Hi, Herbert, all,

akcipher can work with its own internal keys, now that we have crypto
accelerators that can generate keys that never leave the hardware. Going
through the kernel's key subsystem seems superfluous in this case.

I also understand the need of going through the kernel's key subsystem
when the user wants to refer to a key which exists elsewhere, such as in
TPM or within an SGX software enclave, but this seems orthogonal with
crypto accelerators with key generation and retention support.

How should we interface akcipher/kpp with user-space?

Thanks,
ta

On 08/17/2017 04:17 PM, Tudor Ambarus wrote:

Hi, all,

On 08/11/2017 07:05 PM, Marcel Holtmann wrote:

quoted

Hi Stephan,

quoted

quoted

AF_ALG is best suited for crypto use cases where a socket is set up 
once
and there are lots of reads and writes to justify the setup cost. With
asymmetric crypto, the setup cost is high when you might only use the
socket for a brief time to do one verify or encrypt operation.

To me, the entire AF_ALG purpose is solely to export hardware support 
to user
space. That said, if user space wants an accelerator, a socket would 
be opened
once followed by numerous read/write requests.

Besides, I am aware of Tadeusz' patch to link algif_akcipher to the 
keyring
and I planned to port it to the current implementation. But I thought 
I offer
a small patch focusing on the externalization of the akcipher API first.

I think the keyctl and AF_ALG are no opponents, but rather are 
orthogonal to
each other. The statement I made for the KPP AF_ALG RFC applies here 
too:

"""
I am aware and in fact supported development of the DH support in the 
keys
subsystem. The question will be raised whether the AF_ALG KPP 
interface is
superfluous in light of the keys DH support. My answer is that AF_ALG 
KPP is
orthogonal to the keys DH support. The keys DH support use case is that
the keys are managed inside the kernel and thus has the focus on the
key management. Contrary, AF_ALG KPP does not really focus on key 
management
but simply externalizes the DH/ECDH support found in the kernel 
including
hardware acceleration. User space is in full control of the key life 
cycle.
This way, AF_ALG could be used to complement user-space network protocol
implementations like TLS or IKE to offload the resource intense DH
calculations to accelerators.
“""

we do not need two interfaces for doing the same thing. Especially not 
one that can not handle hardware backed keys. And more important if 
you can not abstract an accelerator that doesn’t expose the private 
key at all.

I'm working with a crypto accelerator (find it at [1]) that is capable
of generating random ecc private keys internally within the device that
are never revealed outside of it. The keys can be further used for ECDH
and ECDSA.

The simplest way to access my device from user-space is to go through
af_alg. We can permit the users to provide NULL keys, and if so, we can
generate the keys inside the kernel/hardware. If hardware supports
key generation and retention, it will use it, else the keys
will be generated inside the kernel. Either way it's a win, we don't
reveal the private keys to user-space. Going through the keyring
subsystem seems superfluous in this case.

My use case compared with the one of using keyring subsystem to access
keys from TPMs or Intel's sgx enclave seem orthogonal. What do you
think?

Cheers,
ta

[1] http://www.microchip.com/wwwproducts/en/ATECC508A
The driver can be found in drivers/crypto/atmel-ecc* in Herbert's tree.