Fix PDF decryption of ancient 40-bit RC4 with R=2
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@ -99,4 +99,4 @@ This is v10.0.9, a release candidate for v10.1.0. I don't expect there to be maj
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## Fixes on master (not yet released):
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- (none)
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- Fix a bug where decrypting a 40-bit RC4 pdf with R=2 didn't work.
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@ -1369,11 +1369,12 @@ class PDFDocument(object):
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keylen = len(key)
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iv = bytes([0x00]*keylen)
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aes = AES.new(key, AES.MODE_CBC, iv)
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if not encrypt:
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plaintext = AES.new(key,AES.MODE_CBC,iv, True).decrypt(data)
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plaintext = aes.decrypt(data)
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return plaintext
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else:
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aes = AES.new(key, AES.MODE_CBC, iv, False)
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new_data = bytes(data * repetitions)
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crypt = aes.encrypt(new_data)
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return crypt
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@ -1478,14 +1479,23 @@ class PDFDocument(object):
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EncMetadata = b'True'
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if (EncMetadata == ('False' or 'false') or V < 4) and R >= 4:
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hash.update(codecs.decode(b'ffffffff','hex'))
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# Finish hash:
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hash = hash.digest()
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if R >= 3:
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# 8
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for _ in range(50):
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hash = hashlib.md5(hash.digest()[:length//8])
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key = hash.digest()[:length//8]
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hash = hashlib.md5(hash[:length//8]).digest()
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if R == 2:
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# R=2 only uses first five bytes.
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key = hash[:5]
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else:
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key = hash[:length//8]
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if R == 2:
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# Algorithm 3.4
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u1 = ARC4.new(key).decrypt(password)
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u1 = ARC4.new(key).decrypt(self.PASSWORD_PADDING)
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elif R >= 3:
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# Algorithm 3.5
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hash = hashlib.md5(self.PASSWORD_PADDING) # 2
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@ -1498,6 +1508,7 @@ class PDFDocument(object):
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k = b''.join(bytes([c ^ i]) for c in key )
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x = ARC4.new(k).decrypt(x)
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u1 = x+x # 32bytes total
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if R == 2:
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is_authenticated = (u1 == U)
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else:
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