Re: [Question] AEAD crypto api for userspace can't deal with a PTlen=0 vector

[Yao Dongdong <yaodongdong@huawei.com>]

On 2015/5/7 19:28, Stephan Mueller wrote:
> Am Donnerstag, 7. Mai 2015, 17:44:53 schrieb Yao Dongdong:
>
> Hi Yao,
>
>> while we use crypto api for userspace to do vectors test for AEAD(aes-gcm),
>> we encounter a problem. There are some test vector's PTlen is 0,for example:
>> [Keylen = 128]
>> [IVlen = 96]
>> [PTlen = 0]
>> [AADlen = 0]
>> [Taglen = 128]
>>
>> Count = 0
>> Key = 7e93936b2e2188cfa9c9882ad901312f
>> IV = b6879804163b9eaf5bfe5218
>> CT =
>> AAD =
>> Tag = aa77daf382d0d63480ff8c8a2dee149e
>>
>> In testing vectors like that, we will get an error result that the decrypt
>> return is success but the right return is a ghash verify fail.
>> After digging into the kernel(3.10) code, we find the function sock_aio_read
>> in net/socket.c has a judgement of iocb->ki_left which will be 0 when we
>> do an aes-gcm decrypt decribed above.
>>
>> static ssize_t sock_aio_read(struct kiocb *iocb, const struct iovec *iov,
>>                unsigned long nr_segs, loff_t pos)
>> {
>>    struct sock_iocb siocb, *x;
>>
>>    if (pos != 0)
>>        return -ESPIPE;
>>
>>    if (iocb->ki_left == 0) /* Match SYS5 behaviour */
>>        return 0;
>>
>>    x = alloc_sock_iocb(iocb, &siocb);
>>    if (!x)
>>        return -ENOMEM;
>>    return do_sock_read(&x->async_msg, iocb, iocb->ki_filp, iov, nr_segs);
>> }
>>
>> So it directly return before calling aes-gcm decrypt.
>>
>> How can we deal with that?
> You cannot. Currently, the interface is not intended to handle such specific 
> CAVS conditions (zero CT and AAD). Note, this test effectively only validates 
> GHASH.
>
> In any case, if you need to perform CAVS testing, you will only be able to do 
> that with a kernel module for all obscure operations CAVS requests (not only 
> for AEAD, but also for RNGs).
>
> Or you restrict your usage (and thus the CAVS testing) to CT/AAD lengths > 0.

Thanks for your replay and we will modify our treatment based on your suggestions.

>
> Ciao
> Stephan
>
> .
>


-- 
Kind regards,
Yao Dongdong