Added more complete RFC 3548 support for Base64, Base32, and Base16

encoding and decoding, including optional case folding and optional
alternative alphabets.

1 files changed, 288 insertions, 9 deletions

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 @@ def encodestring(s):
         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 @@ def test():
     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()