Re: Asymmetric cryptography HW offloading

["Horia Geantă" <horia.geanta@freescale.com>]

On 9/23/2013 4:28 PM, Nikos Mavrogiannopoulos wrote:
> On 09/23/2013 02:31 PM, Horia Geantă wrote:
>> Hi,
>>
>> CAAM crypto engine (drivers/crypto/caam/*) is capable of asymmetric
>> operations, like: modular exponentiation, RSA
>> sign/verify/encrypt/decrypt, (EC)DSA sign etc.
>> I would appreciate some design guidelines on how to harness these
>> capabilities, for crypto engines in general.
>>
>> 1. In-kernel interface for asymmetric crypto
>> Should crypto/asymmetric_keys/* be used, i.e. appended with modular
>> exponentiation, other asymmetric operations?
> The BSD's cryptodev supports the following operations which may help in
> that aspect (no elliptic curve operations present). I don't know if all
> of them worth the context switch.
>
> #define CRK_MOD_EXP		0
> #define CRK_MOD_EXP_CRT		1
> #define CRK_DSA_SIGN		2
> #define CRK_DSA_VERIFY		3
> #define CRK_DH_COMPUTE_KEY	4
> #define CRK_MOD_ADD		5
> #define CRK_MOD_ADDINV		6
> #define CRK_MOD_SUB		7
> #define CRK_MOD_MULT		8
> #define CRK_MOD_MULTINV		9
> #define CRK_MOD			10

Thanks for the tip.
I took a look at BSD - AFAICT there is no SW implementation and crypto 
engine drivers handle only the first two operations (MOD_EXP).

My main concern now is the asymmetric ciphers API, that would eventually 
allow implementing the operations in SW/HW.
I was wondering whether the same logic as for symmetric ciphers 
could/should be used (the API layering mentioned in 
Documentation/crypto/api-intro.txt).
For example, crypto/asymmetric_keys/rsa.c could be registered and then 
used via Crypto API:
rsa.c: crypto_alg->cra_name = "rsa"; 
crypto_alg->cra_driver_name="rsa-generic"; crypto_register_alg(crypto_alg);
user: tfm = crypto_alloc_tfm("rsa",...);
User would get either the "rsa-generic" SW implementation or a HW 
implementation, if available.

>
>> 2. User space interface
>> Should AF_ALG be expanded to provide access to this new asymmetric cypto
>> API? The API would allow user space applications to offload PKC operations in
>> HW.
> I'd be interested into adding this support into cryptodev-linux once
> present in kernel.

Thanks.
We already have a draft implementation of asymmetric crypto + 
cryptodev-linux, but was developed prior to crypto/asymmetric_keys 
addition and thus has to be reworked.

Horia