1:mod:`base64` --- Base16, Base32, Base64, Base85 Data Encodings 2=============================================================== 3 4.. module:: base64 5 :synopsis: RFC 4648: Base16, Base32, Base64 Data Encodings; 6 Base85 and Ascii85 7 8**Source code:** :source:`Lib/base64.py` 9 10.. index:: 11 pair: base64; encoding 12 single: MIME; base64 encoding 13 14-------------- 15 16This module provides functions for encoding binary data to printable 17ASCII characters and decoding such encodings back to binary data. 18It provides encoding and decoding functions for the encodings specified in 19:rfc:`4648`, which defines the Base16, Base32, and Base64 algorithms, 20and for the de-facto standard Ascii85 and Base85 encodings. 21 22The :rfc:`4648` encodings are suitable for encoding binary data so that it can be 23safely sent by email, used as parts of URLs, or included as part of an HTTP 24POST request. The encoding algorithm is not the same as the 25:program:`uuencode` program. 26 27There are two interfaces provided by this module. The modern interface 28supports encoding :term:`bytes-like objects <bytes-like object>` to ASCII 29:class:`bytes`, and decoding :term:`bytes-like objects <bytes-like object>` or 30strings containing ASCII to :class:`bytes`. Both base-64 alphabets 31defined in :rfc:`4648` (normal, and URL- and filesystem-safe) are supported. 32 33The legacy interface does not support decoding from strings, but it does 34provide functions for encoding and decoding to and from :term:`file objects 35<file object>`. It only supports the Base64 standard alphabet, and it adds 36newlines every 76 characters as per :rfc:`2045`. Note that if you are looking 37for :rfc:`2045` support you probably want to be looking at the :mod:`email` 38package instead. 39 40 41.. versionchanged:: 3.3 42 ASCII-only Unicode strings are now accepted by the decoding functions of 43 the modern interface. 44 45.. versionchanged:: 3.4 46 Any :term:`bytes-like objects <bytes-like object>` are now accepted by all 47 encoding and decoding functions in this module. Ascii85/Base85 support added. 48 49The modern interface provides: 50 51.. function:: b64encode(s, altchars=None) 52 53 Encode the :term:`bytes-like object` *s* using Base64 and return the encoded 54 :class:`bytes`. 55 56 Optional *altchars* must be a :term:`bytes-like object` of at least 57 length 2 (additional characters are ignored) which specifies an alternative 58 alphabet for the ``+`` and ``/`` characters. This allows an application to e.g. 59 generate URL or filesystem safe Base64 strings. The default is ``None``, for 60 which the standard Base64 alphabet is used. 61 62 63.. function:: b64decode(s, altchars=None, validate=False) 64 65 Decode the Base64 encoded :term:`bytes-like object` or ASCII string 66 *s* and return the decoded :class:`bytes`. 67 68 Optional *altchars* must be a :term:`bytes-like object` or ASCII string of 69 at least length 2 (additional characters are ignored) which specifies the 70 alternative alphabet used instead of the ``+`` and ``/`` characters. 71 72 A :exc:`binascii.Error` exception is raised 73 if *s* is incorrectly padded. 74 75 If *validate* is ``False`` (the default), characters that are neither 76 in the normal base-64 alphabet nor the alternative alphabet are 77 discarded prior to the padding check. If *validate* is ``True``, 78 these non-alphabet characters in the input result in a 79 :exc:`binascii.Error`. 80 81 82.. function:: standard_b64encode(s) 83 84 Encode :term:`bytes-like object` *s* using the standard Base64 alphabet 85 and return the encoded :class:`bytes`. 86 87 88.. function:: standard_b64decode(s) 89 90 Decode :term:`bytes-like object` or ASCII string *s* using the standard 91 Base64 alphabet and return the decoded :class:`bytes`. 