1 #! /usr/bin/env python

     2 

     3 """RFC 3548: Base16, Base32, Base64 Data Encodings"""

     4 

     5 # Modified 04-Oct-1995 by Jack Jansen to use binascii module

     6 # Modified 30-Dec-2003 by Barry Warsaw to add full RFC 3548 support

     7 

     8 import re

     9 import struct

    10 import binascii

    11 

    12 

    13 __all__ = [

    14     # Legacy interface exports traditional RFC 1521 Base64 encodings

    15     'encode', 'decode', 'encodestring', 'decodestring',

    16     # Generalized interface for other encodings

    17     'b64encode', 'b64decode', 'b32encode', 'b32decode',

    18     'b16encode', 'b16decode',

    19     # Standard Base64 encoding

    20     'standard_b64encode', 'standard_b64decode',

    21     # Some common Base64 alternatives.  As referenced by RFC 3458, see thread

    22     # starting at:

    23     #

    24     # http://zgp.org/pipermail/p2p-hackers/2001-September/000316.html

    25     'urlsafe_b64encode', 'urlsafe_b64decode',

    26     ]

    27 

    28 _translation = [chr(_x) for _x in range(256)]

    29 EMPTYSTRING = ''

    30 

    31 

    32 def _translate(s, altchars):

    33     translation = _translation[:]

    34     for k, v in altchars.items():

    35         translation[ord(k)] = v

    36     return s.translate(''.join(translation))

    37 

    38 

    39 

    40 # Base64 encoding/decoding uses binascii

    41 

    42 def b64encode(s, altchars=None):

    43     """Encode a string using Base64.

    44 

    45     s is the string to encode.  Optional altchars must be a string of at least

    46     length 2 (additional characters are ignored) which specifies an

    47     alternative alphabet for the '+' and '/' characters.  This allows an

    48     application to e.g. generate url or filesystem safe Base64 strings.

    49 

    50     The encoded string is returned.

    51     """

    52     # Strip off the trailing newline

    53     encoded = binascii.b2a_base64(s)[:-1]

    54     if altchars is not None:

    55         return _translate(encoded, {'+': altchars[0], '/': altchars[1]})

    56     return encoded

    57 

    58 

    59 def b64decode(s, altchars=None):

    60     """Decode a Base64 encoded string.

    61 

    62     s is the string to decode.  Optional altchars must be a string of at least

    63     length 2 (additional characters are ignored) which specifies the

    64     alternative alphabet used instead of the '+' and '/' characters.

    65 

    66     The decoded string is returned.  A TypeError is raised if s were

    67     incorrectly padded or if there are non-alphabet characters present in the

    68     string.

    69     """

    70     if altchars is not None:

    71         s = _translate(s, {altchars[0]: '+', altchars[1]: '/'})

    72     try:

    73         return binascii.a2b_base64(s)

    74     except binascii.Error, msg:

    75         # Transform this exception for consistency

    76         raise TypeError(msg)

    77 

    78 

    79 def standard_b64encode(s):

    80     """Encode a string using the standard Base64 alphabet.

    81 

    82     s is the string to encode.  The encoded string is returned.

    83     """

    84     return b64encode(s)

    85 

    86 def standard_b64decode(s):

    87     """Decode a string encoded with the standard Base64 alphabet.

    88 

    89     s is the string to decode.  The decoded string is returned.  A TypeError

    90     is raised if the string is incorrectly padded or if there are non-alphabet

    91     characters present in the string.

    92     """

    93     return b64decode(s)

    94 

    95 def urlsafe_b64encode(s):

    96     """Encode a string using a url-safe Base64 alphabet.

    97 

    98     s is the string to encode.  The encoded string is returned.  The alphabet

    99     uses '-' instead of '+' and '_' instead of '/'.

   100     """

   101     return b64encode(s, '-_')

   102 

   103 def urlsafe_b64decode(s):

   104     """Decode a string encoded with the standard Base64 alphabet.

   105 

   106     s is the string to decode.  The decoded string is returned.  A TypeError

   107     is raised if the string is incorrectly padded or if there are non-alphabet

   108     characters present in the string.

