Path: csiph.com!news.swapon.de!fu-berlin.de!uni-berlin.de!not-for-mail From: Peter Otten <__peter__@web.de> Newsgroups: comp.lang.python Subject: Re: How to XOR a byte output? Date: Thu, 14 Apr 2016 11:16:53 +0200 Organization: None Lines: 54 Message-ID: References: <387506b1-b645-4907-a45c-81a8c3043099@googlegroups.com> <874mb5twha.fsf@elektro.pacujo.net> <2566ab7f-12bd-4f3b-92b2-45104b8b7dd8@googlegroups.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7Bit X-Trace: news.uni-berlin.de 16/UJ6lOl/PyuV2QP10o+waQKwE43hcTKzMLrYAygdxg== Return-Path: X-Original-To: python-list@python.org Delivered-To: python-list@mail.python.org X-Spam-Status: OK 0.000 X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'modify': 0.04; 'encoded': 0.05; 'utf-8': 0.07; 'subject:How': 0.09; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'xor': 0.09; 'encoding': 0.15; 'explicitly': 0.15; "'hello": 0.16; '127': 0.16; 'codec': 0.16; 'decode': 0.16; 'received:80.91.229.3': 0.16; 'received:dip0.t-ipconnect.de': 0.16; 'received:io': 0.16; 'received:plane.gmane.org': 0.16; 'received:psf.io': 0.16; 'received:t-ipconnect.de': 0.16; 'wrote:': 0.16; 'byte': 0.18; 'bytes': 0.18; '>>>': 0.20; '"",': 0.22; 'code.': 0.23; 'errors': 0.23; '(most': 0.24; 'skip:b 30': 0.24; 'header:User-Agent:1': 0.26; 'example': 0.26; 'header:X-Complaints-To:1': 0.26; 'error': 0.27; 'sequence': 0.27; 'values': 0.28; 'looks': 0.29; 'character': 0.29; 'starts': 0.29; 'code': 0.30; 'error.': 0.31; 'certain': 0.31; 'another': 0.32; "can't": 0.32; 'traceback': 0.33; 'file': 0.34; 'fail': 0.35; 'maps': 0.35; 'but': 0.36; 'there': 0.36; 'to:addr:python-list': 0.36; 'subject:?': 0.36; 'subject:: ': 0.37; 'received:org': 0.37; 'hi,': 0.38; 'to:addr:python.org': 0.40; 'still': 0.40; 'received:de': 0.40; 'skip:u 10': 0.61; 'default': 0.61; 'here': 0.66; 'choose': 0.68; 'gotten': 0.76; 'lone': 0.91 X-Injected-Via-Gmane: http://gmane.org/ X-Gmane-NNTP-Posting-Host: p57bd859e.dip0.t-ipconnect.de User-Agent: KNode/4.13.3 X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: General discussion list for the Python programming language List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-Mailman-Original-Message-ID: X-Mailman-Original-References: <387506b1-b645-4907-a45c-81a8c3043099@googlegroups.com> <874mb5twha.fsf@elektro.pacujo.net> <2566ab7f-12bd-4f3b-92b2-45104b8b7dd8@googlegroups.com> Xref: csiph.com comp.lang.python:106986 durgadevi1 wrote: > >> >> This looks clearer: >> >> >>> code = b'a0\xed\xf0Z\x15]g^\xce3x' >> >>> key = b')U\x81\x9c55*\x08,\xa2WY' >> >>> bytes(c ^ k for c, k in zip(code, key)).decode() >> 'Hello world!' >> >> >> Marko > > Hi, I have gotten another error message when working with the bytes(c ^ k > for c, k in zip(code, key)).decode(). > > Here is the error. > print(bytes(c ^ k for c, k in zip(CODE, key)).decode()) > UnicodeDecodeError: 'utf-8' codec can't decode byte 0x85 in position 0: > invalid start byte > > What I did is XOR the CODE with a certain value before using the > > bytes(c ^ k for c, k in zip(CODE, key)).decode() code. > > However, I get no errors when using values 0 to 127 to XOR with CODE. But > I get errors when using values (128 to 255). May I know how I can modify > the program code so that i can XOR with values (128 to 255)? By default bytes.decode() interprets the sequence of bytes as UTF-8. This will fail if for example there is a lone 0x85 because no encoded character in UTF-8 starts with that byte: >>> code = b'a0\xed\xf0Z\x15]g^\xce3x' >>> key = b'\xe4U\x81\x9c55*\x08,\xa2WY' >>> decrypted = bytes(c^k for c, k in zip(code, key)) >>> decrypted b'\x85ello world!' >>> decrypted.decode() Traceback (most recent call last): File "", line 1, in UnicodeDecodeError: 'utf-8' codec can't decode byte 0x85 in position 0: invalid start byte If you explicitly choose an encoding that maps every single byte to exactly one character (e. g. ISO-8859-15), >>> decrypted.decode("iso-8859-15") '\x85ello world!' the conversion cannot fail -- but the result may still not make sense.