Use case: PKA in interrupt mode

This use case describes how to start a PKA operation and retrieve results in interrupt mode using HAL1 and HAL2.

Sequence diagram

PKA operation in interrupt mode

@startuml participant "Application" as App participant "PKA" as PKA participant "RNG" as RNG App -> RNG: HAL_RNG_Init() note right : Initialize the RNG handle and associate an instance. App -> PKA: HAL_PKA_Init() note right : Initialize the PKA handle and associate an instance. App -> PKA: HAL_PKA_ModExp_IT() @enduml

Code snippet

HAL1

HAL2 

RNG_HandleTypeDef hrng;
PKA_HandleTypeDef hpka;
PKA_ModExpInTypeDef in;
PKA_ModAddInTypeDef in2;
buffer1[0]     = 0xAA;
buffer1[26]    = 0xAA;
uint8_t *pRes  = &buffer1[1];

/* The RNG is clocked through HAL_RNG_MspInit(),
 which is called by HAL_RNG_Init() */
hrng.Instance = RNG;
HAL_RNG_Init(&hrng);

hpka.Instance = PKA;
HAL_PKA_Init(&hpka);

in.expSize = 24;
in.OpSize  = 24;
in.pOp1    = 0x55;
in.pExp    = 0x17;
in.pMod    = 0xAA;
HAL_PKA_ModExp_IT(&hpka, &in);

/* Wait for the callback function HAL_PKA_OperationCpltCallback() */
HAL_PKA_ModExp_GetResult(&hpka, pRes);

in2.size = 24;
in2.pOp1 = 0x55;
in2.pOp2 = 0x17;
in2.pOp3 = 0xAA;
HAL_PKA_ModAdd_IT(&hpka, in2);

/* Wait for the callback function HAL_PKA_OperationCpltCallback() */
HAL_PKA_Arithmetic_GetResult(&hpka, pRes);
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/* The content of the ram may be sensitive;
 if the user wants to clean it, use this function */
HAL_PKA_RAMReset(&hpka);

hal_rng_handle_t hrng;

hal_pka_handle_t hpka;
hal_pka_mod_exp_config_t config;
hal_pka_mod_add_config_t config2;
buffer1[0]         = 0xAA;
buffer1[26]        = 0xAA;
uint8_t *p_result  = &buffer1[1];

/* The PKA requires the RNG clock to be enabled */


HAL_RCC_RNG_EnableClock(void);


HAL_PKA_Init(&hpka, HAL_PKA);

config.exponent_size = 24;
config.operand_size  = 24;
config.p_operand     = 0x55;
config.p_exponent    = 0x17;
config.p_modulus     = 0xAA;
HAL_PKA_SetConfigModExp(&hpka, &config);
HAL_PKA_Compute_IT(&hpka);
/* Wait for the callback function HAL_PKA_OperationCpltCallback() */
HAL_PKA_GetResultModExp(&hpka, p_result);

config2.size_byte   = 24;
config2.p_operand_1 = 0x55;
config2.p_operand_2 = 0x17;
config2.p_operand_3 = 0xAA;
HAL_PKA_SetConfigModAdd(&hpka, &config2);
HAL_PKA_Compute_IT(&hpka);
/* Wait for the callback function HAL_PKA_OperationCpltCallback() */
HAL_PKA_GetResultAdd(&hpka, p_result);
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/* The content of the ram may be sensitive;
 if the user wants to clean it, use this function */
HAL_PKA_RAMMassErase(&hpka);

Key changes

  1. In HAL2, the operation is started in interrupt mode using HAL_PKA_Compute_IT().

  2. In HAL2, result retrieval is done using an operation-specific API after the completion callback.

  3. The sequence separates operation configuration (HAL_PKA_SetConfigModExp()) from computation start.