浅析sha-1和sha-256部分源码

浅析sha-1和sha-256部分源码



#define ROTL(x, n) (((x) << (n)) | ((x) >> (32 - (n))))
#define ROTR(x, n) (((x) >> (n)) | ((x) << (32 - (n))))

#define F_0_19(x, y, z) ((z) ^ ((x) & ((y) ^ (z))))
#define F_20_39(x, y, z) ((x) ^ (y) ^ (z))
#define F_40_59(x, y, z) (((x) & ((y) | (z))) | ((y) & (z)))
#define F_60_79(x, y, z) ((x) ^ (y) ^ (z))

#define DO_ROUND(F, K) { \
  temp = ROTL(a, 5) + F(b, c, d) + e + *(W++) + K; \
  e = d; \
  d = c; \
  c = ROTL(b, 30); \
  b = a; \
  a = temp; \
}

#define K_0_19 0x5a827999L
#define K_20_39 0x6ed9eba1L
#define K_40_59 0x8f1bbcdcL
#define K_60_79 0xca62c1d6L


The SHA (Secure Hash Algorithm) library.
SHA is a message digest algorithm that can be used to condense an arbitrary


void
SHA1Update (SHA1Context *sc, const void *vdata, uint32_t len)
{
  const uint8_t *data = vdata;
  uint32_t bufferBytesLeft;
  uint32_t bytesToCopy;
  int needBurn = 0;

#ifdef SHA1_FAST_COPY
  if (sc->bufferLength) {
    bufferBytesLeft = 64L - sc->bufferLength;

    bytesToCopy = bufferBytesLeft;
    if (bytesToCopy > len)
      bytesToCopy = len;

    memcpy (&sc->buffer.bytes[sc->bufferLength], data, bytesToCopy);

    sc->totalLength += bytesToCopy * 8L; // totalLength应该是bits数目

    sc->bufferLength += bytesToCopy;
    data += bytesToCopy;
    len -= bytesToCopy;

    if (sc->bufferLength == 64L) { // 蓄积了64字节raw数据,那么进行组处理
      SHA1Guts (sc, sc->buffer.words); // 以4字节word为最小单位进行digest运算,word数据依据大端模式参与
      needBurn = 1;
      sc->bufferLength = 0L;
    }
  }

  while (len > 63) {        // 多组64字节处理
    sc->totalLength += 512L; // 64*8=512bits

    SHA1Guts (sc, data);
    needBurn = 1;

    data += 64L;
    len -= 64L;
  }

  if (len) {
    memcpy (&sc->buffer.bytes[sc->bufferLength], data, len); // 非64字节整倍数

    sc->totalLength += len * 8L;

    sc->bufferLength += len;
  }
#else /* SHA1_FAST_COPY */
  while (len) {
    bufferBytesLeft = 64L - sc->bufferLength;

    bytesToCopy = bufferBytesLeft;
    if (bytesToCopy > len)
      bytesToCopy = len;

    memcpy (&sc->buffer.bytes[sc->bufferLength], data, bytesToCopy);

    sc->totalLength += bytesToCopy * 8L;

    sc->bufferLength += bytesToCopy;
    data += bytesToCopy;
    len -= bytesToCopy;

    if (sc->bufferLength == 64L) {  // 一次只处理一组64字节raw数据
      SHA1Guts (sc, sc->buffer.words);
      needBurn = 1;
      sc->bufferLength = 0L;
    }
  }
#endif /* SHA1_FAST_COPY */

  if (needBurn)
    burnStack (sizeof (uint32_t[86]) + sizeof (uint32_t *[5]) + sizeof (int));
}


static void
SHA1Guts (SHA1Context *sc, const uint32_t *cbuf)
{
  uint32_t buf[80];
  uint32_t *W, *W3, *W8, *W14, *W16;
  uint32_t a, b, c, d, e, temp;
  int i;

  W = buf;

// 从sc->buffer.words缓冲区中的16个word以大端模式拷贝到本地局部变量前16个word地址中
  for (i = 15; i >= 0; i--) {
    *(W++) = BYTESWAP(*cbuf); // 如果cpu为小端模式,那么需要将word转为大端格式数据
    cbuf++;
  }

  W16 = &buf[0];
  W14 = &buf[2];
  W8 = &buf[8];
  W3 = &buf[13];

// 相关运算,填充17-80之间这64个word空间,这样前0-15为原始数据,16-79为打散数据[luther.gliethttp]
  for (i = 63; i >= 0; i--) { // 进行全相关运算,数据打散,4字节为最小单位,64+16=80个word
    *W = *(W3++) ^ *(W8++) ^ *(W14++) ^ *(W16++);
    *W = ROTL(*W, 1);
    W++;
  }
// 至此80个word信息摘要数据源准备完毕,接下来使用这80个word数据计算出
// 一组新的a,b,c,d,e作为sc->hash[]数组的最终hash值[luther.gliethttp]

// ok,从sc->hash[]中获取a,b,c,d,e
// (hash初始值在SHA1Init()中被建立,之后每16个word数据将执行本函数SHA1Guts
//  从上一组16word计算的hash结果中接续计算新的a,b,c,d,e,这样前一组16words和
//  此次的16个words就由a,b,c,d,e关联上了,
//  于是sha就完成了对数据流进行digest摘要的工作)
  a = sc->hash[0]; // hash初始向量或上一组16word数据计算出的结果[luther.gliethttp]
  b = sc->hash[1];
  c = sc->hash[2];
  d = sc->hash[3];
  e = sc->hash[4];

  W = buf; // W指向了这80个word,下面将使用W指向的80个word计算新的a,b,c,d,e

#ifndef SHA1_UNROLL
#define SHA1_UNROLL 20 不论是SHA1_UNROLL定义为1还是20会执行DO_ROUND函数20次
// 如果为1表示20次将使用for循环执行得到,代码占用空间降低,但是效率下降
// 如果为20表示20次将使用直接顺序写入20条DO_ROUND函数实现,代码占用空间增加,但是效率提高[luther.gliethttp]
// 因为这样20*4=80个word数据才能遍历完成.
#endif /* !SHA1_UNROLL */

//printf("SHA1_UNROLL=%d\r\n", SHA1_UNROLL);
#if SHA1_UNROLL == 1  // 滚1次
  for (i = 19; i >= 0; i--)
    DO_ROUND(F_0_19, K_0_19); // 将W[0-19]与abcde参与运算,根据W[0]运算出temp,然后e=d,d=c,c=ROTL(b,30),b=a,a=temp,就像渗水一样,从a一层层的将上一层数据渗给下一层,轮换出一组新的足够打散的a,b,c,d,e

  for (i = 19; i >= 0; i--)
    DO_ROUND(F_20_39, K_20_39);

  for (i = 19; i >= 0; i--)
    DO_ROUND(F_40_59, K_40_59);

  for (i = 19; i >= 0; i--)
    DO_ROUND(F_60_79, K_60_79);
#elif SHA1_UNROLL == 2
    ......
#else /* SHA1_UNROLL */
#error SHA1_UNROLL must be 1, 2, 4, 5, 10 or 20!
#endif

  sc->hash[0] += a;
  sc->hash[1] += b;
  sc->hash[2] += c;
  sc->hash[3] += d;
  sc->hash[4] += e;
}