Is it safe to change the alphabet used? about shorturl HOT 3 CLOSED

Thanks, very good question!

Changing the alphabet is fine. But you have to remember four things:

• Change it once and stay with that modified alphabet forever. Obviously, if you change the alphabet again later, or if you somehow "lose" your alphabet, all IDs transformed so far will become invalid, i.e. pointing to the wrong resources.
• Shortening the alphabet makes your transformed IDs longer.
• Extending the alphabet makes your transformed IDs shorter. You don't have to worry about this if obfuscation is all you need, of course.
• Your alphabet must never contain duplicate characters.

And when using this library in general, you have to keep in mind that the ID transformation is "secure" only in the sense that it's "security through obscurity". If there is a "determined guesser", they will probably find a way to reverse the transformation. Against a layperson, however, that transformation will easily be enough as a defense.

In addition to that, an attacker will still be able to observe whether an ID is short (e.g. ms7) or long (e.g. m29slqmdf8), where the first one is a smaller number and the second one is a larger number, no matter what alphabet you're using. If you want to get rid of that property as well, and if you happen to work in PHP, you can use PHP-IDs, which is an extension of this library here.

After all, if you need to make guessing even harder, try non-sequential IDs such as UUIDs.

Does this help?

from shorturl.

This definitely helps, thanks for the detailed response! FWIW we are using mysql short UUIDs and then encoding them with this library.

We need the IDs to be easy(ish) to type using a touchscreen keyboard, so that's why we're not using just regular UUIDs. Unfortunately we've found that both the short UUID and the resulting encoded string is sequential, but I think now that we're throwing letters into the mix, the average person won't be able to guess, which is all we need.

Thanks again!

from shorturl.

the average person won't be able to guess, which is all we need

Definitely not! If that's really all you need, you should be fine.

All in all, that seems like a pretty reasonable solution for your use case. Especially in combination with MySQL's UUID_SHORT(), this will work well.

Just make sure that the implementation that you're using supports 64-bit (unsigned) integers. I don't know which (language) version you're using from this repository, but not all do support that out of the box. Some have 32-bit support only. If you're unsure, try a single large number (outside the 32-bit space), or open an issue here.

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