// ESP32 SHA-256 (C Algoritm)
// https://emn178.github.io/online-tools/sha256.html

// Hello, World!
// dffd6021bb2bd5b0af676290809ec3a53191dd81c7f70a4b28688a362182986f

// https://wokwi.com/projects/407045345171632129 - ESP32 HMAC SHA-256
// https://wokwi.com/projects/407044309018040321 - ESP32 SHA-256 Accelerator Test (MicroPython)

//#include <stdio.h>    // for gcc
//#include <stdint.h>   // for gcc
//#include <string.h>   // for gcc

typedef struct {
  uint8_t data[64];
  uint32_t datalen;
  unsigned long long bitlen;
  uint32_t state[8];
} SHA256_CTX;

#define ROTRIGHT(word, bits) (((word) >> (bits)) | ((word) << (32 - (bits))))

#define CH(x, y, z) (((x) & (y)) ^ (~(x) & (z)))
#define MAJ(x, y, z) (((x) & (y)) ^ ((x) & (z)) ^ ((y) & (z)))

#define EP0(x) (ROTRIGHT(x, 2) ^ ROTRIGHT(x, 13) ^ ROTRIGHT(x, 22))
#define EP1(x) (ROTRIGHT(x, 6) ^ ROTRIGHT(x, 11) ^ ROTRIGHT(x, 25))
#define SIG0(x) (ROTRIGHT(x, 7) ^ ROTRIGHT(x, 18) ^ ((x) >> 3))
#define SIG1(x) (ROTRIGHT(x, 17) ^ ROTRIGHT(x, 19) ^ ((x) >> 10))

const uint32_t k[64] = {
  0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
  0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
  0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
  0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
  0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
  0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
  0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
  0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2
};

void sha256_transform(SHA256_CTX* ctx, const uint8_t data[]) {
  uint32_t a, b, c, d, e, f, g, h, i, j, t1, t2, m[64];

  for (i=0, j=0; i<16; ++i, j += 4) {
    m[i] = (data[j] << 24) | (data[j + 1] << 16) | (data[j + 2] << 8) | (data[j + 3]);
  }

  for (; i<64; ++i) {
    m[i] = SIG1(m[i - 2]) + m[i - 7] + SIG0(m[i - 15]) + m[i - 16];
  }

  a = ctx->state[0];
  b = ctx->state[1];
  c = ctx->state[2];
  d = ctx->state[3];
  e = ctx->state[4];
  f = ctx->state[5];
  g = ctx->state[6];
  h = ctx->state[7];

  for (i=0; i<64; ++i) {
    t1 = h + EP1(e) + CH(e, f, g) + k[i] + m[i];
    t2 = EP0(a) + MAJ(a, b, c);
    h = g;
    g = f;
    f = e;
    e = d + t1;
    d = c;
    c = b;
    b = a;
    a = t1 + t2;
  }

  ctx->state[0] += a;
  ctx->state[1] += b;
  ctx->state[2] += c;
  ctx->state[3] += d;
  ctx->state[4] += e;
  ctx->state[5] += f;
  ctx->state[6] += g;
  ctx->state[7] += h;
}

void sha256_init(SHA256_CTX* ctx) {
  ctx->datalen = 0;
  ctx->bitlen = 0;
  ctx->state[0] = 0x6a09e667;
  ctx->state[1] = 0xbb67ae85;
  ctx->state[2] = 0x3c6ef372;
  ctx->state[3] = 0xa54ff53a;
  ctx->state[4] = 0x510e527f;
  ctx->state[5] = 0x9b05688c;
  ctx->state[6] = 0x1f83d9ab;
  ctx->state[7] = 0x5be0cd19;
}

void sha256_update(SHA256_CTX* ctx, const uint8_t data[], size_t len) {
  for (size_t i=0; i<len; ++i) {
    ctx->data[ctx->datalen] = data[i];
    ctx->datalen++;
    if (ctx->datalen == 64) {
      sha256_transform(ctx, ctx->data);
      ctx->bitlen += 512;
      ctx->datalen = 0;
    }
  }
}

void sha256_final(SHA256_CTX* ctx, uint8_t hash[]) {
  uint32_t i = ctx->datalen;

  if (ctx->datalen < 56) {
    ctx->data[i++] = 0x80;
    while (i<56) {ctx->data[i++] = 0x00;}
  } else {
    ctx->data[i++] = 0x80;
    while (i<64) {ctx->data[i++] = 0x00;}
    sha256_transform(ctx, ctx->data);
    memset(ctx->data, 0, 56);
  }

  ctx->bitlen += ctx->datalen * 8;
  ctx->data[63] = ctx->bitlen;
  ctx->data[62] = ctx->bitlen >> 8;
  ctx->data[61] = ctx->bitlen >> 16;
  ctx->data[60] = ctx->bitlen >> 24;
  ctx->data[59] = ctx->bitlen >> 32;
  ctx->data[58] = ctx->bitlen >> 40;
  ctx->data[57] = ctx->bitlen >> 48;
  ctx->data[56] = ctx->bitlen >> 56;

  sha256_transform(ctx, ctx->data);

  for (i=0; i<4; ++i) {
    hash[i] = (ctx->state[0] >> (24 - i * 8)) & 0x000000ff;
    hash[i + 4] = (ctx->state[1] >> (24 - i * 8)) & 0x000000ff;
    hash[i + 8] = (ctx->state[2] >> (24 - i * 8)) & 0x000000ff;
    hash[i + 12] = (ctx->state[3] >> (24 - i * 8)) & 0x000000ff;
    hash[i + 16] = (ctx->state[4] >> (24 - i * 8)) & 0x000000ff;
    hash[i + 20] = (ctx->state[5] >> (24 - i * 8)) & 0x000000ff;
    hash[i + 24] = (ctx->state[6] >> (24 - i * 8)) & 0x000000ff;
    hash[i + 28] = (ctx->state[7] >> (24 - i * 8)) & 0x000000ff;
  }
}

void sha256(const char* input, const uint16_t len, uint8_t* outputHash) {
  SHA256_CTX ctx;
  sha256_init(&ctx);
  sha256_update(&ctx, (const unsigned char*)input, len);
  sha256_final(&ctx, outputHash);
}

// For gcc
//size_t calculateStringLength(const char* str) {
//  size_t length = 0;
//  while (str[length] != '\0') {length++;}
//  return length;
//}

void setup() {
  Serial.begin(115200);
  Serial.println();
  char* input = "Hello, World!";
  Serial.println(input);
  uint16_t len = strlen(input);	  // len = 13 // calculateStringLength(input);  // for gcc
  uint8_t hash[32];
  uint64_t time = micros();
  sha256(input, len, hash);
  time = micros()-time;
  for (uint16_t i=0; i<32; ++i) {
    char str[3];
		sprintf(str, "%02x", (uint16_t)hash[i]);
		Serial.print(str);  // printf("%02x", hash[i]); // for gcc
  }
  Serial.printf("\nTime: %llu us", time);		// Time: 633 us

	Serial.println("\n");
	Serial.println(input);
  uint8_t hash2[32];
  time = micros();
  sha256(input, len, hash2);
  time = micros()-time;
  for (uint16_t i=0; i<32; ++i) {
    char str[3];
		sprintf(str, "%02x", (uint16_t)hash2[i]);
		Serial.print(str);  // printf("%02x", hash[i]); // for gcc
  }
  Serial.printf("\nTime: %llu us", time);		// Time: 632 us
}

void loop() {}