Hi All,
I am developping a driver for a crypto offloading solution which
uses the AF_ALG interface. I am trying to stay as close as possible to
the specification but apart from the kernel crypto source code and a few
documents (such as
https://www.kernel.org/doc/htmldocs/crypto-API/ch04s06.html ) I have not
found a lot of details on AF_ALG specification and many points are not
very clear to me, it someone could point me towards reference to answer
the following questions it will be deeply appreciated.
*
**
Socket / Connection :
Is it legal to open multiple connections on an AF_ALG socket ? How is
the behavior defined
*From what I could test, at least for digests, multiple connections are
OK, but it seems odd to allow multiple connection to a cipher while
using a**shared key and multiple IVs. One of the use I could think of
will be parallelizing several encryption/decryption with the same
symmetric key.
*
Is it true that the key (defined via setsockopt) is common to all the
connections but the IV (defined through message control header) is
specific to each connection ?
*
*
Send/Recv interleaving
When computing a digest (e.g. sha256) it seems the recv call is
triggering the end of the digest accumulation, such a behavior can be
obtained by using/not using MSG_MORE flags, which *of the two*the
canonical way to compute a hash over several send messages ? It does not
seem possible to compute a partial digest (through a recv call) and then
continue accumulating through other send calls (apart from the security
risk of exposing a te*mporary digest, is there a reason why the recv
ends a digest computation ?)*.*
*
AES-GCM / AEAD
Does the aead_assoclen must be set once and for all for each stream or
is it a by message option ?
Option 0: set aead_assoclen during the first sendmsg and then stream
accross several sendmsg the full AAD and then the full plaintext/ciphertext
Option 1: set aead_assoclen for each of the first sendmsg containing aad
data. Once the aead_assoclen is strictly less than the msg’s data length
then the next messages must have aead_assoclen set to 0
*
best regards,
Nicolas Brunie
Am Dienstag, 26. Juli 2016, 13:48:21 CEST schrieb Nicolas Brunie:
Hi Nicolas,
> Hi All,
> I am developping a driver for a crypto offloading solution which
> uses the AF_ALG interface. I am trying to stay as close as possible to
> the specification but apart from the kernel crypto source code and a few
> documents (such as
> https://www.kernel.org/doc/htmldocs/crypto-API/ch04s06.html ) I have not
> found a lot of details on AF_ALG specification and many points are not
> very clear to me, it someone could point me towards reference to answer
> the following questions it will be deeply appreciated.
See [1] for the library around it.
> *
> **
>
> Socket / Connection :
>
> Is it legal to open multiple connections on an AF_ALG socket ? How is
> the behavior defined
Yes, you get a handle (i.e. a file descriptor) for each connection.
>
> *From what I could test, at least for digests, multiple connections are
> OK, but it seems odd to allow multiple connection to a cipher while
> using a**shared key and multiple IVs. One of the use I could think of
> will be parallelizing several encryption/decryption with the same
> symmetric key.
It is allowed
> *
>
> Is it true that the key (defined via setsockopt) is common to all the
> connections but the IV (defined through message control header) is
> specific to each connection ?
Yes.
>
> *
> *
>
> Send/Recv interleaving
>
> When computing a digest (e.g. sha256) it seems the recv call is
> triggering the end of the digest accumulation, such a behavior can be
> obtained by using/not using MSG_MORE flags, which *of the two*the
> canonical way to compute a hash over several send messages ? It does not
> seem possible to compute a partial digest (through a recv call) and then
> continue accumulating through other send calls (apart from the security
> risk of exposing a te*mporary digest, is there a reason why the recv
> ends a digest computation ?)*.*
You can read intermediary results. recv does not check for the MSG_MORE flag.
>
> *
>
> AES-GCM / AEAD
>
> Does the aead_assoclen must be set once and for all for each stream or
> is it a by message option ?
Assoclen is handled like the IV, per message where a message may be sent in
multiple chunks.
>
> Option 0: set aead_assoclen during the first sendmsg and then stream
> accross several sendmsg the full AAD and then the full plaintext/ciphertext
>
> Option 1: set aead_assoclen for each of the first sendmsg containing aad
> data. Once the aead_assoclen is strictly less than the msg’s data length
> then the next messages must have aead_assoclen set to 0
Option 1, if I read your text right.
>
> *
[1] http://www.chronox.de/libkcapi.html
>
> best regards,
> Nicolas Brunie
> --
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Ciao
Stephan
Hi,
On 07/26/2016 04:54 AM, Stephan Mueller wrote:
>> > Is it true that the key (defined via setsockopt) is common to all the
>> > connections but the IV (defined through message control header) is
>> > specific to each connection ?
> Yes.
I think that's not correct. Please define a "connection".
If you think of connections as separate sockets, then you can
have different keys for each socket. The difference is that
you set a key per each socket once, and you send IV for each
operation (encrypt/decrypt).
Thanks,
--
TS
Hi,
In my understanding, a socket is the file descriptor given as argument to a bind call and a connection is the file descriptor returned by an accept call.
NB
----- Mail original -----
De: "Tadeusz Struk" <[email protected]>
À: "Stephan Mueller" <[email protected]>, "Nicolas Brunie" <[email protected]>
Cc: "Linux Crypto Mailing List" <[email protected]>
Envoyé: Mardi 26 Juillet 2016 16:37:51
Objet: Re: a few questions on AF_ALG specification (AEAD, socket/connection, ...)
Hi,
On 07/26/2016 04:54 AM, Stephan Mueller wrote:
>> > Is it true that the key (defined via setsockopt) is common to all the
>> > connections but the IV (defined through message control header) is
>> > specific to each connection ?
> Yes.
I think that's not correct. Please define a "connection".
If you think of connections as separate sockets, then you can
have different keys for each socket. The difference is that
you set a key per each socket once, and you send IV for each
operation (encrypt/decrypt).
Thanks,
--
TS
Am Montag, 1. August 2016, 11:14:07 CEST schrieb Nicolas Brunie:
Hi Nicolas,
> Hi,
> In my understanding, a socket is the file descriptor given as argument to
> a bind call and a connection is the file descriptor returned by an accept
> call.
This would be an appropriate naming:
The key is set on a socket. The IV is given with the connection.
>
> NB
>
>
>
> ----- Mail original -----
> De: "Tadeusz Struk" <[email protected]>
> ?: "Stephan Mueller" <[email protected]>, "Nicolas Brunie"
> <[email protected]> Cc: "Linux Crypto Mailing List"
> <[email protected]>
> Envoy?: Mardi 26 Juillet 2016 16:37:51
> Objet: Re: a few questions on AF_ALG specification (AEAD, socket/
connection,
> ...)
>
> Hi,
>
> On 07/26/2016 04:54 AM, Stephan Mueller wrote:
> >> > Is it true that the key (defined via setsockopt) is common to all the
> >> > connections but the IV (defined through message control header) is
> >> > specific to each connection ?
> >
> > Yes.
>
> I think that's not correct. Please define a "connection".
> If you think of connections as separate sockets, then you can
> have different keys for each socket. The difference is that
> you set a key per each socket once, and you send IV for each
> operation (encrypt/decrypt).
> Thanks,
Ciao
Stephan