Added more complete RFC 3548 support for Base64, Base32, and Base16
encoding and decoding, including optional case folding and optional alternative alphabets.
This commit is contained in:
Barry Warsaw
parent
1bc09b7c2a
commit
4c904d1bf7
297
Lib/base64.py
297
Lib/base64.py
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@ -1,36 +1,309 @@
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#! /usr/bin/env python
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"""Conversions to/from base64 transport encoding as per RFC-1521."""
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"""RFC 3548: Base16, Base32, Base64 Data Encodings"""
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# Modified 04-Oct-95 by Jack to use binascii module
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# Modified 04-Oct-1995 by Jack Jansen to use binascii module
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# Modified 30-Dec-2003 by Barry Warsaw to add full RFC 3548 support
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import re
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import struct
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import binascii
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__all__ = ["encode","decode","encodestring","decodestring"]
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__all__ = [
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# Legacy interface exports traditional RFC 1521 Base64 encodings
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'encode', 'decode', 'encodestring', 'decodestring',
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# Generalized interface for other encodings
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'b64encode', 'b64decode', 'b32encode', 'b32decode',
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'b16encode', 'b16decode',
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# Standard Base64 encoding
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'standard_b64encode', 'standard_b64decode',
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# Some common Base64 alternatives. As referenced by RFC 3458, see thread
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# starting at:
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#
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# http://zgp.org/pipermail/p2p-hackers/2001-September/000316.html
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'freenet_b64encode', 'freenet_b64decode',
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'urlsafe_b64encode', 'urlsafe_b64decode',
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]
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_translation = [chr(_x) for _x in range(256)]
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EMPTYSTRING = ''
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def _translate(s, altchars):
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translation = _translation[:]
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for k, v in altchars.items():
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translation[ord(k)] = v
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return s.translate(''.join(translation))
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# Base64 encoding/decoding uses binascii
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def b64encode(s, altchars=None):
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"""Encode a string using Base64.
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s is the string to encode. Optional altchars must be a string of at least
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length 2 (additional characters are ignored) which specifies an
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alternative alphabet for the '+' and '/' characters. This allows an
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application to e.g. generate url or filesystem safe Base64 strings.
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The encoded string is returned.
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"""
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# Strip off the trailing newline
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encoded = binascii.b2a_base64(s)[:-1]
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if altchars is not None:
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return _translate(encoded, {'+': altchars[0], '/': altchars[1]})
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return encoded
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def b64decode(s, altchars=None):
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"""Decode a Base64 encoded string.
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s is the string to decode. Optional altchars must be a string of at least
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length 2 (additional characters are ignored) which specifies the
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alternative alphabet used instead of the '+' and '/' characters.
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The decoded string is returned. A TypeError is raised if s were
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incorrectly padded or if there are non-alphabet characters present in the
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string.
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"""
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if altchars is not None:
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s = _translate(s, {altchars[0]: '+', altchars[1]: '/'})
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try:
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return binascii.a2b_base64(s)
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except binascii.Error, msg:
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# Transform this exception for consistency
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raise TypeError(msg)
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def standard_b64encode(s):
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"""Encode a string using the standard Base64 alphabet.
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s is the string to encode. The encoded string is returned.
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"""
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return b64encode(s)
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def standard_b64decode(s):
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"""Decode a string encoded with the standard Base64 alphabet.
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s is the string to decode. The decoded string is returned. A TypeError
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is raised if the string is incorrectly padded or if there are non-alphabet
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characters present in the string.
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"""
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return b64decode(s)
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def urlsafe_b64encode(s):
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"""Encode a string using a url-safe Base64 alphabet.
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s is the string to encode. The encoded string is returned. The alphabet
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uses '-' instead of '+' and '_' instead of '/'.
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"""
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return b64encode(s, '-_')
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def urlsafe_b64decode(s):
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"""Decode a string encoded with the standard Base64 alphabet.