92 93 94.. function:: urlsafe_b64encode(s) 95 96 Encode :term:`bytes-like object` *s* using the 97 URL- and filesystem-safe alphabet, which 98 substitutes ``-`` instead of ``+`` and ``_`` instead of ``/`` in the 99 standard Base64 alphabet, and return the encoded :class:`bytes`. The result 100 can still contain ``=``. 101 102 103.. function:: urlsafe_b64decode(s) 104 105 Decode :term:`bytes-like object` or ASCII string *s* 106 using the URL- and filesystem-safe 107 alphabet, which substitutes ``-`` instead of ``+`` and ``_`` instead of 108 ``/`` in the standard Base64 alphabet, and return the decoded 109 :class:`bytes`. 110 111 112.. function:: b32encode(s) 113 114 Encode the :term:`bytes-like object` *s* using Base32 and return the 115 encoded :class:`bytes`. 116 117 118.. function:: b32decode(s, casefold=False, map01=None) 119 120 Decode the Base32 encoded :term:`bytes-like object` or ASCII string *s* and 121 return the decoded :class:`bytes`. 122 123 Optional *casefold* is a flag specifying 124 whether a lowercase alphabet is acceptable as input. For security purposes, 125 the default is ``False``. 126 127 :rfc:`4648` allows for optional mapping of the digit 0 (zero) to the letter O 128 (oh), and for optional mapping of the digit 1 (one) to either the letter I (eye) 129 or letter L (el). The optional argument *map01* when not ``None``, specifies 130 which letter the digit 1 should be mapped to (when *map01* is not ``None``, the 131 digit 0 is always mapped to the letter O). For security purposes the default is 132 ``None``, so that 0 and 1 are not allowed in the input. 133 134 A :exc:`binascii.Error` is raised if *s* is 135 incorrectly padded or if there are non-alphabet characters present in the 136 input. 137 138 139.. function:: b32hexencode(s) 140 141 Similar to :func:`b32encode` but uses the Extended Hex Alphabet, as defined in 142 :rfc:`4648`. 143 144 .. versionadded:: 3.10 145 146 147.. function:: b32hexdecode(s, casefold=False) 148 149 Similar to :func:`b32decode` but uses the Extended Hex Alphabet, as defined in 150 :rfc:`4648`. 151 152 This version does not allow the digit 0 (zero) to the letter O (oh) and digit 153 1 (one) to either the letter I (eye) or letter L (el) mappings, all these 154 characters are included in the Extended Hex Alphabet and are not 155 interchangeable. 156 157 .. versionadded:: 3.10 158 159 160.. function:: b16encode(s) 161 162 Encode the :term:`bytes-like object` *s* using Base16 and return the 163 encoded :class:`bytes`. 164 165 166.. function:: b16decode(s, casefold=False) 167 168 Decode the Base16 encoded :term:`bytes-like object` or ASCII string *s* and 169 return the decoded :class:`bytes`. 170 171 Optional *casefold* is a flag specifying whether a 172 lowercase alphabet is acceptable as input. For security purposes, the default 173 is ``False``. 174 175 A :exc:`binascii.Error` is raised if *s* is 176 incorrectly padded or if there are non-alphabet characters present in the 177 input. 178 179 180.. function:: a85encode(b, *, foldspaces=False, wrapcol=0, pad=False, adobe=False) 181 182 Encode the :term:`bytes-like object` *b* using Ascii85 and return the 183 encoded :class:`bytes`. 184 185 *foldspaces* is an optional flag that uses the special short sequence 'y' 186 instead of 4 consecutive spaces (ASCII 0x20) as supported by 'btoa'. This 187 feature is not supported by the "standard" Ascii85 encoding. 188 189 *wrapcol* controls whether the output should have newline (``b'\n'``) 190 characters added to it. If this is non-zero, each output line will be 191 at most this many characters long. 192 193 *pad* controls whether the input is padded to a multiple of 4 194 before encoding. Note that the ``btoa`` implementation always pads. 195 196 *adobe* controls whether the encoded byte sequence is framed with ``<~`` 197 and ``~>``, which is used by the Adobe implementation. 