Remove all code that supports AES-192

[briansmith]

See

ring/crypto/aes/aes.c

Lines 549 to 551 in c882c2c

	case 192:
	aeskey->rounds = 12;
	break;

and

ring/crypto/aes/aes.c

Lines 549 to 551 in c882c2c

	case 192:
	aeskey->rounds = 12;
	break;

Also, I guess the assembly language code must have some bits that support 192-bit AES.

We don't need any of this since we don't (and don't plan to) expose AES-192.

[briansmith]

Done in fc99d30.

[lawliet89]

@briansmith May I know the reasons behind not supporting AES-192? Just curious to know because I am working on a library to implement JSON Web Encryption in Rust and AES-192 is one of the algorithms in the standard.

[briansmith]

@lawliet89

Basically, it was removed:

1. Because of lack of tests and review.
2. Because nobody is using it in the real world.
3. To discourage people from implementing it in higher-level things, because of (1) and (2)

Note that Chrome's WebCrypto API implementation also skips AES-192; see https://diafygi.github.io/webcrypto-examples/.

Regarding JOSE, I recommend that you don't try to implement everything in the spec. Checkboxes are pretty but it's better to have solid implementations of fewer primitives than to check all the boxes.

[lawliet89]

Thanks for your detailed reply.