Added more complete RFC 3548 support for Base64, Base32, and Base16
encoding and decoding, including optional case folding and optional
alternative alphabets.
diff --git a/Lib/base64.py b/Lib/base64.py
index 3158fdc..1ef797c 100755
--- a/Lib/base64.py
+++ b/Lib/base64.py
@@ -1,36 +1,309 @@
#! /usr/bin/env python
-"""Conversions to/from base64 transport encoding as per RFC-1521."""
+"""RFC 3548: Base16, Base32, Base64 Data Encodings"""
-# Modified 04-Oct-95 by Jack to use binascii module
+# Modified 04-Oct-1995 by Jack Jansen to use binascii module
+# Modified 30-Dec-2003 by Barry Warsaw to add full RFC 3548 support
+import re
+import struct
import binascii
-__all__ = ["encode","decode","encodestring","decodestring"]
+
+__all__ = [
+ # Legacy interface exports traditional RFC 1521 Base64 encodings
+ 'encode', 'decode', 'encodestring', 'decodestring',
+ # Generalized interface for other encodings
+ 'b64encode', 'b64decode', 'b32encode', 'b32decode',
+ 'b16encode', 'b16decode',
+ # Standard Base64 encoding
+ 'standard_b64encode', 'standard_b64decode',
+ # Some common Base64 alternatives. As referenced by RFC 3458, see thread
+ # starting at:
+ #
+ # http://zgp.org/pipermail/p2p-hackers/2001-September/000316.html
+ 'freenet_b64encode', 'freenet_b64decode',
+ 'urlsafe_b64encode', 'urlsafe_b64decode',
+ ]
+
+_translation = [chr(_x) for _x in range(256)]
+EMPTYSTRING = ''
+
+
+def _translate(s, altchars):
+ translation = _translation[:]
+ for k, v in altchars.items():
+ translation[ord(k)] = v
+ return s.translate(''.join(translation))
+
+
+
+# Base64 encoding/decoding uses binascii
+
+def b64encode(s, altchars=None):
+ """Encode a string using Base64.
+
+ s is the string to encode. Optional altchars must be a string of at least
+ length 2 (additional characters are ignored) which specifies an
+ alternative alphabet for the '+' and '/' characters. This allows an
+ application to e.g. generate url or filesystem safe Base64 strings.
+
+ The encoded string is returned.
+ """
+ # Strip off the trailing newline
+ encoded = binascii.b2a_base64(s)[:-1]
+ if altchars is not None:
+ return _translate(encoded, {'+': altchars[0], '/': altchars[1]})
+ return encoded
+
+
+def b64decode(s, altchars=None):
+ """Decode a Base64 encoded string.
+
+ s is the string to decode. Optional altchars must be a string of at least
+ length 2 (additional characters are ignored) which specifies the
+ alternative alphabet used instead of the '+' and '/' characters.
+
+ The decoded string is returned. A TypeError is raised if s were
+ incorrectly padded or if there are non-alphabet characters present in the
+ string.
+ """
+ if altchars is not None:
+ s = _translate(s, {altchars[0]: '+', altchars[1]: '/'})
+ try:
+ return binascii.a2b_base64(s)
+ except binascii.Error, msg:
+ # Transform this exception for consistency
+ raise TypeError(msg)
+
+
+def standard_b64encode(s):
+ """Encode a string using the standard Base64 alphabet.
+
+ s is the string to encode. The encoded string is returned.
+ """
+ return b64encode(s)
+
+def standard_b64decode(s):
+ """Decode a string encoded with the standard Base64 alphabet.
+
+ s is the string to decode. The decoded string is returned. A TypeError
+ is raised if the string is incorrectly padded or if there are non-alphabet
+ characters present in the string.
+ """
+ return b64decode(s)
+
+def urlsafe_b64encode(s):
+ """Encode a string using a url-safe Base64 alphabet.
+
+ s is the string to encode. The encoded string is returned. The alphabet
+ uses '-' instead of '+' and '_' instead of '/'.
+ """
+ return b64encode(s, '-_')
+
+def urlsafe_b64decode(s):
+ """Decode a string encoded with the standard Base64 alphabet.
