Expose raw blockcipher primitive (was: Missing padding-options for AES-encryption)

[benbender]

I need to encrypt data to interact with an API-implementation outside of my control. The api expects data to be encrypted via AES/CBC/NoPadding. I can't seem to find an option to set padding for SymmetricEncryptionAlgorithm.AES.

I'm not quite sure if this option is missing or if I am missing something?

[JesusMcCloud]

SymmetricEncryptionAlgorithm.AES_128.CBC.PLAIN ;-). Or whichever keysize you prefer. You can also wire up all parameters yourself, if desired

My bad! No padding is unsupported out of the box. if you really need this, you will currently have to construct this yourself using ECB (and since you use no padding, this is just an XOR chain).

There will be overhead, but it's currently the only way.

@iaik-jheher in case you are keeping score: you just got a point for "expose the block cipher primitive"

[benbender]

Thanks for digging into it! I really need this option as my API is a javacard-applet which has very limited cipher-support.

Since I'm not entirely sure how to approach this, are there any examples, tests, or similar that describe the procedure to construct the cipher?

PS: Thanks for your work on this great library. Very appreciated! <3

[JesusMcCloud]

I was too quick again. Seems like we need to expose the raw block cipher primitive, because ECB also adds passing.

Since the low-level operations are already there, we should be able to make it happen without too much delay.

With the raw blockcipher primitive exposed, the sky is the limit…

[benbender]

Just to be sure: In the meantime there is no option to construct a NoPadding-Cipher within signum, correct?

[JesusMcCloud]

Sorry to say, but no :( We'll track progress here but at the moment I cannot give an ETA. Feel free to open a PR. Building locally should work out of the box. If you want to experiment:

• supreme/androidJvmMain has AES/ECB Alg identifier strings in there with padding, copy the pattern, adapt to nopadding to expose a raw block primitive
• supreme/iosMain does the padding manually anyways, so to expose the block cipher primtive, the existing code without the padding logic can be re-used and just wired into a "expose raw block cipher" function

[JesusMcCloud]

@benbender feel free to take #411 for a spin

[benbender]

Thx for putting in the effort. Will do as soon as I find a minute! <3

[JesusMcCloud]

Just to be clear: this is really just a band-aid and not a clean exposure of the raw block cipher primitive. it should fit your use-case though.

[benbender]

Yes, already had a look. Especially because its kind of a bandaid-solution for my use-case: Thank you very much for your effort! <3