Patch by Jeremy Katz (SF #1609407)
[python.git] / Lib / base64.py
blob41a5e1470c141dd91acae96f35c4e74390200058
1 #! /usr/bin/env python
3 """RFC 3548: Base16, Base32, Base64 Data Encodings"""
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
8 import re
9 import struct
10 import binascii
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:
24 # http://zgp.org/pipermail/p2p-hackers/2001-September/000316.html
25 'urlsafe_b64encode', 'urlsafe_b64decode',
28 _translation = [chr(_x) for _x in range(256)]
29 EMPTYSTRING = ''
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))
40 # Base64 encoding/decoding uses binascii
42 def b64encode(s, altchars=None):
43 """Encode a string using Base64.
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.
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
59 def b64decode(s, altchars=None):
60 """Decode a Base64 encoded string.
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.
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)
79 def standard_b64encode(s):
80 """Encode a string using the standard Base64 alphabet.
82 s is the string to encode. The encoded string is returned.
83 """
84 return b64encode(s)
86 def standard_b64decode(s):
87 """Decode a string encoded with the standard Base64 alphabet.
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)
95 def urlsafe_b64encode(s):
96 """Encode a string using a url-safe Base64 alphabet.
98 s is the string to encode. The encoded string is returned. The alphabet
99 uses '-' instead of '+' and '_' instead of '/'.
101 return b64encode(s, '-_')
103 def urlsafe_b64decode(s):
104 """Decode a string encoded with the standard Base64 alphabet.
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.
110 The alphabet uses '-' instead of '+' and '_' instead of '/'.
112 return b64decode(s, '-_')
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',
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()])
135 def b32encode(s):
136 """Encode a string using Base32.
138 s is the string to encode. The encoded string is returned.
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)
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
177 def b32decode(s, casefold=False, map01=None):
178 """Decode a Base32 encoded string.
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.
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.
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.
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)
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.
254 s is the string to encode. The encoded string is returned.
256 return binascii.hexlify(s).upper()
259 def b16decode(s, casefold=False):
260 """Decode a Base16 encoded string.
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.
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.
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)
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.
282 MAXLINESIZE = 76 # Excluding the CRLF
283 MAXBINSIZE = (MAXLINESIZE//4)*3
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)
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)
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)
319 def decodestring(s):
320 """Decode a string."""
321 return binascii.a2b_base64(s)
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)
351 def test1():
352 s0 = "Aladdin:open sesame"
353 s1 = encodestring(s0)
354 s2 = decodestring(s1)
355 print s0, repr(s1), s2
358 if __name__ == '__main__':
359 test()