反转加密与凯撒加密 python实现

基础的反转加密法
就是将前后反转，这是最基础的加密方法
《python密码学编程》 Hacking Secret Ciphers with Python

#基础的反转加密法#就是将前后反转，这是最基础的加密方法#《python密码学编程》 Hacking Secret Ciphers with Pythonmessage = 'Three can keep secret, if two of them are dead.'translated = ' 'i = len(message) - 1while i >= 0:    translated = translated + message[i]    i = i -1print(translated)

一步步跟踪

#基础的反转加密法#就是将前后反转，这是最基础的加密方法#《python密码学编程》 Hacking Secret Ciphers with Pythonmessage = 'Three can keep secret, if two of them are dead.'translated = ' 'i = len(message) - 1while i >= 0:    translated = translated + message[i]    print(i,message[i],translated)    i = i -1print(translated)

凯撒加密法

在密码学中，恺撒密码是一种最简单且最广为人知的加密技术。它是一种替换加密的技术，明文中的所有字母都在字母表上向后（或向前）按照一个固定数目进行偏移后被替换成密文。例，当偏移量是3的时候，所有的字母A将被替换成D，B变成E，以此类推。这个加密方法是以恺撒的名字命名的，当年恺撒曾用此方法与其将军们进行联系。 恺撒密码通常被作为其他更复杂的加密方法中的一个步骤。恺撒密码还在现代的ROT13系统中被应用。但是和所有的利用字母表进行替换的加密技术一样，恺撒密码非常容易被破解，而且在实际应用中也无法保证通信安全。

“恺撒密码”据传是古罗马恺撒大帝用来保护重要军情的加密系统。它是一种替代密码，通过将字母按顺序推后起3位起到加密作用，如将字母A换作字母D，将字母B换作字母E。据说恺撒是率先使用加密函的古代将领之一，因此这种加密方法被称为恺撒密码。
假如有这样一条指令：
RETURN TO ROME
用恺撒密码加密后就成为：
UHWXUA WR URPH
如果这份指令被敌方截获，也将不会泄密，因为字面上看不出任何意义。
这种加密方法还可以依据移位的不同产生新的变化，如将每个字母左19位，就产生这样一个明密对照表：
明:A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
密:T U V W X Y Z A B C D E F G H I J K L M N O P Q R S
在这个加密表下，明文与密文的对照关系就变成：
明文：THE FAULT, DEAR BRUTUS, LIES NOT IN OUR STARS BUT IN OURSELVES.
密文：MAX YTNEM, WXTK UKNMNL, EBXL GHM BG HNK LMTKL UNM BG HNKLXEOXL.

#Caesar Cipher#需要pyperclip.pyimport pyperclipmessage = 'this is my secret message.'key = 13mode = 'encrypt'LETTERS = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'translated = ''message = message.upper()for symbol in message:    if symbol in LETTERS:        num = LETTERS.find(symbol)        if mode == 'encrypt':            num = num + key        elif mode == 'decrypt':            num = num - key        if num  >=len(LETTERS):            num = num - len(LETTERS)        elif num < 0:            num = num + len(LETTERS)        translated= translated + LETTERS[num]    else:        translated = translated +symbolprint(translated)pyperclip.copy(translated)

