possible characters base64 url safe function

Question

What is the range of possible characters returned from this string?

function base64url_encode($data) 
{ 
  return rtrim(strtr(base64_encode($data), '+/', '-_'), '='); 
}

My guess is [a-z0-9-_]

base64 is case sensitive. so that should be a-zA-Z0-9-_ – Jonathan Kuhn May 23 '11 at 19:43 — Jonathan Kuhn, May 23 '11 at 19:43

score 48 · Answer 1 · edited Dec 26 '20 at 14:52

48

Base64 encoded strings may contain the characters a-z A-Z 0-9 + / =.

You're removing the right-padding = and replacing + with - and / with _.

So in your case, the possible characters are a-z A-Z 0-9 - _

edited Dec 26 '20 at 14:52

huysentruitw

answered May 23 '11 at 19:53

Floern

salathe · Accepted Answer · 2014-05-21T08:17:54.637

45

The range of possible characters returned are:

In your regex-style, that would be [a-zA-Z0-9_-].

edited May 21 '14 at 08:17

answered May 23 '11 at 19:52

salathe

13

sorry to revive an old post.. but it's worth mentioning that `base64encode` likes to add `=` to the end of some string as "padding" to keep string length a modulo 4 number. See answer: http://stackoverflow.com/a/4492448/648350 – haxxxton Aug 20 '14 at 06:50
5

@haxxxton and those `=` are being explicitly `rtrim`-ed in the question's `base64url_encode` function. – salathe Aug 20 '14 at 15:49
5

@salathe agreed, i just thought it was worth mentioning what the default behaviour for `base64encode` was, as when i was searching for what it's possible values were, this was one of the first posts that came up :) – haxxxton Aug 20 '14 at 23:55
8

there is also an '=' equal sign just like this string "RElMR19OZXdzX0NlbnRyYWxfMjAxMTExMThfZGE2NTU0NjI0Zi5qcGc=.jpg" – Frederick G. Sandalo Jan 05 '15 at 10:10
2

@FrederickG.Sandalo check the original question, the equals sign (=) is getting (r)trimmed. – salathe Jan 05 '15 at 13:44
1

ahhh yeah, I didnt notice the rtrim() function there – Frederick G. Sandalo Jan 05 '15 at 17:11

2 Answers2