Passing base64 encoded strings in URL

Question

Is it safe to pass raw base64 encoded strings via GET parameters?

Answer 1

No, you would need to url-encode it, since base64 strings can contain the "+", "=" and "/" characters which could alter the meaning of your data - look like a sub-folder.

Valid base64 characters are below.

ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=

Answer 2

There are additional base64 specs. (See the table here for specifics ). But essentially you need 65 chars to encode: 26 lowercase + 26 uppercase + 10 digits = 62.

You need two more ['+', '/'] and a padding char '='. But none of them are url friendly, so just use different chars for them and you're set. The standard ones from the chart above are ['-', '_'], but you could use other chars as long as you decoded them the same, and didn't need to share with others.

I'd recommend just writing your own helpers. Like these from the comments on the php manual page for base64_encode:

function base64_url_encode($input) {
 return strtr(base64_encode($input), '+/=', '._-');
}

function base64_url_decode($input) {
 return base64_decode(strtr($input, '._-', '+/='));
}

Answer 3

@joeshmo Or instead of writing a helper function, you could just urlencode the base64 encoded string. This would do the exact same thing as your helper function, but without the need of two extra functions.

$str = 'Some String';

$encoded = urlencode( base64_encode( $str ) );
$decoded = base64_decode( urldecode( $encoded ) );

Answer 4

Introductory Note I'm inclined to post a few clarifications since some of the answers here were a little misleading (if not incorrect).

The answer is NO, you cannot simply pass a base64 encoded parameter within a URL query string since plus signs are converted to a SPACE inside the $_GET global array. In other words, if you sent test.php?myVar=stringwith+sign to

//test.php
print $_GET['myVar'];

the result would be:
stringwith sign

The easy way to solve this is to simply urlencode() your base64 string before adding it to the query string to escape the +, =, and / characters to %## codes. For instance, urlencode("stringwith+sign") returns stringwith%2Bsign

When you process the action, PHP takes care of decoding the query string automatically when it populates the $_GET global. For example, if I sent test.php?myVar=stringwith%2Bsign to

//test.php
print $_GET['myVar'];

the result would is:
stringwith+sign

You do not want to urldecode() the returned $_GET string as +'s will be converted to spaces.
In other words if I sent the same test.php?myVar=stringwith%2Bsign to

//test.php
$string = urldecode($_GET['myVar']);
print $string;

the result is an unexpected:
stringwith sign

It would be safe to rawurldecode() the input, however, it would be redundant and therefore unnecessary.

Answer 5

Yes and no.

The basic charset of base64 may in some cases collide with traditional conventions used in URLs. But many of base64 implementations allow you to change the charset to match URLs better or even come with one (like Python's urlsafe_b64encode()).

Another issue you may be facing is the limit of URL length or rather — lack of such limit. Because standards do not specify any maximum length, browsers, servers, libraries and other software working with HTTP protocol may define its' own limits.

Answer 6

Its a base64url encode you can try out, its just extension of joeshmo's code above.

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

function base64url_decode($data) {
return base64_decode(str_pad(strtr($data, '-_', '+/'), strlen($data) % 4, '=', STR_PAD_RIGHT));
}

Answer 7

I don't think that this is safe because e.g. the "=" character is used in raw base 64 and is also used in differentiating the parameters from the values in an HTTP GET.

Answer 8

In theory, yes, as long as you don't exceed the maximum url and/oor query string length for the client or server.

In practice, things can get a bit trickier. For example, it can trigger an HttpRequestValidationException on ASP.NET if the value happens to contain an "on" and you leave in the trailing "==".

Answer 9

For url safe encode, like base64.urlsafe_b64encode(...) in Python the code below, works to me for 100%

function base64UrlSafeEncode(string $input)
{
   return str_replace(['+', '/'], ['-', '_'], base64_encode($input));
}