,11 @@
"""Return the instance of ZipInfo given 'name'."""
return self.NameToInfo[name]
- def read(self, 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"'
@@ -469,6 +533,13 @@
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.header_offset, 0)
@@ -489,6 +560,18 @@
zinfo.orig_filename, fname)
bytes = self.fp.read(zinfo.compress_size)
+ # 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
self.fp.seek(filepos, 0)
if zinfo.compress_type == ZIP_STORED:
pass