+
+ s is the string to decode. The decoded string is returned. A TypeError
+ is raised if the string is incorrectly padded or if there are non-alphabet
+ characters present in the string.
+
+ The alphabet uses '-' instead of '+' and '_' instead of '/'.
+ """
+ return b64decode(s, '-_')
+
+
+
+# Base32 encoding/decoding must be done in Python
+_b32alphabet = {
+ 0: 'A', 9: 'J', 18: 'S', 27: '3',
+ 1: 'B', 10: 'K', 19: 'T', 28: '4',
+ 2: 'C', 11: 'L', 20: 'U', 29: '5',
+ 3: 'D', 12: 'M', 21: 'V', 30: '6',
+ 4: 'E', 13: 'N', 22: 'W', 31: '7',
+ 5: 'F', 14: 'O', 23: 'X',
+ 6: 'G', 15: 'P', 24: 'Y',
+ 7: 'H', 16: 'Q', 25: 'Z',
+ 8: 'I', 17: 'R', 26: '2',
+ }
+
+_b32tab = [v for v in _b32alphabet.values()]
+_b32rev = dict([(v, long(k)) for k, v in _b32alphabet.items()])
+
+
+def b32encode(s):
+ """Encode a string using Base32.
+
+ s is the string to encode. The encoded string is returned.
+ """
+ parts = []
+ quanta, leftover = divmod(len(s), 5)
+ # Pad the last quantum with zero bits if necessary
+ if leftover:
+ s += ('\0' * (5 - leftover))
+ quanta += 1
+ for i in range(quanta):
+ # c1 and c2 are 16 bits wide, c3 is 8 bits wide. The intent of this
+ # code is to process the 40 bits in units of 5 bits. So we take the 1
+ # leftover bit of c1 and tack it onto c2. Then we take the 2 leftover
+ # bits of c2 and tack them onto c3. The shifts and masks are intended
+ # to give us values of exactly 5 bits in width.
+ c1, c2, c3 = struct.unpack('!HHB', s[i*5:(i+1)*5])
+ c2 += (c1 & 1) << 16 # 17 bits wide
+ c3 += (c2 & 3) << 8 # 10 bits wide
+ parts.extend([_b32tab[c1 >> 11], # bits 1 - 5
+ _b32tab[(c1 >> 6) & 0x1f], # bits 6 - 10
+ _b32tab[(c1 >> 1) & 0x1f], # bits 11 - 15
+ _b32tab[c2 >> 12], # bits 16 - 20 (1 - 5)
+ _b32tab[(c2 >> 7) & 0x1f], # bits 21 - 25 (6 - 10)
+ _b32tab[(c2 >> 2) & 0x1f], # bits 26 - 30 (11 - 15)
+ _b32tab[c3 >> 5], # bits 31 - 35 (1 - 5)
+ _b32tab[c3 & 0x1f], # bits 36 - 40 (1 - 5)
+ ])
+ encoded = EMPTYSTRING.join(parts)
+ # Adjust for any leftover partial quanta
+ if leftover == 1:
+ return encoded[:-6] + '======'
+ elif leftover == 2:
+ return encoded[:-4] + '===='
+ elif leftover == 3:
+ return encoded[:-3] + '==='
+ elif leftover == 4:
+ return encoded[:-1] + '='
+ return encoded
+
+
+def b32decode(s, casefold=False, map01=None):
+ """Decode a Base32 encoded string.
+
+ s is the string to decode. Optional casefold is a flag specifying whether
+ a lowercase alphabet is acceptable as input. For security purposes, the
+ default is False.
+
+ RFC 3548 allows for optional mapping of the digit 0 (zero) to the letter O
+ (oh), and for optional mapping of the digit 1 (one) to either the letter I
+ (eye) or letter L (el). The optional argument map01 when not None,
+ specifies which letter the digit 1 should be mapped to (when map01 is not
+ None, the digit 0 is always mapped to the letter O). For security
+ purposes the default is None, so that 0 and 1 are not allowed in the
+ input.
+
+ The decoded string is returned. A TypeError is raised if s were
+ incorrectly padded or if there are non-alphabet characters present in the
+ string.