   109 

   110     The alphabet uses '-' instead of '+' and '_' instead of '/'.

   111     """

   112     return b64decode(s, '-_')

   113 

   114 

   115 

   116 # Base32 encoding/decoding must be done in Python

   117 _b32alphabet = {

   118     0: 'A',  9: 'J', 18: 'S', 27: '3',

   119     1: 'B', 10: 'K', 19: 'T', 28: '4',

   120     2: 'C', 11: 'L', 20: 'U', 29: '5',

   121     3: 'D', 12: 'M', 21: 'V', 30: '6',

   122     4: 'E', 13: 'N', 22: 'W', 31: '7',

   123     5: 'F', 14: 'O', 23: 'X',

   124     6: 'G', 15: 'P', 24: 'Y',

   125     7: 'H', 16: 'Q', 25: 'Z',

   126     8: 'I', 17: 'R', 26: '2',

   127     }

   128 

   129 _b32tab = _b32alphabet.items()

   130 _b32tab.sort()

   131 _b32tab = [v for k, v in _b32tab]

   132 _b32rev = dict([(v, long(k)) for k, v in _b32alphabet.items()])

   133 

   134 

   135 def b32encode(s):

   136     """Encode a string using Base32.

   137 

   138     s is the string to encode.  The encoded string is returned.

   139     """

   140     parts = []

   141     quanta, leftover = divmod(len(s), 5)

   142     # Pad the last quantum with zero bits if necessary

   143     if leftover:

   144         s += ('\0' * (5 - leftover))

   145         quanta += 1

   146     for i in range(quanta):

   147         # c1 and c2 are 16 bits wide, c3 is 8 bits wide.  The intent of this

   148         # code is to process the 40 bits in units of 5 bits.  So we take the 1

   149         # leftover bit of c1 and tack it onto c2.  Then we take the 2 leftover

   150         # bits of c2 and tack them onto c3.  The shifts and masks are intended

   151         # to give us values of exactly 5 bits in width.

   152         c1, c2, c3 = struct.unpack('!HHB', s[i*5:(i+1)*5])

   153         c2 += (c1 & 1) << 16 # 17 bits wide

   154         c3 += (c2 & 3) << 8  # 10 bits wide

   155         parts.extend([_b32tab[c1 >> 11],         # bits 1 - 5

   156                       _b32tab[(c1 >> 6) & 0x1f], # bits 6 - 10

   157                       _b32tab[(c1 >> 1) & 0x1f], # bits 11 - 15

   158                       _b32tab[c2 >> 12],         # bits 16 - 20 (1 - 5)

   159                       _b32tab[(c2 >> 7) & 0x1f], # bits 21 - 25 (6 - 10)

   160                       _b32tab[(c2 >> 2) & 0x1f], # bits 26 - 30 (11 - 15)

   161                       _b32tab[c3 >> 5],          # bits 31 - 35 (1 - 5)

   162                       _b32tab[c3 & 0x1f],        # bits 36 - 40 (1 - 5)

   163                       ])

   164     encoded = EMPTYSTRING.join(parts)

   165     # Adjust for any leftover partial quanta

   166     if leftover == 1:

   167         return encoded[:-6] + '======'

   168     elif leftover == 2:

   169         return encoded[:-4] + '===='

   170     elif leftover == 3:

   171         return encoded[:-3] + '==='

   172     elif leftover == 4:

   173         return encoded[:-1] + '='

   174     return encoded

   175 

   176 

   177 def b32decode(s, casefold=False, map01=None):

   178     """Decode a Base32 encoded string.

   179 

   180     s is the string to decode.  Optional casefold is a flag specifying whether

   181     a lowercase alphabet is acceptable as input.  For security purposes, the

   182     default is False.

   183 

   184     RFC 3548 allows for optional mapping of the digit 0 (zero) to the letter O

   185     (oh), and for optional mapping of the digit 1 (one) to either the letter I

   186     (eye) or letter L (el).  The optional argument map01 when not None,

   187     specifies which letter the digit 1 should be mapped to (when map01 is not

   188     None, the digit 0 is always mapped to the letter O).  For security

   189     purposes the default is None, so that 0 and 1 are not allowed in the

   190     input.

   191 

   192     The decoded string is returned.  A TypeError is raised if s were

   193     incorrectly padded or if there are non-alphabet characters present in the

   194     string.

   195     """

   196     quanta, leftover = divmod(len(s), 8)

   197     if leftover:

   198         raise TypeError('Incorrect padding')

   199     # Handle section 2.4 zero and one mapping.  The flag map01 will be either

   200     # False, or the character to map the digit 1 (one) to.  It should be

   201     # either L (el) or I (eye).

   202     if map01:

   203         s = _translate(s, {'0': 'O', '1': map01})

   204     if casefold:

   205         s = s.upper()

   206     # Strip off pad characters from the right.  We need to count the pad

   207     # characters because this will tell us how many null bytes to remove from

   208     # the end of the decoded string.