"""PyperclipA cross-platform clipboard module for Python. (only handles plain text for now)By Al Sweigart [e-mail] LicenseUsage:  import pyperclip  pyperclip.copy('The text to be copied to the clipboard.')  spam = pyperclip.paste()  if not pyperclip.copy:    print("Copy functionality unavailable!")On Windows, no additional modules are needed.On Mac, the module uses pbcopy and pbpaste, which should come with the os.On Linux, install xclip or xsel via package manager. For example, in Debian:sudo apt-get install xclipOtherwise on Linux, you will need the gtk or PyQt4 modules installed.gtk and PyQt4 modules are not available for Python 3,and this module does not work with PyGObject yet."""__version__ = '1.5.27'import platformimport osimport subprocessimport sysEXCEPT_MSG = """    Pyperclip could not find a copy/paste mechanism for your system.    For more information, please visit https://pyperclip.readthedocs.io/en/latest/introduction.html#not-implemented-error"""PY2 = sys.version_info[0] == 2if PY2:  text_type = unicodeelse:  text_type = strdef init_osx_clipboard():    def copy_osx(text):        p = subprocess.Popen(['pbcopy', 'w'],                             stdin=subprocess.PIPE, close_fds=True)        p.communicate(input=text.encode('utf-8'))    def paste_osx():        p = subprocess.Popen(['pbpaste', 'r'],                             stdout=subprocess.PIPE, close_fds=True)        stdout, stderr = p.communicate()        return stdout.decode('utf-8')    return copy_osx, paste_osxdef init_gtk_clipboard():    import gtk    def copy_gtk(text):        global cb        cb = gtk.Clipboard()        cb.set_text(text)        cb.store()    def paste_gtk():        clipboardContents = gtk.Clipboard().wait_for_text()        # for python 2, returns None if the clipboard is blank.        if clipboardContents is None:            return ''        else:            return clipboardContents    return copy_gtk, paste_gtkdef init_qt_clipboard():    # $DISPLAY should exist    from PyQt4.QtGui import QApplication    app = QApplication([])    def copy_qt(text):        cb = app.clipboard()        cb.setText(text)    def paste_qt():        cb = app.clipboard()        return text_type(cb.text())    return copy_qt, paste_qtdef init_xclip_clipboard():    def copy_xclip(text):        p = subprocess.Popen(['xclip', '-selection', 'c'],                             stdin=subprocess.PIPE, close_fds=True)        p.communicate(input=text.encode('utf-8'))    def paste_xclip():        p = subprocess.Popen(['xclip', '-selection', 'c', '-o'],                             stdout=subprocess.PIPE, close_fds=True)        stdout, stderr = p.communicate()        return stdout.decode('utf-8')    return copy_xclip, paste_xclipdef init_xsel_clipboard():    def copy_xsel(text):        p = subprocess.Popen(['xsel', '-b', '-i'],                             stdin=subprocess.PIPE, close_fds=True)        p.communicate(input=text.encode('utf-8'))    def paste_xsel():        p = subprocess.Popen(['xsel', '-b', '-o'],                             stdout=subprocess.PIPE, close_fds=True)        stdout, stderr = p.communicate()        return stdout.decode('utf-8')    return copy_xsel, paste_xseldef init_klipper_clipboard():    def copy_klipper(text):        p = subprocess.Popen(            ['qdbus', 'org.kde.klipper', '/klipper', 'setClipboardContents',             text.encode('utf-8')],            stdin=subprocess.PIPE, close_fds=True)        p.communicate(input=None)    def paste_klipper():        p = subprocess.Popen(            ['qdbus', 'org.kde.klipper', '/klipper', 'getClipboardContents'],            stdout=subprocess.PIPE, close_fds=True)        stdout, stderr = p.communicate()        # Workaround for https://bugs.kde.org/show_bug.cgi?id=342874        # TODO: https://github.com/asweigart/pyperclip/issues/43        clipboardContents = stdout.decode('utf-8')        # even if blank, Klipper will append a newline at the end        assert len(clipboardContents) > 0        # make sure that newline is there        assert clipboardContents.endswith('\n')        if clipboardContents.endswith('\n'):            clipboardContents = clipboardContents[:-1]        return clipboardContents    return copy_klipper, paste_klipperdef init_no_clipboard():    class ClipboardUnavailable(object):        def __call__(self, *args, **kwargs):            raise PyperclipException(EXCEPT_MSG)        if PY2:            def __nonzero__(self):                return False        else:            def __bool__(self):                return False    return ClipboardUnavailable(), ClipboardUnavailable()"""This module implements clipboard handling on Windows using ctypes."""import timeimport contextlibimport ctypesfrom ctypes import c_size_t, sizeof, c_wchar_p, get_errno, c_wcharclass CheckedCall(object):    def __init__(self, f):        super(CheckedCall, self).__setattr__("f", f)    def __call__(self, *args):        ret = self.f(*args)        if not ret and get_errno():            raise PyperclipWindowsException("Error calling " + self.f.__name__)        return ret    def __setattr__(self, key, value):        setattr(self.f, key, value)def init_windows_clipboard():    from ctypes.wintypes import (HGLOBAL, LPVOID, DWORD, LPCSTR, INT, HWND,                                 HINSTANCE, HMENU, BOOL, UINT, HANDLE)    windll = ctypes.windll    safeCreateWindowExA = CheckedCall(windll.user32.CreateWindowExA)    safeCreateWindowExA.argtypes = [DWORD, LPCSTR, LPCSTR, DWORD, INT, INT,                                    INT, INT, HWND, HMENU, HINSTANCE, LPVOID]    safeCreateWindowExA.restype = HWND    safeDestroyWindow = CheckedCall(windll.user32.DestroyWindow)    safeDestroyWindow.argtypes = [HWND]    safeDestroyWindow.restype = BOOL    OpenClipboard = windll.user32.OpenClipboard    OpenClipboard.argtypes = [HWND]    OpenClipboard.restype = BOOL    safeCloseClipboard = CheckedCall(windll.user32.CloseClipboard)    safeCloseClipboard.argtypes = []    safeCloseClipboard.restype = BOOL    safeEmptyClipboard = CheckedCall(windll.user32.EmptyClipboard)    safeEmptyClipboard.argtypes = []    safeEmptyClipboard.restype = BOOL    safeGetClipboardData = CheckedCall(windll.user32.GetClipboardData)    safeGetClipboardData.argtypes = [UINT]    safeGetClipboardData.restype = HANDLE    safeSetClipboardData = CheckedCall(windll.user32.SetClipboardData)    safeSetClipboardData.argtypes = [UINT, HANDLE]    safeSetClipboardData.restype = HANDLE    safeGlobalAlloc = CheckedCall(windll.kernel32.GlobalAlloc)    safeGlobalAlloc.argtypes = [UINT, c_size_t]    safeGlobalAlloc.restype = HGLOBAL    safeGlobalLock = CheckedCall(windll.kernel32.GlobalLock)    safeGlobalLock.argtypes = [HGLOBAL]    safeGlobalLock.restype = LPVOID    safeGlobalUnlock = CheckedCall(windll.kernel32.GlobalUnlock)    safeGlobalUnlock.argtypes = [HGLOBAL]    safeGlobalUnlock.restype = BOOL    GMEM_MOVEABLE = 0x0002    CF_UNICODETEXT = 13    @contextlib.contextmanager    def window():        """        Context that provides a valid Windows hwnd.        """        # we really just need the hwnd, so setting "STATIC"        # as predefined lpClass is just fine.        hwnd = safeCreateWindowExA(0, b"STATIC", None, 0, 0, 0, 0, 0,                                   None, None, None, None)        try:            yield hwnd        finally:            safeDestroyWindow(hwnd)    @contextlib.contextmanager    def clipboard(hwnd):        """        Context manager that opens the clipboard and prevents        other applications from modifying the clipboard content.        """        # We may not get the clipboard handle immediately because        # some other application is accessing it (?)        # We try for at least 500ms to get the clipboard.        t = time.time() + 0.5        success = False        while time.time() < t:            success = OpenClipboard(hwnd)            if success:                break            time.sleep(0.01)        if not success:            raise PyperclipWindowsException("Error calling OpenClipboard")        try:            yield        finally:            safeCloseClipboard()    def copy_windows(text):        # This function is heavily based on        # http://msdn.com/ms649016#_win32_Copying_Information_to_the_Clipboard        with window() as hwnd:            # http://msdn.com/ms649048            # If an application calls OpenClipboard with hwnd set to NULL,            # EmptyClipboard sets the clipboard owner to NULL;            # this causes SetClipboardData to fail.            # => We need a valid hwnd to copy something.            with clipboard(hwnd):                safeEmptyClipboard()                if text:                    # http://msdn.com/ms649051                    # If the hMem parameter identifies a memory object,                    # the object must have been allocated using the                    # function with the GMEM_MOVEABLE flag.                    count = len(text) + 1                    handle = safeGlobalAlloc(GMEM_MOVEABLE,                                             count * sizeof(c_wchar))                    locked_handle = safeGlobalLock(handle)                    ctypes.memmove(c_wchar_p(locked_handle), c_wchar_p(text), count * sizeof(c_wchar))                    safeGlobalUnlock(handle)                    safeSetClipboardData(CF_UNICODETEXT, handle)    def paste_windows():        with clipboard(None):            handle = safeGetClipboardData(CF_UNICODETEXT)            if not handle:                # GetClipboardData may return NULL with errno == NO_ERROR                # if the clipboard is empty.                # (Also, it may return a handle to an empty buffer,                # but technically that's not empty)                return ""            return c_wchar_p(handle).value    return copy_windows, paste_windowsclass PyperclipException(RuntimeError):    passclass PyperclipWindowsException(PyperclipException):    def __init__(self, message):        message += " (%s)" % ctypes.WinError()        super(PyperclipWindowsException, self).__init__(message)# `import PyQt4` sys.exit()s if DISPLAY is not in the environment.# Thus, we need to detect the presence of $DISPLAY manually# and not load PyQt4 if it is absent.HAS_DISPLAY = os.getenv("DISPLAY", False)CHECK_CMD = "where" if platform.system() == "Windows" else "which"def _executable_exists(name):    return subprocess.call([CHECK_CMD, name],                           stdout=subprocess.PIPE, stderr=subprocess.PIPE) == 0def determine_clipboard():    # Determine the OS/platform and set    # the copy() and paste() functions accordingly.    if 'cygwin' in platform.system().lower():        # FIXME: pyperclip currently does not support Cygwin,        # see https://github.com/asweigart/pyperclip/issues/55        pass    elif os.name == 'nt' or platform.system() == 'Windows':        return init_windows_clipboard()    if os.name == 'mac' or platform.system() == 'Darwin':        return init_osx_clipboard()    if HAS_DISPLAY:        # Determine which command/module is installed, if any.        try:            import gtk  # check if gtk is installed        except ImportError:            pass        else:            return init_gtk_clipboard()        try:            import PyQt4  # check if PyQt4 is installed        except ImportError:            pass        else:            return init_qt_clipboard()        if _executable_exists("xclip"):            return init_xclip_clipboard()        if _executable_exists("xsel"):            return init_xsel_clipboard()        if _executable_exists("klipper") and _executable_exists("qdbus"):            return init_klipper_clipboard()    return init_no_clipboard()def set_clipboard(clipboard):    global copy, paste    clipboard_types = {'osx': init_osx_clipboard,                       'gtk': init_gtk_clipboard,                       'qt': init_qt_clipboard,                       'xclip': init_xclip_clipboard,                       'xsel': init_xsel_clipboard,                       'klipper': init_klipper_clipboard,                       'windows': init_windows_clipboard,                       'no': init_no_clipboard}    copy, paste = clipboard_types[clipboard]()copy, paste = determine_clipboard()__all__ = ["copy", "paste"]

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