text: /*********************************************************************
  * Filename:   sha256.c
  * Author:     Brad Conte (brad AT bradconte.com)
  * Copyright:
  * Disclaimer: This code is presented "as is" without any guarantees.
  * Details:    Implementation of the SHA-256 hashing algorithm.
                SHA-256 is one of the three algorithms in the SHA2
                specification. The others, SHA-384 and SHA-512, are not
                offered in this implementation.
                Algorithm specification can be found here:
                 * http://csrc.nist.gov/publications/fips/fips180-2/fips180-2withchangenotice.pdf
                This implementation uses little endian byte order.
  *********************************************************************/
  
  /*************************** HEADER FILES ***************************/
  #include <stdlib.h>
  #include <memory.h>
  
  /****************************** MACROS ******************************/
  #define ROTLEFT(a,b) (((a) << (b)) | ((a) >> (32-(b))))
  #define ROTRIGHT(a,b) (((a) >> (b)) | ((a) << (32-(b))))
  
  #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))
  #define SHA256_BLOCK_SIZE 32            /* SHA256 outputs a 32 byte digest */
  
  /**************************** DATA TYPES ****************************/
  typedef unsigned char BYTE;             /* 8-bit byte */
  typedef unsigned int  WORD;             /* 32-bit word, change to "long" for 16-bit machines */
  
  typedef struct {
  	BYTE data[64];
  	WORD datalen;
  	unsigned long long bitlen;
  	WORD state[8];
  } SHA256_CTX;
  
  /**************************** VARIABLES *****************************/
  static const WORD 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
  };
  
  /*********************** FUNCTION DEFINITIONS ***********************/
  void sha256_transform(SHA256_CTX *ctx, const BYTE data[])
  {
  	WORD 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 BYTE data[], size_t len)
  {
  	WORD i;
  
  	for (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, BYTE hash[])
  {
  	WORD i;
  
  	i = ctx->datalen;
  
  	// Pad whatever data is left in the buffer.
  	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);
  	}
  
  	/* Append to the padding the total message's length in bits and transform. */
  	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);
  
  	/* Since this implementation uses little endian byte ordering and SHA uses big endian,
  	   reverse all the bytes when copying the final state to the output hash. */
  	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 sha256sum(unsigned char *data, unsigned int length, unsigned char *hash)
  {
      SHA256_CTX ctx;
  
      sha256_init(&ctx);
      sha256_update(&ctx, data, length);
      sha256_final(&ctx, hash);
  }
  