base64.py

#! /usr/bin/env python

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

# 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__ = [
    # 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
    '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('%010x' % acc))
            acc = 0
            shift = 35
    # Process the last, partial quanta
    last = binascii.unhexlify('%010x' % acc)
    if padchars == 0:
        last = ''                       # No characters
    elif padchars == 1:
        last = last[:-1]
    elif padchars == 3:
        last = last[:-2]
    elif padchars == 4:
        last = last[:-3]
    elif padchars == 6:
        last = last[:-4]
    else:
        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 True:
        s = input.read(MAXBINSIZE)
        if not s:
            break
        while len(s) < MAXBINSIZE:
            ns = input.read(MAXBINSIZE-len(s))
            if not ns:
                break
            s += ns
        line = binascii.b2a_base64(s)
        output.write(line)


def decode(input, output):
    """Decode a file."""
    while True:
        line = input.readline()
        if not line:
            break
        s = binascii.a2b_base64(line)
        output.write(s)


def encodestring(s):
    """Encode a string."""
    pieces = []
    for i in range(0, len(s), MAXBINSIZE):
        chunk = s[i : i + MAXBINSIZE]
        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
    try:
        opts, args = getopt.getopt(sys.argv[1:], 'deut')
    except getopt.error, msg:
        sys.stdout = sys.stderr
        print msg
        print """usage: %s [-d|-e|-u|-t] [file|-]
        -d, -u: decode
        -e: encode (default)
        -t: encode and decode string 'Aladdin:open sesame'"""%sys.argv[0]
        sys.exit(2)
    func = encode
    for o, a in opts:
        if o == '-e': func = encode
        if o == '-d': func = decode
        if o == '-u': func = decode
        if o == '-t': test1(); return
    if args and args[0] != '-':
        func(open(args[0], 'rb'), sys.stdout)
    else:
        func(sys.stdin, sys.stdout)


def test1():
    s0 = "Aladdin:open sesame"
    s1 = encodestring(s0)
    s2 = decodestring(s1)
    print s0, repr(s1), s2


if __name__ == '__main__':
    test()