sha256.cpp

#include <string.h>
#include <avr/pgmspace.h>

#include "sha256.h"

const uint32_t SHA256_K[] PROGMEM = {
  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
};

const uint8_t SHA256_INIT_STATE[] PROGMEM = {
  0x67,0xe6,0x09,0x6a, // H0
  0x85,0xae,0x67,0xbb, // H1
  0x72,0xf3,0x6e,0x3c, // H2
  0x3a,0xf5,0x4f,0xa5, // H3
  0x7f,0x52,0x0e,0x51, // H4
  0x8c,0x68,0x05,0x9b, // H5
  0xab,0xd9,0x83,0x1f, // H6
  0x19,0xcd,0xe0,0x5b  // H7
};

#define ror32(num, bits) ((num << (32 - bits)) | (num >> bits))

void Sha256::init(void) {
  memcpy_P(state.b, SHA256_INIT_STATE, 32);
  byteCount = 0;
  bufferOffset = 0;
}

void Sha256::hashBlock() {
  uint8_t i;
  uint32_t a,b,c,d,e,f,g,h,t1,t2;

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

  for (i=0; i<64; i++) {
    if (i>=16) {
      t1 = buffer.w[i&15] + buffer.w[(i-7)&15];
      t2 = buffer.w[(i-2)&15];
      t1 += ror32(t2,17) ^ ror32(t2,19) ^ (t2>>10);
      t2 = buffer.w[(i-15)&15];
      t1 += ror32(t2,7) ^ ror32(t2,18) ^ (t2>>3);
      buffer.w[i&15] = t1;
    }
    t1 = h;
    t1 += ror32(e,6) ^ ror32(e,11) ^ ror32(e,25); // ∑1(e)
    t1 += g ^ (e & (g ^ f)); // Ch(e,f,g)
    t1 += pgm_read_dword(SHA256_K + i); // Ki
    t1 += buffer.w[i&15]; // Wi
    t2 = ror32(a,2) ^ ror32(a,13) ^ ror32(a,22); // ∑0(a)
    t2 += ((b & c) | (a & (b | c))); // Maj(a,b,c)
    h=g; g=f; f=e; e=d+t1; d=c; c=b; b=a; a=t1+t2;
  }
  state.w[0] += a;
  state.w[1] += b;
  state.w[2] += c;
  state.w[3] += d;
  state.w[4] += e;
  state.w[5] += f;
  state.w[6] += g;
  state.w[7] += h;
}

void Sha256::push(uint8_t data) {
  buffer.b[bufferOffset ^ 3] = data;
  bufferOffset++;
  if (bufferOffset == BLOCK_LENGTH) {
    hashBlock();
    bufferOffset = 0;
  }
}

#if defined(ARDUINO) && ARDUINO >= 100
size_t Sha256::write(uint8_t data) {
#else
void Sha256::write(uint8_t data) {
#endif
  ++byteCount;
  push(data);
#if defined(ARDUINO) && ARDUINO >= 100
  return 1;
#endif
}

void Sha256::padBlock() {
  // Implement SHA-256 padding (fips180-2 §5.1.1)

  // Pad with 0x80 followed by 0x00 until the end of the block
  push(0x80);
  while (bufferOffset != 56) push(0x00);

  // Append length in the last 8 bytes. We're only using 32 bit lengths, but
  // SHA-2 supports 64 bit lengths so zero pad the top bits
  push(0);
  push(0);
  push(0);
  push(byteCount >> 29);
  push(byteCount >> 21);
  push(byteCount >> 13);
  push(byteCount >> 5);
  push(byteCount << 3);
}

uint8_t* Sha256::result(void) {
  // Pad to complete the last block
  padBlock();

  // Swap byte order back
  for (uint8_t i = 0; i < 8; i++) {
    uint32_t a,b;
    a=state.w[i];
    b=a<<24;
    b|=(a<<8) & 0x00ff0000;
    b|=(a>>8) & 0x0000ff00;
    b|=a>>24;
    state.w[i]=b;
  }

  // Return pointer to hash
  return state.b;
}

#define HMAC_IPAD 0x36
#define HMAC_OPAD 0x5c

void Sha256::initHmac(const uint8_t *key, size_t keyLength) {
  memset(keyBuffer, 0, BLOCK_LENGTH);
  if (keyLength > BLOCK_LENGTH) {
    // Hash long keys
    init();
    for (;keyLength--;) write(*key++);
    memcpy(keyBuffer, result(), HASH_LENGTH);
  } else {
    // Block length keys are used as is
    memcpy(keyBuffer, key, keyLength);
  }
  reset();
}

uint8_t* Sha256::resultHmac(void) {
  uint8_t i;
  // Complete inner hash
  memcpy(innerHash, result(), HASH_LENGTH);
  // Calculate outer hash
  init();
  for (i = 0; i < BLOCK_LENGTH; i++) write(keyBuffer[i] ^ HMAC_OPAD);
  for (i = 0; i < HASH_LENGTH; i++) write(innerHash[i]);
  return result();
}

void Sha256::reset(void) {
  // Start inner hash
  init();
  for (uint8_t i = 0; i < BLOCK_LENGTH; i++) {
    write(keyBuffer[i] ^ HMAC_IPAD);
  }
}