   209     padchars = 0

   210     mo = re.search('(?P<pad>[=]*)$', s)

   211     if mo:

   212         padchars = len(mo.group('pad'))

   213         if padchars > 0:

   214             s = s[:-padchars]

   215     # Now decode the full quanta

   216     parts = []

   217     acc = 0

   218     shift = 35

   219     for c in s:

   220         val = _b32rev.get(c)

   221         if val is None:

   222             raise TypeError('Non-base32 digit found')

   223         acc += _b32rev[c] << shift

   224         shift -= 5

   225         if shift < 0:

   226             parts.append(binascii.unhexlify('%010x' % acc))

   227             acc = 0

   228             shift = 35

   229     # Process the last, partial quanta

   230     last = binascii.unhexlify('%010x' % acc)

   231     if padchars == 0:

   232         last = ''                       # No characters

   233     elif padchars == 1:

   234         last = last[:-1]

   235     elif padchars == 3:

   236         last = last[:-2]

   237     elif padchars == 4:

   238         last = last[:-3]

   239     elif padchars == 6:

   240         last = last[:-4]

   241     else:

   242         raise TypeError('Incorrect padding')

   243     parts.append(last)

   244     return EMPTYSTRING.join(parts)

   245 

   246 

   247 

   248 # RFC 3548, Base 16 Alphabet specifies uppercase, but hexlify() returns

   249 # lowercase.  The RFC also recommends against accepting input case

   250 # insensitively.

   251 def b16encode(s):

   252     """Encode a string using Base16.

   253 

   254     s is the string to encode.  The encoded string is returned.

   255     """

   256     return binascii.hexlify(s).upper()

   257 

   258 

   259 def b16decode(s, casefold=False):

   260     """Decode a Base16 encoded string.

   261 

   262     s is the string to decode.  Optional casefold is a flag specifying whether

   263     a lowercase alphabet is acceptable as input.  For security purposes, the

   264     default is False.

   265 

   266     The decoded string is returned.  A TypeError is raised if s were

   267     incorrectly padded or if there are non-alphabet characters present in the

   268     string.

   269     """

   270     if casefold:

   271         s = s.upper()

   272     if re.search('[^0-9A-F]', s):

   273         raise TypeError('Non-base16 digit found')

   274     return binascii.unhexlify(s)

   275 

   276 

   277 

   278 # Legacy interface.  This code could be cleaned up since I don't believe

   279 # binascii has any line length limitations.  It just doesn't seem worth it

   280 # though.

   281 

   282 MAXLINESIZE = 76 # Excluding the CRLF

   283 MAXBINSIZE = (MAXLINESIZE//4)*3

   284 

   285 def encode(input, output):

   286     """Encode a file."""

   287     while True:

   288         s = input.read(MAXBINSIZE)

   289         if not s:

   290             break

   291         while len(s) < MAXBINSIZE:

   292             ns = input.read(MAXBINSIZE-len(s))

   293             if not ns:

   294                 break

   295             s += ns

   296         line = binascii.b2a_base64(s)

   297         output.write(line)

   298 

   299 

   300 def decode(input, output):

   301     """Decode a file."""

   302     while True:

   303         line = input.readline()

   304         if not line:

   305             break

   306         s = binascii.a2b_base64(line)

   307         output.write(s)

   308 

   309 

   310 def encodestring(s):

   311     """Encode a string into multiple lines of base-64 data."""

   312     pieces = []

   313     for i in range(0, len(s), MAXBINSIZE):

   314         chunk = s[i : i + MAXBINSIZE]

   315         pieces.append(binascii.b2a_base64(chunk))

   316     return "".join(pieces)

   317 

   318 

   319 def decodestring(s):

   320     """Decode a string."""

   321     return binascii.a2b_base64(s)

   322 

   323 

   324 

   325 # Useable as a script...

   326 def test():

   327     """Small test program"""

   328     import sys, getopt

   329     try:

   330         opts, args = getopt.getopt(sys.argv[1:], 'deut')

   331     except getopt.error, msg:

   332         sys.stdout = sys.stderr

   333         print msg

   334         print """usage: %s [-d|-e|-u|-t] [file|-]

   335         -d, -u: decode

   336         -e: encode (default)

   337         -t: encode and decode string 'Aladdin:open sesame'"""%sys.argv[0]

   338         sys.exit(2)

   339     func = encode

   340     for o, a in opts:

   341         if o == '-e': func = encode

   342         if o == '-d': func = decode

   343         if o == '-u': func = decode

   344         if o == '-t': test1(); return

   345     if args and args[0] != '-':

   346         func(open(args[0], 'rb'), sys.stdout)

   347     else:

   348         func(sys.stdin, sys.stdout)

   349 

   350 

   351 def test1():

   352     s0 = "Aladdin:open sesame"

   353     s1 = encodestring(s0)

   354     s2 = decodestring(s1)

   355     print s0, repr(s1), s2

   356 

   357 

   358 if __name__ == '__main__':

   359     test()