[issue29427] Option to skip padding for base64 urlsafe encoding/decoding

[uliludmann]

Change by uliludmann :


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[issue29427] Option to skip padding for base64 urlsafe encoding/decoding

[Dirkjan Ochtman]

Change by Dirkjan Ochtman :


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[issue29427] Option to skip padding for base64 urlsafe encoding/decoding

[Franklin Yu]

Change by Franklin Yu :


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[issue29427] Option to skip padding for base64 urlsafe encoding/decoding

[Mayank Asthana]

Change by Mayank Asthana :


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[issue29427] Option to skip padding for base64 urlsafe encoding/decoding

[Xiao Di Guan]

Change by Xiao Di Guan :


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[issue29427] Option to skip padding for base64 urlsafe encoding/decoding

[Guillaume]

Change by Guillaume :


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keywords: +patch
pull_requests: +6702
stage:  -> patch review

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[issue29427] Option to skip padding for base64 urlsafe encoding/decoding

[Brian Thorne]

Brian Thorne added the comment:

Hi Robert, It would be at least a week or two before I could take another look 
at this so please feel free to work on it. Not sure why I didn't write a patch 
at the time!

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[issue29427] Option to skip padding for base64 urlsafe encoding/decoding

[R. David Murray]

Changes by R. David Murray :


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[issue29427] Option to skip padding for base64 urlsafe encoding/decoding

[Robert Xiao]

Robert Xiao added the comment:

This sounds reasonable. I ran into a similar issue today trying to decode a 
JSON Web Key. Although I don't have any real say, I'd say that if you put 
together a patch it may have a higher chance to get reviewed.

I wonder about the following:

- What about adding a new kwarg to b64decode, passed through by 
urlsafe_b64decode, called "checkpad=True" which validates padding? Then we can 
just set that False when we need.
- At the same time it might be nice to pass "validate=False" through from 
urlsafe_b64decode and friends, so we can have some nicer validation of data.
- I like adding the "padding=True" arg to encode, but it may not be necessary 
given the ease of ".rstrip('=')" as an alternative. Anyway, if you will add it 
to encode, please add it to b64encode and pass through from the variant 
encoders to unify the API somewhat.

If you are still interested in putting together a patch, post a comment. 
Otherwise I may work on a patch for this.

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versions: +Python 3.6

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[issue29427] Option to skip padding for base64 urlsafe encoding/decoding

[Brian Thorne]

New submission from Brian Thorne:

Suggest changing base64 module to better handle encoding schemes that don't use 
padding. 
Because RFC4648 [1] allows other RFCs that implement RFC4648-compliant 
base64url encoding to explicitly stipulate that there is no padding. Dropping 
the padding is lossless when we know the length [2].
Various standard specifications require this - often crypto related (e.g., JWS 
[3] or named hashes [4]).

RFC4648 specifically makes an exemption for this and it should be better 
supported in Python's standard library. There is a related closed issue [5] 
asking for the padding to be removed or altered which wouldn't comply with the 
spec. This request is different with a view to better support the wider 
specification.

Proposed behaviour adapted from resolution that ruby discussion on same topic 
[6]:

- base64.urlsafe_b64encode(s) should continue to produce padded output, but 
have an additional argument, padding, which defaults to True.
- base64.urlsafe_b64decode(s) should accept both padded and unpadded inputs. It 
can still reject incorrectly-padded input.


If that sounds sensible I'd like to put a patch/PR together.

>From wikipedia [7]:

> Some variants allow or require omitting the padding '=' signs to avoid them 
> being confused with field separators, or require that any such padding be 
> percent-encoded. Some libraries will encode '=' to '.'.

- [1] https://tools.ietf.org/html/rfc4648#page-4
- [2] 
http://stackoverflow.com/questions/4080988/why-does-base64-encoding-requires-padding-if-the-input-length-is-not-divisible-b
- [3] https://tools.ietf.org/html/rfc7515
- [4] https://tools.ietf.org/html/rfc6920#section-3
- [5] http://bugs.python.org/issue1661108 
- [6] https://bugs.ruby-lang.org/issues/10740
- [7] https://en.wikipedia.org/wiki/Base64#Output_Padding

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components: Library (Lib)
messages: 286837
nosy: Thorney, georg.brandl, lemburg, loewis
priority: normal
severity: normal
status: open
title: Option to skip padding for base64 urlsafe encoding/decoding
type: behavior
versions: Python 3.7

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