Re: [dpdk-dev] [RFC] cryptodev/asymm: propose changes to modexp and modinv API

["Verma, Shally" <Shally.Verma@cavium.com>]

HI Arek

Sorry for late response. Please see response inline

From: Kusztal, ArkadiuszX <arkadiuszx.kusztal@intel.com> 
Sent: 13 December 2018 01:56
To: Verma, Shally <Shally.Verma@cavium.com>
Cc: dev@dpdk.org; Trahe, Fiona <fiona.trahe@intel.com>; Doherty, Declan <declan.doherty@intel.com>
Subject: [RFC] cryptodev/asymm: propose changes to modexp and modinv API

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Hi Shally,

I'm implementing a crypto asymmetric PMD and have some concerns about the API which I 
will work through over the next few months. Starting with modexp and modinv I have
the following questions / suggestions:

              rte_crypto_asym.h:233
                             rte_crypto_param modulus;
                             /**< modulus
                             * Prime modulus of the modexp transform operation in octet-string
                             * network byte order format.
                             */
                             [AK] - Why prime? RSA for example use semi-prime or "RSA multi-prime".
                             It should be just any positive integer.
[Shally] Hmm.. yes you're right . by the purpose of it , it is a semi-prime input.. so prime shouldn't be mentioned here.
                             [AK] - If session API layer should check if it is non-zero and set flag accordingly.
[Shally] Sorry I didn't get this.. which flag you mean here? if modulus value 0 is passed, it should be considered as INVALID_PARAM.
                             
              rte_crypto_asym.h:253
                             rte_crypto_param modulus;
                             /**<
                             * Pointer to the prime modulus data for modular
                             * inverse operation in octet-string network byte
                             * order format.
                             */
                             [AK] - Same situation as for mod exp. Just any number.
[Shally] Yea. It should be reworded as modulus data instead of *prime* modulus data

                             For example when using with RSA Carmichael and Euler Totient function will even
                             have composite factors. 
              
              rte_crypto_asym.h:323
                             struct rte_crypto_mod_op_param {
                             [AK] - There should be a result field. It size should be equal to the size
                             of modulus. Same apply to mod mult inverse. It should be driver responsability to check if result
                             will not overflow
[Shally] so these are in-place operation. Output will be written back to base param. It also imply length of allocated array should be >= modulus length which is passed in session param.

                             [AK] - Any particular reason modulus and exponent is in session? Not saying
                             it is wrong but is it for DH, RSA use cases only?
[Shally] no that's not the intent. For RSA and DH respective xforms have been defined. It is kept in session envisioning modulus and exponent wont change frequently across operation but only base value. 
So once context is loaded with modulus and exponent , app can call modexp on different base values.

                             rte_crypto.h:39
                             enum rte_crypto_op_status {
                             [AK] - There will be many more status options in asymmetric,
                             could we probably create new one for asymmetric crypto? Even if asymmetric and symmetric
                             overlap?
                             For mod exp, mod inv potentially it will be:
                            DIVIDING_BY_ZERO_ERROR, INVERSE_NOT_EXISTS_ERROR...                             
[Shally] So far RTE_CRYPTO_OP_STATUS_INVALID_PARAM has been sufficient for such cases. Do you have any use-cases where you need specific error code to indicate asym specific error codes?

              rte_crypto_asym.h:33
                             size_t length;
                             /**< length of data in bytes */
                             [AK] - Is it guaranteed to be length of actual data, not allocated memory (i mean no leading 0ed bytes), so the most significant bit will be in data[0]?
[Shally] it should be length of actual data not length of allocated memory to an array. 
However it might create bit confusion on modular exponentiation op param as that expect length passed should tell actual data length in base array but array itself should be allocated upto modulus length.

                             [AK] - could it be uint16/32_t instead as size_t can have different sizes in different implementations, uint16_t should be enough
                             for all algorithms big integer sizes 
[Shally] no hard choices here though. But size_t would never be less than uint16_t so it guarantee to be large enough for any machines
              
              rte_crypto_asym.h:74, 250, 257, 351
                             /**< Modular Inverse
                             [AK] - Modular Multiplicative Inverse
    [Shally] Ack.    

Thanks,
Arek