Using SHA-256 with an ESP32

In this example we will look at how you can generate the hash of a string using the SHA-256 algorithm. We will use the Arduino IDE in which the ESP32 core by luck has a builtin mbed TLS libraries.

If you want to ready more about SHA-2 then start at https://en.wikipedia.org/wiki/SHA-2 and read through this, its a nice introduction

Code

#include "mbedtls/md.h"

void setup()
{
Serial.begin(115200);

char *payload = "Hello SHA 256 from ESP32learning";
byte shaResult[32];

mbedtls_md_context_t ctx;
mbedtls_md_type_t md_type = MBEDTLS_MD_SHA256;

const size_t payloadLength = strlen(payload);

mbedtls_md_init(&ctx);
mbedtls_md_setup(&ctx, mbedtls_md_info_from_type(md_type), 0);
mbedtls_md_starts(&ctx);
mbedtls_md_update(&ctx, (const unsigned char *) payload, payloadLength);
mbedtls_md_finish(&ctx, shaResult);
mbedtls_md_free(&ctx);

Serial.print("Hash: ");

for(int i= 0; i< sizeof(shaResult); i++)
{
char str[3];
sprintf(str, "%02x", (int)shaResult[i]);
Serial.print(str);
}
}

void loop()
{
}

Testing

Open the serial monitor window , press the reset button on your board and you should see something like this

rst:0x1 (POWERON_RESET),boot:0x13 (SPI_FAST_FLASH_BOOT)
ets Jun 8 2016 00:22:57

rst:0x10 (RTCWDT_RTC_RESET),boot:0x13 (SPI_FAST_FLASH_BOOT)
configsip: 0, SPIWP:0x00
clk_drv:0x00,q_drv:0x00,d_drv:0x00,cs0_drv:0x00,hd_drv:0x00,wp_drv:0x00
mode:DIO, clock div:1
load:0x3fff0008,len:8
load:0x3fff0010,len:160
load:0x40078000,len:10632
load:0x40080000,len:252
entry 0x40080034
Hash: 2fd33178d3f9a3da6bf046d097cada788bbbb74e5fa2c430dc0e8d24bf3fa6ac

The key thing is the hash, you then need to locate a sha256 hash generator tool on the internet and double check the hash above is correct. i will use the one at https://passwordsgenerator.net/sha256-hash-generator/ mainly because I could screen capture the text and the output

You can see my results here