SHA256.ino

// https://github.com/rweather/arduinolibs/tree/master/libraries/Crypto
#include <SHA256.h>

#define HASH_SIZE 32 // Bytes
#define LED_PIN   2  // LED pin to blink while we crunch SHA256
#define debug     0

// SHA256 via C++ char strings (much faster than Arduino Strings)
char *sha256hex(const char *input, char *outhex) {
	SHA256 hash;
	uint8_t output[HASH_SIZE]; // Raw byte array of the sha256 output

	strcpy(outhex,"");

	hash.reset();
	hash.update(input, strlen(input));
	hash.finalize(output, HASH_SIZE);

	for (int i = 0; i < HASH_SIZE; i++) {
		uint8_t c = output[i];

		sprintf(eos(outhex), "%02x", c);
	}

	return outhex;
}

// Return a string (*much* slower than C strings)
String sha256hex(const String input) {
	char tmp[65];
	sha256hex(input.c_str(),tmp);

	String output_hex = tmp;

	return output_hex;
}

char *random_string(char *ret) {
	char words[][6] = {
		"apple", "world", "smart", "phone", "toons", "yearn", "write", "vixen", "unite", "tutor", "swing", "roman",
		"rosey", "quote", "psych", "overy", "novel", "muggy", "lumpy", "knots", "joker", "ingot", "hunch", "guide",
		"furry", "elves", "dizzy", "cubed", "bumby", "atone", "magic", "smell", "speak", "glass", "board", "elbow",
	};

	int total = sizeof(words) / sizeof(words[0]);
	strcpy(ret,"");

	// Word #1
	strcat(ret,words[random(0,total)]);

	// Random numbers in the middle
	char num[3];
	itoa(random(0,99),num,10);
	strcat(ret,num);

	// Word #2
	strcat(ret,words[random(0,total)]);

	return ret;
}

char *eos(char str[]) {
	return (str) + strlen(str);
}

///////////////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////

long int start = 0;
int count      = 0;
char buf[100];

void setup() {
	Serial.begin(115200);
	delay(500);

	Serial.print("Starting hash tests\r\n");

	start = millis();
	pinMode(LED_PIN, OUTPUT);
	digitalWrite(LED_PIN, LOW);
}

void loop() {
	char input[15] = "";
	random_string(input);

	digitalWrite(LED_PIN, HIGH);
	char output_hex[65] = "";
	sha256hex(input,output_hex);
	digitalWrite(LED_PIN, LOW);

	if (debug) {
		sprintf(buf, "SHA256: %-12s = %s\r\n", input, output_hex);
		Serial.print(buf);
	}

	count++;

	// Output some stats every 10 seconds
	if ((millis() - start) > 10000) {
		sprintf(buf, "Crunched %d SHA256 sums in 10 seconds\r\n",count);
		Serial.print(buf);

		// Reset the variables for a new loop
		count = 0;
		start = millis();
	}
}