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
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