198 199 .. versionadded:: 3.4 200 201 202.. function:: a85decode(b, *, foldspaces=False, adobe=False, ignorechars=b' \\t\\n\\r\\v') 203 204 Decode the Ascii85 encoded :term:`bytes-like object` or ASCII string *b* and 205 return the decoded :class:`bytes`. 206 207 *foldspaces* is a flag that specifies whether the 'y' short sequence 208 should be accepted as shorthand for 4 consecutive spaces (ASCII 0x20). 209 This feature is not supported by the "standard" Ascii85 encoding. 210 211 *adobe* controls whether the input sequence is in Adobe Ascii85 format 212 (i.e. is framed with <~ and ~>). 213 214 *ignorechars* should be a :term:`bytes-like object` or ASCII string 215 containing characters to ignore 216 from the input. This should only contain whitespace characters, and by 217 default contains all whitespace characters in ASCII. 218 219 .. versionadded:: 3.4 220 221 222.. function:: b85encode(b, pad=False) 223 224 Encode the :term:`bytes-like object` *b* using base85 (as used in e.g. 225 git-style binary diffs) and return the encoded :class:`bytes`. 226 227 If *pad* is true, the input is padded with ``b'\0'`` so its length is a 228 multiple of 4 bytes before encoding. 229 230 .. versionadded:: 3.4 231 232 233.. function:: b85decode(b) 234 235 Decode the base85-encoded :term:`bytes-like object` or ASCII string *b* and 236 return the decoded :class:`bytes`. Padding is implicitly removed, if 237 necessary. 238 239 .. versionadded:: 3.4 240 241 242The legacy interface: 243 244.. function:: decode(input, output) 245 246 Decode the contents of the binary *input* file and write the resulting binary 247 data to the *output* file. *input* and *output* must be :term:`file objects 248 <file object>`. *input* will be read until ``input.readline()`` returns an 249 empty bytes object. 250 251 252.. function:: decodebytes(s) 253 254 Decode the :term:`bytes-like object` *s*, which must contain one or more 255 lines of base64 encoded data, and return the decoded :class:`bytes`. 256 257 .. versionadded:: 3.1 258 259 260.. function:: encode(input, output) 261 262 Encode the contents of the binary *input* file and write the resulting base64 263 encoded data to the *output* file. *input* and *output* must be :term:`file 264 objects <file object>`. *input* will be read until ``input.read()`` returns 265 an empty bytes object. :func:`encode` inserts a newline character (``b'\n'``) 266 after every 76 bytes of the output, as well as ensuring that the output 267 always ends with a newline, as per :rfc:`2045` (MIME). 268 269 270.. function:: encodebytes(s) 271 272 Encode the :term:`bytes-like object` *s*, which can contain arbitrary binary 273 data, and return :class:`bytes` containing the base64-encoded data, with newlines 274 (``b'\n'``) inserted after every 76 bytes of output, and ensuring that 275 there is a trailing newline, as per :rfc:`2045` (MIME). 276 277 .. versionadded:: 3.1 278 279 280An example usage of the module: 281 282 >>> import base64 283 >>> encoded = base64.b64encode(b'data to be encoded') 284 >>> encoded 285 b'ZGF0YSB0byBiZSBlbmNvZGVk' 286 >>> data = base64.b64decode(encoded) 287 >>> data 288 b'data to be encoded' 289 290.. _base64-security: 291 292Security Considerations 293----------------------- 294 295A new security considerations section was added to :rfc:`4648` (section 12); it's 296recommended to review the security section for any code deployed to production. 297 298.. seealso:: 299 300 Module :mod:`binascii` 301 Support module containing ASCII-to-binary and binary-to-ASCII conversions. 302 303 :rfc:`1521` - MIME (Multipurpose Internet Mail Extensions) Part One: Mechanisms for Specifying and Describing the Format of Internet Message Bodies 304 Section 5.2, "Base64 Content-Transfer-Encoding," provides the definition of the 305 base64 encoding. 306 307