Re: [PATCH 19/22] crypto: inside-secure - add check for xts input length equal to zero

[Horia Geantă]

On 8/10/2020 8:03 PM, Eric Biggers wrote:
> On Mon, Aug 10, 2020 at 05:33:39PM +0300, Horia Geantă wrote:
>> On 8/10/2020 4:45 PM, Herbert Xu wrote:
>>> On Mon, Aug 10, 2020 at 10:20:20AM +0000, Van Leeuwen, Pascal wrote:
>>>>
>>>> With all due respect, but this makes no sense.
>>>
>>> I agree.  This is a lot of churn for no gain.
>>>
>> I would say the gain is that all skcipher algorithms would behave the same
>> when input length equals zero - i.e. treat the request as a no-op.
>>
>> We can't say "no input" has any meaning to the other skcipher algorithms,
>> but the convention is to accept this case and just return 0.
>> I don't see why XTS has to be handled differently.
>>
> 
> CTS also rejects empty inputs.
> 
> The rule it follows is just that all input lengths >= blocksize are allowed.
> Input lengths < blocksize aren't allowed.
> 
Indeed, thanks.

What about, for example, CBC?
AFAICT cbc(aes) with input length = 0 is valid.

Same for CTR (with the note that blocksize = 1) and several other algorithms
mentioned in the cover letter.

What's the rule in these cases?

Thanks,
Horia