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s is the string to decode. The decoded string is returned. A TypeError
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is raised if the string is incorrectly padded or if there are non-alphabet
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characters present in the string.
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The alphabet uses '-' instead of '+' and '_' instead of '/'.
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"""
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return b64decode(s, '-_')
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# Base32 encoding/decoding must be done in Python
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_b32alphabet = {
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0: 'A', 9: 'J', 18: 'S', 27: '3',
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1: 'B', 10: 'K', 19: 'T', 28: '4',
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2: 'C', 11: 'L', 20: 'U', 29: '5',
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3: 'D', 12: 'M', 21: 'V', 30: '6',
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4: 'E', 13: 'N', 22: 'W', 31: '7',
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5: 'F', 14: 'O', 23: 'X',
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6: 'G', 15: 'P', 24: 'Y',
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7: 'H', 16: 'Q', 25: 'Z',
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8: 'I', 17: 'R', 26: '2',
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}
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_b32tab = [v for v in _b32alphabet.values()]
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_b32rev = dict([(v, long(k)) for k, v in _b32alphabet.items()])
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def b32encode(s):
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"""Encode a string using Base32.
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s is the string to encode. The encoded string is returned.
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"""
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parts = []
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quanta, leftover = divmod(len(s), 5)
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# Pad the last quantum with zero bits if necessary
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if leftover:
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s += ('\0' * (5 - leftover))
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quanta += 1
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for i in range(quanta):
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# c1 and c2 are 16 bits wide, c3 is 8 bits wide. The intent of this
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# code is to process the 40 bits in units of 5 bits. So we take the 1
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# leftover bit of c1 and tack it onto c2. Then we take the 2 leftover
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# bits of c2 and tack them onto c3. The shifts and masks are intended
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# to give us values of exactly 5 bits in width.
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c1, c2, c3 = struct.unpack('!HHB', s[i*5:(i+1)*5])
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c2 += (c1 & 1) << 16 # 17 bits wide
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c3 += (c2 & 3) << 8 # 10 bits wide
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parts.extend([_b32tab[c1 >> 11], # bits 1 - 5
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_b32tab[(c1 >> 6) & 0x1f], # bits 6 - 10
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_b32tab[(c1 >> 1) & 0x1f], # bits 11 - 15
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_b32tab[c2 >> 12], # bits 16 - 20 (1 - 5)
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_b32tab[(c2 >> 7) & 0x1f], # bits 21 - 25 (6 - 10)
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_b32tab[(c2 >> 2) & 0x1f], # bits 26 - 30 (11 - 15)
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_b32tab[c3 >> 5], # bits 31 - 35 (1 - 5)
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_b32tab[c3 & 0x1f], # bits 36 - 40 (1 - 5)
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])
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encoded = EMPTYSTRING.join(parts)
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# Adjust for any leftover partial quanta
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if leftover == 1:
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return encoded[:-6] + '======'
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elif leftover == 2:
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return encoded[:-4] + '===='
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elif leftover == 3:
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return encoded[:-3] + '==='
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elif leftover == 4:
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return encoded[:-1] + '='
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return encoded
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def b32decode(s, casefold=False, map01=None):
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"""Decode a Base32 encoded string.
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s is the string to decode. Optional casefold is a flag specifying whether
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a lowercase alphabet is acceptable as input. For security purposes, the
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default is False.
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RFC 3548 allows for optional mapping of the digit 0 (zero) to the letter O
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(oh), and for optional mapping of the digit 1 (one) to either the letter I
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(eye) or letter L (el). The optional argument map01 when not None,
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specifies which letter the digit 1 should be mapped to (when map01 is not
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None, the digit 0 is always mapped to the letter O). For security
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purposes the default is None, so that 0 and 1 are not allowed in the
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input.
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The decoded string is returned. A TypeError is raised if s were
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incorrectly padded or if there are non-alphabet characters present in the
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string.
