PSoC 6: Multiple calls to Cy_Crypto_Sha_Run

[BrVa_4472456]

I would like to use the crypto HW calculate the SHA-256 of a dataset, but can't I am unable to have all the data present in contiguous memory. Is it possible to calculate the running SHA by making subsequent calls to Cy_Crypto_Sha_Run()? Or how could this be made possible?

[DheerajK_81 · Accepted solution]

You can make use of the Core Crypto SHA PDL APIs for this purpose where there is a provision to pass chunks of data and then calculate the digest. Provided below is a simple snippet which demonstrates this.

#include "cy_pdl.h"
#include "cyhal.h"
#include "cybsp.h"
#include "cy_retarget_io.h"
#include "cy_crypto.h"
#include "cy_crypto_core.h"
#define plainTextSize 128
uint8_t sha256PlainText_1[plainTextSize] = {
     0x45, 0x11, 0x01, 0x25, 0x0e, 0xc6, 0xf2, 0x66,
     0x52, 0x24, 0x9d, 0x59, 0xdc, 0x97, 0x4b, 0x73,
     0x61, 0xd5, 0x71, 0xa8, 0x10, 0x1c, 0xdf, 0xd3,
     0x6a, 0xba, 0x3b, 0x58, 0x54, 0xd3, 0xae, 0x08,
     0x6b, 0x5f, 0xdd, 0x45, 0x97, 0x72, 0x1b, 0x66,
     0xe3, 0xc0, 0xdc, 0x5d, 0x8c, 0x60, 0x6d, 0x96,
     0x57, 0xd0, 0xe3, 0x23, 0x28, 0x3a, 0x52, 0x17,
     0xd1, 0xf5, 0x3f, 0x2f, 0x28, 0x4f, 0x57, 0xb8,
     0x5c, 0x8a, 0x61, 0xac, 0x89, 0x24, 0x71, 0x1f,
     0x89, 0x5c, 0x5e, 0xd9, 0x0e, 0xf1, 0x77, 0x45,
     0xed, 0x2d, 0x72, 0x8a, 0xbd, 0x22, 0xa5, 0xf7,
     0xa1, 0x34, 0x79, 0xa4, 0x62, 0xd7, 0x1b, 0x56,
     0xc1, 0x9a, 0x74, 0xa4, 0x0b, 0x65, 0x5c, 0x58,
     0xed, 0xfe, 0x0a, 0x18, 0x8a, 0xd2, 0xcf, 0x46,
     0xcb, 0xf3, 0x05, 0x24, 0xf6, 0x5d, 0x42, 0x3c,
     0x83, 0x7d, 0xd1, 0xff, 0x2b, 0xf4, 0x62, 0xac
};
/* Calculated SHA-256 digest */
uint8_t sha256Digest[CY_CRYPTO_SHA256_DIGEST_SIZE] = {0};
uint8_t shaBuffer[plainTextSize] = {0};
int main(void)
{
     cy_rslt_t result;
     /* Initialize the device and board peripherals */
     result = cybsp_init();
     /* Board init failed. Stop program execution */
     if (result != CY_RSLT_SUCCESS)
     {
          CY_ASSERT(0);
     }
     /* Enable global interrupts */
     __enable_irq();
     /* Initialize retarget-io to use the debug UART port */
     result = cy_retarget_io_init(CYBSP_DEBUG_UART_TX, CYBSP_DEBUG_UART_RX, \
     CY_RETARGET_IO_BAUDRATE);
     /* retarget-io init failed. Stop program execution */
     if (result != CY_RSLT_SUCCESS)
     {
          CY_ASSERT(0);
     }
     /* \x1b[2J\x1b[;H - ANSI ESC sequence for clear screen */
     printf("\x1b[2J\x1b[;H");
     printf("****************** "
     "PSoC 6 SHA Calculation Example "
     "****************** \r\n\n");
     uint8_t* messagePtr = (uint8_t*)sha256PlainText_1;
     uint32_t messageSize = sizeof(sha256PlainText_1);
     /* Enable the Crypto block */
     Cy_Crypto_Core_Enable(CRYPTO);
     cy_en_crypto_status_t tmpResult = CY_CRYPTO_BAD_PARAMS;
     /* Allocate space for the structure which stores the SHA context */
     cy_stc_crypto_sha_state_t hashState = { 0 };
     tmpResult = Cy_Crypto_Core_Sha_Init(CRYPTO, &hashState, CY_CRYPTO_MODE_SHA256, (uint8_t*)shaBuffer);
     /* Start the Hash of the message by SHA256 */
     if (CY_CRYPTO_SUCCESS == tmpResult)
     {
          printf("Start calculation \n\r");
          tmpResult = Cy_Crypto_Core_Sha_Start(CRYPTO, &hashState);
     }
     /* Process all chunks of the message */
     while ((messageSize != 0) && (CY_CRYPTO_SUCCESS == tmpResult))
     {
          uint32_t chunkSize = (messageSize >= CY_CRYPTO_SHA256_BLOCK_SIZE) ? CY_CRYPTO_SHA256_BLOCK_SIZE : messageSize;
          tmpResult = Cy_Crypto_Core_Sha_Update (CRYPTO, &hashState, messagePtr, chunkSize);
          messagePtr += chunkSize;
          messageSize -= chunkSize;
     }
     if (CY_CRYPTO_SUCCESS == tmpResult)
     {
          tmpResult = Cy_Crypto_Core_Sha_Finish(CRYPTO, &hashState, sha256Digest);
     }
     if (CY_CRYPTO_SUCCESS == tmpResult)
     {
          tmpResult = Cy_Crypto_Core_Sha_Free(CRYPTO, &hashState);
     }
     printf("Calculated digest: \n\r");
     for(int i = 0; i < CY_CRYPTO_SHA256_DIGEST_SIZE; i++){
          if((i > 0) && (i % 8 == 0)){
               printf("\n\r");
          }
          printf("0x%0X  ", sha256Digest & 0xFF);
     }
printf("\r\nDemonstration complete \n\r");
}

Hope this helps!

Regards,

Dheeraj

[BrVa_4472456]

Yes! Thank you the above template worked for me. Just curious though, I was having problems until I made the hash, SHA buffer, and message buffer global variables. I was figuring having them as locals was fine since I was calling the crypto functions all within the function scope, any insight?

[JeHu_3414236]

If you are using Cy_Crypto_Sha_Run() the documentation says the message and digest address must be 4-byte aligned.  Maybe declaring the buffer as global instead of local just happens to place them at 4-byte aligned addresses.

[DheerajK_81]

I declared them in the local scope and was able to observe the output. Not sure what's going wrong in your case, please attach your main.c file so that I can have a look.

And yes, JeHu_3414236​ suggestion to align it on a 4-byte boundary can be done to see if it works. You can do it this way:

CY_ALIGN(4) uint8_t sha256Digest[CY_CRYPTO_SHA256_DIGEST_SIZE] = {0};

Regards,

Dheeraj