+ """
+ quanta, leftover = divmod(len(s), 8)
+ if leftover:
+ raise TypeError('Incorrect padding')
+ # Handle section 2.4 zero and one mapping. The flag map01 will be either
+ # False, or the character to map the digit 1 (one) to. It should be
+ # either L (el) or I (eye).
+ if map01:
+ s = _translate(s, {'0': 'O', '1': map01})
+ if casefold:
+ s = s.upper()
+ # Strip off pad characters from the right. We need to count the pad
+ # characters because this will tell us how many null bytes to remove from
+ # the end of the decoded string.
+ padchars = 0
+ mo = re.search('(?P<pad>[=]*)$', s)
+ if mo:
+ padchars = len(mo.group('pad'))
+ if padchars > 0:
+ s = s[:-padchars]
+ # Now decode the full quanta
+ parts = []
+ acc = 0
+ shift = 35
+ for c in s:
+ val = _b32rev.get(c)
+ if val is None:
+ raise TypeError('Non-base32 digit found')
+ acc += _b32rev[c] << shift
+ shift -= 5
+ if shift < 0:
+ parts.append(binascii.unhexlify(hex(acc)[2:-1]))
+ acc = 0
+ shift = 35
+ # Process the last, partial quanta
+ last = binascii.unhexlify(hex(acc)[2:-1])
+ if padchars == 1:
+ last = last[:-1]
+ elif padchars == 3:
+ last = last[:-2]
+ elif padchars == 4:
+ last = last[:-3]
+ elif padchars == 6:
+ last = last[:-4]
+ elif padchars <> 0:
+ raise TypeError('Incorrect padding')
+ parts.append(last)
+ return EMPTYSTRING.join(parts)
+
+
+
+# RFC 3548, Base 16 Alphabet specifies uppercase, but hexlify() returns
+# lowercase. The RFC also recommends against accepting input case
+# insensitively.
+def b16encode(s):
+ """Encode a string using Base16.
+
+ s is the string to encode. The encoded string is returned.
+ """
+ return binascii.hexlify(s).upper()
+
+
+def b16decode(s, casefold=False):
+ """Decode a Base16 encoded string.
+
+ s is the string to decode. Optional casefold is a flag specifying whether
+ a lowercase alphabet is acceptable as input. For security purposes, the
+ default is False.
+
+ The decoded string is returned. A TypeError is raised if s were
+ incorrectly padded or if there are non-alphabet characters present in the
+ string.
+ """
+ if casefold:
+ s = s.upper()
+ if re.search('[^0-9A-F]', s):
+ raise TypeError('Non-base16 digit found')
+ return binascii.unhexlify(s)
+
+
+
+# Legacy interface. This code could be cleaned up since I don't believe
+# binascii has any line length limitations. It just doesn't seem worth it
+# though.
MAXLINESIZE = 76 # Excluding the CRLF
MAXBINSIZE = (MAXLINESIZE//4)*3
def encode(input, output):
"""Encode a file."""
- while 1:
+ while True:
s = input.read(MAXBINSIZE)
- if not s: break
+ if not s:
+ break
while len(s) < MAXBINSIZE:
ns = input.read(MAXBINSIZE-len(s))
- if not ns: break
- s = s + ns
+ if not ns:
+ break
+ s += ns
line = binascii.b2a_base64(s)
output.write(line)
+
def decode(input, output):
"""Decode a file."""
- while 1:
+ while True:
line = input.readline()
- if not line: break
+ if not line:
+ break
s = binascii.a2b_base64(line)
output.write(s)
+
def encodestring(s):
"""Encode a string."""
pieces = []
@@ -39,10 +312,14 @@
pieces.append(binascii.b2a_base64(chunk))
return "".join(pieces)
+
def decodestring(s):
"""Decode a string."""
return binascii.a2b_base64(s)
+
+
+# Useable as a script...
def test():
"""Small test program"""
import sys, getopt
@@ -67,11 +344,13 @@
else:
func(sys.stdin, sys.stdout)
+
def test1():
s0 = "Aladdin:open sesame"
s1 = encodestring(s0)
s2 = decodestring(s1)
print s0, `s1`, s2
+
if __name__ == '__main__':
test()