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"""
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quanta, leftover = divmod(len(s), 8)
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if leftover:
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raise TypeError('Incorrect padding')
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# Handle section 2.4 zero and one mapping. The flag map01 will be either
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# False, or the character to map the digit 1 (one) to. It should be
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# either L (el) or I (eye).
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if map01:
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s = _translate(s, {'0': 'O', '1': map01})
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if casefold:
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s = s.upper()
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# Strip off pad characters from the right. We need to count the pad
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# characters because this will tell us how many null bytes to remove from
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# the end of the decoded string.
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padchars = 0
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mo = re.search('(?P<pad>[=]*)$', s)
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if mo:
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padchars = len(mo.group('pad'))
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if padchars > 0:
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s = s[:-padchars]
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# Now decode the full quanta
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parts = []
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acc = 0
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shift = 35
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for c in s:
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val = _b32rev.get(c)
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if val is None:
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raise TypeError('Non-base32 digit found')
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acc += _b32rev[c] << shift
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shift -= 5
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if shift < 0:
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parts.append(binascii.unhexlify(hex(acc)[2:-1]))
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acc = 0
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shift = 35
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# Process the last, partial quanta
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last = binascii.unhexlify(hex(acc)[2:-1])
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if padchars == 1:
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last = last[:-1]
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elif padchars == 3:
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last = last[:-2]
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elif padchars == 4:
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last = last[:-3]
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elif padchars == 6:
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last = last[:-4]
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elif padchars <> 0:
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raise TypeError('Incorrect padding')
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parts.append(last)
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return EMPTYSTRING.join(parts)
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# RFC 3548, Base 16 Alphabet specifies uppercase, but hexlify() returns
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# lowercase. The RFC also recommends against accepting input case
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# insensitively.
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def b16encode(s):
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"""Encode a string using Base16.
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s is the string to encode. The encoded string is returned.
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"""
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return binascii.hexlify(s).upper()
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def b16decode(s, casefold=False):
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"""Decode a Base16 encoded string.
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s is the string to decode. Optional casefold is a flag specifying whether
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a lowercase alphabet is acceptable as input. For security purposes, the
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default is False.
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The decoded string is returned. A TypeError is raised if s were
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incorrectly padded or if there are non-alphabet characters present in the
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string.
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"""
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if casefold:
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s = s.upper()
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if re.search('[^0-9A-F]', s):
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raise TypeError('Non-base16 digit found')
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return binascii.unhexlify(s)
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# Legacy interface. This code could be cleaned up since I don't believe
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# binascii has any line length limitations. It just doesn't seem worth it
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# though.
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MAXLINESIZE = 76 # Excluding the CRLF
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MAXBINSIZE = (MAXLINESIZE//4)*3
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def encode(input, output):
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"""Encode a file."""
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while 1:
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while True:
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s = input.read(MAXBINSIZE)
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if not s: break
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if not s:
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break
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while len(s) < MAXBINSIZE:
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ns = input.read(MAXBINSIZE-len(s))
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if not ns: break
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s = s + ns
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if not ns:
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break
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s += ns
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line = binascii.b2a_base64(s)
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output.write(line)
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def decode(input, output):
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"""Decode a file."""
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while 1:
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while True:
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line = input.readline()
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if not line: break
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if not line:
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break
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s = binascii.a2b_base64(line)
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output.write(s)
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def encodestring(s):
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"""Encode a string."""
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pieces = []
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@ -39,10 +312,14 @@ def encodestring(s):
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pieces.append(binascii.b2a_base64(chunk))
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return "".join(pieces)
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def decodestring(s):
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"""Decode a string."""
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return binascii.a2b_base64(s)
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# Useable as a script...
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def test():
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"""Small test program"""
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import sys, getopt
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@ -67,11 +344,13 @@ def test():
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else:
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func(sys.stdin, sys.stdout)
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def test1():
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s0 = "Aladdin:open sesame"
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s1 = encodestring(s0)
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s2 = decodestring(s1)
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print s0, `s1`, s2
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if __name__ == '__main__':
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test()
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